text:
Talk:Green Party/Pre-2013 redirect archive

Merge?
Ralph Nader is purposely not linked to from here, because he's not in (any) Green Party and he's not a representative green party politician. -- I am considering, as per the previous request to compare the two articles, removing most of this as it is 100% redundant with the new "Green Parties" entry.
 * Attribution unclear because of later alterations (Anthony Appleyard (talk) 12:03, 2 December 2012 (UTC)).

the term "green Party" and the term "green party" have variant uses that are not necessarily under control of the Green Parties, and which the Green Parties in general try to deny.

I'd define a small-g "green party" (informal, colloquial), or a big-p "green Party" ( formally organized party sharing some 'green' objectives) as being one that isn't one of the Green Parties necessarily, and maybe doesn't share all the Four Pillars or all the Ten Key Values.

as in, "socialist party" or "conservative party" which are generic terms.

That has the advantage that it leaves "Green Parties" more or less presenting Green Parties as they understand and present themselves, with only a few notes of criticism and controversy, but it gives "green party" controversy unrelated to the specific big-G program a place to live... like a more historical less political perspective.

If there are objections to that approach, let me know, before I implement it.

thanks

Someone is not reading the talk before making major changes.

The redirect needs to be undone. The article here is about generic small-g green party definition - and points to the larger and well known movement of Green Parties.

Which now (wrongly) redirects itself here.

This *REALLY PROVES* the need to have small-g "green" and big-G "Green" as different entries. dammit.

This is getting more wrong all the time. Green Parties do not define what is a Green Party. Members of Green Parties do not define what is a Green Party. The Four Pillars do not define what is a Green Party.

"writing for the enemy", remember? A "green party" (small g) is a party that is built on environmental goals. Whether or not it also accepts the peace movement goals. If I want to discredit the Green Parties, I point to the Libertarian National Socialist Green Party, or the Marijuana Parties, and I exploit the confusion, and I fuzz the issue of the Four Pillars. So, the use of "green party" generically is real, and important, and still quite useful.

However, the Green Parties, Green Movement, and Greens (who could be either), all use that big-G Green in its proper sense.

The correct approach here is to restore the article under the title Green Parties (there is no "shorthand name" for any "group of parties" - this is wrong - there is a proposal by Green Parties to create a new international Green Party, and a GlobalGreens Charter that *some* of them agree to - two separate initiatives), and restore the article under "green party" which made the differentiation between a generally small-g "green party" compared to "socialist party" or "conservative party", and the specific Green Parties committed to the Four Pillars/ Ten Key Values.

I am *enraged* at this point at the spurious capitalization of entries, i.e. "green" versus "Green", which is literally destroying the integrity of them all.

--- There is no such thing as "'small-g' Green Parties" - spurious capitalization is making this article a mess.

There is, however, such a thing as a "'small-g green party" - including the values party, ecology party, etc., that predate the modern Green Parties, and the marijuana parties, and even the LNSGP.

"Green_party" and "Green_Party" need to be restored to the generic entry that outlines the generic use, and points to the separate entry on "Green_Parties".

The second article which has been jammed into the text here is already complete, and already contains all the text of the original article, with the exception of some incorrect introduction material, such as "shorthand name"...
 * 16:30, 25 March 2002 User:24.150.61.63

24: you can't have distinct 'Green party' and 'green party' entries in the Wikipedia using the current software. You are apparently "*enraged*" by other people's attempts to clean up your mess. I'm amused that you are now issuing instructions to other authors. Hint: try playing well with others, first. The Anome
 * 17:01, 25 March 2002 User:The Anome

No, it's the stupid user interface that adds spurious capitals that is the only thing enraging me. I know what a good user interface is, and one that confuses generic and Proper names is not one...

I didn't *ask* for distinct "Green party" and "green party" entries anyway, it was "green Party" that needs to be distinguished from "Green Party" in this case. The two entries are required for the use of "libertarian" vs. "Libertarian" - the equivalent for "green" is pointless as that term is too abused to use other than politically - unlike "Green" which is much more specific and almost always means "adhering to the Four Pillars"

Anyway, all that is required now is to restore the "green Party" entry I had written just prior to this one, and put the "second article" presently visible back at "Green_Parties" which properly and plurally describes the several big-G Green Parties - and *only* them.

I don't see any instructions here for undoing a diff under "editing help" so I assume it's a special function easier for some people to do than others?

 * Hit "History", then view your old version, edit it, then save it (I think). Then we can add this to editing help.

Or, are you all just diffing and copying when you restore? If so I'll just do it myself.

point of order: *I* didn't create the mess, whoever shoved the two articles into one did that... I'm just asking not to have the corrections stomped on...
 * 17:12, 25 March 2002 User:24.150.61.63

Hi, I think we have to watch the vibes here. Assuming your co-editors are acting in good faith helps us all a lot. It's really easy to misunderstand ASCII, so please be extra careful to try not to offend. Those were my weasel words "shorthand name" (written before the meeting in Australia, IIRC) and I'm not particularly proud of them but it would help make my world a more beautiful place if I didn't wander into random accusations. Peace, DanKeshet
 * 17:26, 25 March 2002 User:DanKeshet

It is actually a bug that current Wiki software allows case-sensitivity in titles at all, and that is not a feature we ever intended to make use of. Such liguistic conventions are not really the focus of an encyclopedia, and will confuse readers more than enlighten them. If not using them confuses writers, well, tough. It's readers that count. Writers are presumed intelligent enough to deal with such things. And please, please, don't elevate such stylistic nuances to the level of "correctness"--such hubris certainly has no place here. If you think a change in the software would make something better for users, then discuss it with the community in the appropriate places, and we agree with might do it. But we might not; in that case, work within the software you've got. --LDC --- The convention as it stands is provably wrong. Open any dictionary or any encyclopedia. None of them assume an equivalence of Proper and generic names. Any English style guide can tell you the difference and why there is one.
 * 17:33, 25 March 2002 User:Lee Daniel Crocker

Now, there's an argument that we should rely on them minimally, since other languages like Deutsch or francais use different conventions.

Software isn't the problem in this case. It's actually part of language.

As to "shorthand name", the original article was fine as far as it went, and that's why I kept all of it. It just assumed some things like the equivalence of a proto "green Party" and Four-Pillars-type "Green Parties", the universal acceptance of the GG Charter, the equivalence of 'ecology' and 'environment' (two different things), and not distinguishing ethics from platforms.

Anyway...

The crazy-making part here is that someone jams two articles together, asks for them to be reconciled when they already are, stomps on the entry that made the careful distinction, then someone else accuses *me* of making a mess...

I'll let this sit for a while so that anyone who wants to undo the mess they created can do so. If not, I'll fix it later when the people who are making the accusations aren't around, and I can be sure it won't get stomped on... tonight. ;-)
 * 17:41, 25 March 2002 User:24.150.61.63

If there's a useful (and generally recognized) distinction to be made between two related subjects, you're probably more qualified than I to make it, so please do so. But let's find something other than mere letter case to distinguish them and put them into articles with appropriate titles, with a disambiguating page pointing to them. We do our readers no service by blindly adopting such a confusing convention without explaining it in the process. Titles should be clear and easy to understand--like "Green party (generic term)" and "Green Party (organization)". Article titles begin with uppercase; no exceptions. --LDC - That still doesn't work as "Green party" and "green party" are both generic. Sorry, the user interface convention is wrong, period, and is going to lead eventually to things like "(small-g) green party" and "(big-G) Green party" (which I've heard used as a distinction) and more reasonable stuff like "(the Four-Pillar) Green Parties". If that's what you want, that's where we go... and this is exactly where trademark law already is - 'Coke' is not 'coke' etc.
 * 18:00, 25 March 2002 User:Lee Daniel Crocker

The article I had here (in "green Party") made the distinction in the first sentence and described clearly the relationship to "Green Parties" as such. The link at "green party" now does the same (although i didn't write that).

Subtle cognitive distinction here:

Asking the question "What is a Green Party?" implies a definition i.e. of a conceivable new Green Party, whereas asking "What are the Green Parties?" implies a history of some specific entities that already exist. That's very standard usage.

The "green" versus "Green" is a matter of claims, i.e. how does one *test* for "green"-ness or "Green"-ness, and there are answers to that. One could even write an article on "green versus Green" if so inclined.

But, in this user interface, that comes out "Green versus green" and doesn't make sense as it could have been "green versus green" before the GUI hacked it.

Messy. - alright, this is done now, and "green party" redirects to "green Party" since big-P implies a formally registered political party in some jurisdiction... which I'm not satisfied the LNSGP is, but, well... who wants to annoy nazis?
 * 19:57, 25 March 2002 User:24.150.61.63

It might be messy and difficult, but it's a good writer's job to make it clear. I'm a writer--I'm very good at it, and I know how to make things clear to people and how to work within the limitations of different media. I'm going to retitle these articles--after I do, please make a genuine effort to consider that I might know what I'm doing and that it might serve your purpose to leave them titled the way I do it, or at least try to reach a community consensus before changing it. --LDC
 * 20:01, 25 March 2002 User:Lee Daniel Crocker

why don't you try to reach a community consensus *BEFORE* changing it? We just went through this, don't make us do so again.

The distinction is confusing BECAUSE THE USAGE IS CONFUSING - the job of the articles is to clear that up. If they don't, they need to be rewritten USING THE TERMS AS THEY ARE EXTANT. I have only been lectured about this ten times now...

That said, if you make it absolutely clear that "Green" means something more specific than "green", and that there are Parties that are Green but no real point inventing a fictional association of Parties that are merely green... fine. I think the titles as they stand do that fine. To be "Parties" you need two that acknowledge each other as moral equivalents... to be a Party you dont... people who don't understand that just don't understand "party".
 * 20:05, 25 March 2002 User:24.150.61.63

Why can't you just create a "green party" entry and then explain in the entry that the term capitalized has a special meaning? The two meanings are close enough together that a single article should be sufficient. Most people searching for "green party" won't know that they really should have searched for "Green Party". AxelBoldt --- That's exactly what I did. "green party" and "green Party" end up at the same entry. It makes a point of the distinction as its first order of business, and points directly and obviously at (the Global) "Green Parties" several times.
 * 20:07, 25 March 2002 User:AxelBoldt

I don't agree that "a single article should be sufficient" for three reasons:

1. the definition of (the Global) Green Parties is utterly uncontroversial... while they might sometimes disagree on policy or how to agree to agree, they don't disagree on any of their more important principles... the people who add to this article will generally be members of these parties correcting facts, updating history, etc. A tame process.

2. there are an increasing number of "fringe" green party types floating around, and (the Global) Green Parties want desperately to differentiate themselves from them. That's nice, let them do that, but to minimize the number of hacks and trolls here we should make the distinction clearly so that it doesn't fester inside any one article... let the "green Nazis" and "green stoners" and "green fascists" and such all hack "green party" with their own weird doctrine... they will... in fact it was just done today with a link to LNSGP misleadingly added as just another one of many Green Parties. Not. THe one article might have been sufficient until that started to happen....

3. There is already enough complexity in the article describing the Green Parties... if we start to differentiate them from the green parties then we are solving their problems for them. Really, this is their job to do with the public, not our job to do in essays, and the distinctions will change with context... so putting them in a scholarly article is a kind of cancer... especially if anyone can edit it...
 * 20:18, 25 March 2002 User:24.150.61.63


text:
GATT (disambiguation)

GATT or the General Agreement on Tariffs and Trade is a legal agreement between many countries, whose overall purpose was to promote international trade.

Gatt or GATT may also refer to:
 * Gatt (surname)
 * Gatt Gatt the Bat, a nickname given to Mike Gatting, an English cricketer
 * Generic Attribute Profile, a data exchange protocol in Bluetooth Low Energy

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: GATT (disambiguation)


text:
General Agreement on Tariffs and Trade

The General Agreement on Tariffs and Trade (GATT) is a legal agreement between many countries, whose overall purpose was to promote international trade by reducing or eliminating trade barriers such as tariffs or quotas. According to its preamble, its purpose was the "substantial reduction of tariffs and other trade barriers and the elimination of preferences, on a reciprocal and mutually advantageous basis."

The GATT was first discussed during the United Nations Conference on Trade and Employment and was the outcome of the failure of negotiating governments to create the International Trade Organization (ITO). It was signed by 23 nations in Geneva on 30 October 1947, and was applied on a provisional basis 1 January 1948. It remained in effect until 1 January 1995, when the World Trade Organization (WTO) was established after agreement by 123 nations in Marrakesh on 15 April 1994, as part of the Uruguay Round Agreements. The WTO is the successor to the GATT, and the original GATT text (GATT 1947) is still in effect under the WTO framework, subject to the modifications of GATT 1994. Nations that were not party in 1995 to the GATT need to meet the minimum conditions spelled out in specific documents before they can accede; in September 2019, the list contained 36 nations.

The GATT, and its successor the WTO, have succeeded in reducing tariffs. The average tariff levels for the major GATT participants were about 22% in 1947, but were 5% after the Uruguay Round in 1999. Experts attribute part of these tariff changes to GATT and the WTO.

History
The General Agreement on Tariffs and Trade is a multi-national trade treaty. It has been updated in a series of global trade negotiations consisting of nine rounds between 1947 and 1995. Its role in international trade was largely succeeded in 1995 by the World Trade Organization.

During the 1940s, the United States sought to establish a set of post-war multilateral institutions, one of which would be devoted to the reconstruction of world trade. In 1945 and 1946, the U.S. took concrete steps to bring about such an organisation, proposing a conference to negotiate a charter for a trade organisation. The GATT was first conceived at the 1947 United Nations Conference on Trade and Employment (UNCTE), at which the International Trade Organization (ITO) was one of the ideas proposed. It was hoped that the ITO would be run alongside the World Bank and the International Monetary Fund (IMF). More than 50 nations negotiated ITO and organising its founding charter, but after the withdrawal of the United States these negotiations collapsed.

Initial round
Preparatory sessions were held simultaneously at the UNCTE regarding the GATT. After several of these sessions, 23 nations signed the GATT on 30 October 1947 in Geneva, Switzerland. It came into force on 1 January 1948.

Annecy Round: 1949
The second round took place in 1949 in Annecy, France. 13 countries took part in the round. The main focus of the talks was more tariff reductions, around 5,000 in total.

Torquay Round: 1951
The third round occurred in Torquay, England in 1951. Thirty-eight countries took part in the round. 8,700 tariff concessions were made totalling the remaining amount of tariffs to ¾ of the tariffs which were in effect in 1948. The contemporaneous rejection by the U.S. of the Havana Charter signified the establishment of the GATT as a governing world body.

Geneva Round: 1955–56
The fourth round returned to Geneva in 1955 and lasted until May 1956. Twenty-six countries took part in the round. $2.5 billion in tariffs were eliminated or reduced.

Dillon Round: 1960–62
The fifth round occurred once more in Geneva and lasted from 1960 to 1962. The talks were named after U.S. Treasury Secretary and former Under Secretary of State, Douglas Dillon, who first proposed the talks. Twenty-six countries took part in the round. Along with reducing over $4.9 billion in tariffs, it also yielded discussion relating to the creation of the European Economic Community (EEC).

Kennedy Round: 1964–67
The sixth round of GATT multilateral trade negotiations, held from 1964 to 1967. It was named after U.S. President John F. Kennedy in recognition of his support for the reformulation of the United States trade agenda, which resulted in the Trade Expansion Act of 1962. This Act gave the President the widest-ever negotiating authority.

As the Dillon Round went through the laborious process of item-by-item tariff negotiations, it became clear, long before the Round ended, that a more comprehensive approach was needed to deal with the emerging challenges resulting from the formation of the European Economic Community (EEC) and EFTA, as well as Europe's re-emergence as a significant international trader more generally.

Japan's high economic growth rate portended the major role it would play later as an exporter, but the focal point of the Kennedy Round always was the United States–EEC relationship. Indeed, there was an influential American view that saw what became the Kennedy Round as the start of a transatlantic partnership that might ultimately lead to a transatlantic economic community.

To an extent, this view was shared in Europe, but the process of European unification created its own stresses under which the Kennedy Round at times became a secondary focus for the EEC. An example of this was the French veto in January 1963, before the round had even started, on membership by the United Kingdom.

Another was the internal crisis of 1965, which ended in the Luxembourg Compromise. Preparations for the new round were immediately overshadowed by the Chicken War, an early sign of the impact variable levies under the Common Agricultural Policy would eventually have. Some participants in the Round had been concerned that the convening of UNCTAD, scheduled for 1964, would result in further complications, but its impact on the actual negotiations was minimal.

In May 1963 Ministers reached agreement on three negotiating objectives for the round:

 * 1) Measures for the expansion of trade of developing countries as a means of furthering their economic development,
 * 2) Reduction or elimination of tariffs and other barriers to trade, and
 * 3) Measures for access to markets for agricultural and other primary products.

The working hypothesis for the tariff negotiations was a linear tariff cut of 50% with the smallest number of exceptions. A drawn-out argument developed about the trade effects a uniform linear cut would have on the dispersed rates (low and high tariffs quite far apart) of the United States as compared to the much more concentrated rates of the EEC which also tended to be in the lower held of United States tariff rates.

The EEC accordingly argued for an evening-out or harmonisation of peaks and troughs through its cerement, double cart and thirty: ten proposals. Once negotiations had been joined, the lofty working hypothesis was soon undermined. The special-structure countries (Australia, Canada, New Zealand and South Africa), so called because their exports were dominated by raw materials and other primary commodities, negotiated their tariff reductions entirely through the item-by-item method.

In the end, the result was an average 35% reduction in tariffs, except for textiles, chemicals, steel and other sensitive products; plus a 15% to 18% reduction in tariffs for agricultural and food products. In addition, the negotiations on chemicals led to a provisional agreement on the abolition of the American Selling Price (ASP). This was a method of valuing some chemicals used by the noted States for the imposition of import duties which gave domestic manufacturers a much higher level of protection than the tariff schedule indicated.

However, this part of the outcome was disallowed by Congress, and the American Selling Price was not abolished until Congress adopted the results of the Tokyo Round. The results on agriculture overall were poor. The most notable achievement was agreement on a Memorandum of Agreement on Basic Elements for the Negotiation of a World Grants Arrangement, which eventually was rolled into a new International Grains Arrangement.

The EEC claimed that for it the main result of the negotiations on agriculture was that they "greatly helped to define its own common policy". The developing countries, who played a minor role throughout the negotiations in this round, benefited nonetheless from substantial tariff cuts particularly in non-agricultural items of interest to them.

Their main achievement at the time, however, was seen to be the adoption of Part IV of the GATT, which absolved them from according reciprocity to developed countries in trade negotiations. In the view of many developing countries, this was a direct result of the call at UNCTAD I for a better trade deal for them.

There has been argument ever since whether this symbolic gesture was a victory for them, or whether it ensured their exclusion in the future from meaningful participation in the multilateral trading system. On the other hand, there was no doubt that the extension of the Long-Term Arrangement Regarding International Trade in Cotton Textiles, which later became the Multi-Fiber Arrangement, for three years until 1970 led to the longer-term impairment of export opportunities for developing countries.

Another outcome of the Kennedy Round was the adoption of an Anti-dumping Code, which gave more precise guidance on the implementation of Article VI of the GATT. In particular, it sought to ensure speedy and fair investigations, and it imposed limits on the retrospective application of anti-dumping measures.

Kennedy Round took place from 1962 to 1967. $40 billion in tariffs were eliminated or reduced.

Tokyo Round: 1973–79
Reduced tariffs and established new regulations aimed at controlling the proliferation of non-tariff barriers and voluntary export restrictions. 102 countries took part in the round. Concessions were made on $19 billion worth of trade.

Formation of Quadrilateral Group: 1981
The Quadrilateral Group was formed in 1982 by the European Union, the United States, Japan and Canada, to influence the GATT.

Uruguay Round: 1986–94
The Uruguay Round began in 1986. It was the most ambitious round to date, as of 1986, hoping to expand the competence of the GATT to important new areas such as services, capital, intellectual property, textiles, and agriculture. 123 countries took part in the round. The Uruguay Round was also the first set of multilateral trade negotiations in which developing countries had played an active role.

Agriculture was essentially exempted from previous agreements as it was given special status in the areas of import quotas and export subsidies, with only mild caveats. However, by the time of the Uruguay round, many countries considered the exception of agriculture to be sufficiently glaring that they refused to sign a new deal without some movement on agricultural products. These fourteen countries came to be known as the "Cairns Group", and included mostly small and medium-sized agricultural exporters such as Australia, Brazil, Canada, Indonesia, and New Zealand.

The Agreement on Agriculture of the Uruguay Round continues to be the most substantial trade liberalisation agreement in agricultural products in the history of trade negotiations. The goals of the agreement were to improve market access for agricultural products, reduce domestic support of agriculture in the form of price-distorting subsidies and quotas, eliminate over time export subsidies on agricultural products and to harmonise to the extent possible sanitary and phytosanitary measures between member countries.

World Trade Organization
In 1993, the GATT was updated ('GATT 1994') to include new obligations upon its signatories. One of the most significant changes was the creation of the World Trade Organization (WTO). The 76 existing GATT members and the European Communities became the founding members of the WTO on 1 January 1995. The other 51 GATT members rejoined the WTO in the following two years (the last being Congo in 1997). Since the founding of the WTO, 33 new non-GATT members have joined and 22 are currently negotiating membership. There are a total of 164 member countries in the WTO, with Liberia and Afghanistan being the newest members as of 2018.

Of the original GATT members, Syria, Lebanon and the SFR Yugoslavia have not rejoined the WTO. Since FR Yugoslavia (renamed as Serbia and Montenegro and with membership negotiations later split in two), is not recognised as a direct SFRY successor state; therefore, its application is considered a new (non-GATT) one. The General Council of WTO, on 4 May 2010, agreed to establish a working party to examine the request of Syria for WTO membership. The contracting parties who founded the WTO ended official agreement of the "GATT 1947" terms on 31 December 1995. Montenegro became a member in 2012, while Serbia is in the decision stage of the negotiations and is expected to become a member of the WTO in the future.

Whilst GATT was a set of rules agreed upon by nations, the WTO is an intergovernmental organisation with its own headquarters and staff, and its scope includes both traded goods and trade within the service sector and intellectual property rights. Although it was designed to serve multilateral agreements, during several rounds of GATT negotiations (particularly the Tokyo Round) plurilateral agreements created selective trading and caused fragmentation among members. WTO arrangements are generally a multilateral agreement settlement mechanism of GATT.

Effects on trade liberalisation
The average tariff levels for the major GATT participants were about 22 per cent in 1947. As a result of the first negotiating rounds, tariffs were reduced in the GATT core of the United States, United Kingdom, Canada, and Australia, relative to other contracting parties and non-GATT participants. By the Kennedy round (1962–67), the average tariff levels of GATT participants were about 15%. After the Uruguay Round, tariffs were under 5%.

In addition to facilitating applied tariff reductions, the early GATT's contribution to trade liberalisation "include binding the negotiated tariff reductions for an extended period (made more permanent in 1955), establishing the generality of non-discrimination through most favoured nation (MFN) treatment and national treatment status, ensuring increased transparency of trade policy measures, and providing a forum for future negotiations and for the peaceful resolution of bilateral disputes. All of these elements contributed to the rationalization of trade policy and the reduction of trade barriers and policy uncertainty."

According to Dartmouth economic historian Douglas Irwin,

"The prosperity of the world economy over the past half century owes a great deal to the growth of world trade which, in turn, is partly the result of farsighted officials who created the GATT. They established a set of procedures giving stability to the trade-policy environment and thereby facilitating the rapid growth of world trade. With the long run in view, the original GATT conferees helped put the world economy on a sound foundation and thereby improved the livelihood of hundreds of millions of people around the world."

Article 24
Following the United Kingdom's vote to withdraw from the European Union, supporters of leaving the EU suggested that Article 24, paragraph 5B of the treaty could be used to maintain a "standstill" in trading conditions between the UK and the EU in the event of the UK leaving the EU without a trade deal, hence preventing the introduction of tariffs. According to proponents of this approach, it could be used to implement an interim agreement pending negotiation of a final agreement lasting up to ten years.

This claim formed the basis of the so-called "Malthouse compromise" between Conservative party factions as to how to replace the withdrawal agreement. However, this plan was rejected by parliament. The claim that Article 24 might be used was also adopted by Boris Johnson during his 2019 campaign to lead the Conservative Party.

The claim that Article 24 might be used in this way has been criticised by Mark Carney, Liam Fox and others as being unrealistic given the requirement in paragraph 5c of the treaty that there be an agreement between the parties for paragraph 5b to be of use as, in the event of a "no-deal" scenario, there would be no agreement. Moreover, critics of the GATT 24 approach point out that services would not be covered by such an arrangement.

title: General Agreement on Tariffs and Trade


text:
G protein-coupled receptor

G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily related proteins that are cell surface receptors that detect molecules outside the cell and activate cellular responses. They are coupled with G proteins. They pass through the cell membrane seven times in the form of six loops (three extracellular loops interacting with ligand molecules, three intracellular loops interacting with G proteins, an N-terminal extracellular region and a C-terminal intracellular region ) of amino acid residues, which is why they are sometimes referred to as seven-transmembrane receptors. Ligands can bind either to the extracellular N-terminus and loops (e.g. glutamate receptors) or to the binding site within transmembrane helices (rhodopsin-like family). They are all activated by agonists, although a spontaneous auto-activation of an empty receptor has also been observed.

G protein-coupled receptors are found only in eukaryotes, including yeast, and choanoflagellates. The ligands that bind and activate these receptors include light-sensitive compounds, odors, pheromones, hormones, and neurotransmitters, and vary in size from small molecules to peptides to large proteins. G protein-coupled receptors are involved in many diseases.

There are two principal signal transduction pathways involving the G protein-coupled receptors: When a ligand binds to the GPCR it causes a conformational change in the GPCR, which allows it to act as a guanine nucleotide exchange factor (GEF). The GPCR can then activate an associated G protein by exchanging the GDP bound to the G protein for a GTP. The G protein's α subunit, together with the bound GTP, can then dissociate from the β and γ subunits to further affect intracellular signaling proteins or target functional proteins directly depending on the α subunit type (Gαs, Gαi/o, Gαq/11, Gα12/13).
 * the cAMP signal pathway and
 * the phosphatidylinositol signal pathway.

GPCRs are an important drug target and approximately 34% of all Food and Drug Administration (FDA) approved drugs target 108 members of this family. The global sales volume for these drugs is estimated to be 180 billion US dollars. It is estimated that GPCRs are targets for about 50% of drugs currently on the market, mainly due to their involvement in signaling pathways related to many diseases i.e. mental, metabolic including endocrinological disorders, immunological including viral infections, cardiovascular, inflammatory, senses disorders, and cancer. The long ago discovered association between GPCRs and many endogenous and exogenous substances, resulting in e.g. analgesia, is another dynamically developing field of the pharmaceutical research.

History and significance
With the determination of the first structure of the complex between a G-protein coupled receptor (GPCR) and a G-protein trimer (Gαβγ) in 2011 a new chapter of GPCR research was opened for structural investigations of global switches with more than one protein being investigated. The previous breakthroughs involved determination of the crystal structure of the first GPCR, rhodopsin, in 2000 and the crystal structure of the first GPCR with a diffusible ligand (β2AR) in 2007. The way in which the seven transmembrane helices of a GPCR are arranged into a bundle was suspected based on the low-resolution model of frog rhodopsin from cryogenic electron microscopy studies of the two-dimensional crystals. The crystal structure of rhodopsin, that came up three years later, was not a surprise apart from the presence of an additional cytoplasmic helix H8 and a precise location of a loop covering retinal binding site. However, it provided a scaffold which was hoped to be a universal template for homology modeling and drug design for other GPCRs – a notion that proved to be too optimistic.

Seven years later, the crystallization of β2-adrenergic receptor (β2AR) with a diffusible ligand brought surprising results because it revealed quite a different shape of the receptor extracellular side than that of rhodopsin. This area is important because it is responsible for the ligand binding and is targeted by many drugs. Moreover, the ligand binding site was much more spacious than in the rhodopsin structure and was open to the exterior. In the other receptors crystallized shortly afterwards the binding side was even more easily accessible to the ligand. New structures complemented with biochemical investigations uncovered mechanisms of action of molecular switches which modulate the structure of the receptor leading to activation states for agonists or to complete or partial inactivation states for inverse agonists.

The 2012 Nobel Prize in Chemistry was awarded to Brian Kobilka and Robert Lefkowitz for their work that was "crucial for understanding how G protein-coupled receptors function". There have been at least seven other Nobel Prizes awarded for some aspect of G protein–mediated signaling. As of 2012, two of the top ten global best-selling drugs (Advair Diskus and Abilify) act by targeting G protein-coupled receptors.

Classification

The exact size of the GPCR superfamily is unknown, but at least 831 different human genes (or about 4% of the entire protein-coding genome) have been predicted to code for them from genome sequence analysis. Although numerous classification schemes have been proposed, the superfamily was classically divided into three main classes (A, B, and C) with no detectable shared sequence homology between classes.

The largest class by far is class A, which accounts for nearly 85% of the GPCR genes. Of class A GPCRs, over half of these are predicted to encode olfactory receptors, while the remaining receptors are liganded by known endogenous compounds or are classified as orphan receptors. Despite the lack of sequence homology between classes, all GPCRs have a common structure and mechanism of signal transduction. The very large rhodopsin A group has been further subdivided into 19 subgroups (A1-A19).

According to the classical A-F system, GPCRs can be grouped into six classes based on sequence homology and functional similarity:
 * Class A (or 1) (Rhodopsin-like)
 * Class B (or 2) (Secretin receptor family)
 * Class C (or 3) (Metabotropic glutamate/pheromone)
 * Class D (or 4) (Fungal mating pheromone receptors)
 * Class E (or 5) (Cyclic AMP receptors)
 * Class F (or 6) (Frizzled/Smoothened)

More recently, an alternative classification system called GRAFS (Glutamate, Rhodopsin, Adhesion, Frizzled/Taste2, Secretin) has been proposed for vertebrate GPCRs. They correspond to classical classes C, A, B2, F, and B.

An early study based on available DNA sequence suggested that the human genome encodes roughly 750 G protein-coupled receptors, about 350 of which detect hormones, growth factors, and other endogenous ligands. Approximately 150 of the GPCRs found in the human genome have unknown functions.

Some web-servers and bioinformatics prediction methods have been used for predicting the classification of GPCRs according to their amino acid sequence alone, by means of the pseudo amino acid composition approach.

Physiological roles
GPCRs are involved in a wide variety of physiological processes. Some examples of their physiological roles include:
 * 1) The visual sense: The opsins use a photoisomerization reaction to translate electromagnetic radiation into cellular signals. Rhodopsin, for example, uses the conversion of 11-cis-retinal to all-trans-retinal for this purpose.
 * 2) The gustatory sense (taste): GPCRs in taste cells mediate release of gustducin in response to bitter-, umami- and sweet-tasting substances.
 * 3) The sense of smell: Receptors of the olfactory epithelium bind odorants (olfactory receptors) and pheromones (vomeronasal receptors)
 * 4) Behavioral and mood regulation: Receptors in the mammalian brain bind several different neurotransmitters, including serotonin, dopamine, histamine, GABA, and glutamate
 * 5) Regulation of immune system activity and inflammation: chemokine receptors bind ligands that mediate intercellular communication between cells of the immune system; receptors such as histamine receptors bind inflammatory mediators and engage target cell types in the inflammatory response. GPCRs are also involved in immune-modulation, e. g. regulating interleukin induction or suppressing TLR-induced immune responses from T cells.
 * 6) Autonomic nervous system transmission: Both the sympathetic and parasympathetic nervous systems are regulated by GPCR pathways, responsible for control of many automatic functions of the body such as blood pressure, heart rate, and digestive processes
 * 7) Cell density sensing: A novel GPCR role in regulating cell density sensing.
 * 8) Homeostasis modulation (e.g., water balance).
 * 9) Involved in growth and metastasis of some types of tumors.
 * 10) Used in the endocrine system for peptide and amino-acid derivative hormones that bind to GCPRs on the cell membrane of a target cell. This activates cAMP, which in turn activates several kinases, allowing for a cellular response, such as transcription.

Receptor structure
GPCRs are integral membrane proteins that possess seven membrane-spanning domains or transmembrane helices. The extracellular parts of the receptor can be glycosylated. These extracellular loops also contain two highly conserved cysteine residues that form disulfide bonds to stabilize the receptor structure. Some seven-transmembrane helix proteins (channelrhodopsin) that resemble GPCRs may contain ion channels, within their protein.

In 2000, the first crystal structure of a mammalian GPCR, that of bovine rhodopsin, was solved. In 2007, the first structure of a human GPCR was solved  This human β2-adrenergic receptor GPCR structure proved highly similar to the bovine rhodopsin. The structures of activated or agonist-bound GPCRs have also been determined. These structures indicate how ligand binding at the extracellular side of a receptor leads to conformational changes in the cytoplasmic side of the receptor. The biggest change is an outward movement of the cytoplasmic part of the 5th and 6th transmembrane helix (TM5 and TM6). The structure of activated beta-2 adrenergic receptor in complex with Gs confirmed that the Gα binds to a cavity created by this movement.

GPCRs exhibit a similar structure to some other proteins with seven transmembrane domains, such as microbial rhodopsins and adiponectin receptors 1 and 2 (ADIPOR1 and ADIPOR2). However, these 7TMH (7-transmembrane helices) receptors and channels do not associate with G proteins. In addition, ADIPOR1 and ADIPOR2 are oriented oppositely to GPCRs in the membrane (i.e. GPCRs usually have an extracellular N-terminus, cytoplasmic C-terminus, whereas ADIPORs are inverted).

Structure–function relationships
In terms of structure, GPCRs are characterized by an extracellular N-terminus, followed by seven transmembrane (7-TM) α-helices (TM-1 to TM-7) connected by three intracellular (IL-1 to IL-3) and three extracellular loops (EL-1 to EL-3), and finally an intracellular C-terminus. The GPCR arranges itself into a tertiary structure resembling a barrel, with the seven transmembrane helices forming a cavity within the plasma membrane that serves a ligand-binding domain that is often covered by EL-2. Ligands may also bind elsewhere, however, as is the case for bulkier ligands (e.g., proteins or large peptides), which instead interact with the extracellular loops, or, as illustrated by the class C metabotropic glutamate receptors (mGluRs), the N-terminal tail. The class C GPCRs are distinguished by their large N-terminal tail, which also contains a ligand-binding domain. Upon glutamate-binding to an mGluR, the N-terminal tail undergoes a conformational change that leads to its interaction with the residues of the extracellular loops and TM domains. The eventual effect of all three types of agonist-induced activation is a change in the relative orientations of the TM helices (likened to a twisting motion) leading to a wider intracellular surface and "revelation" of residues of the intracellular helices and TM domains crucial to signal transduction function (i.e., G-protein coupling). Inverse agonists and antagonists may also bind to a number of different sites, but the eventual effect must be prevention of this TM helix reorientation.

The structure of the N- and C-terminal tails of GPCRs may also serve important functions beyond ligand-binding. For example, The C-terminus of M3 muscarinic receptors is sufficient, and the six-amino-acid polybasic (KKKRRK) domain in the C-terminus is necessary for its preassembly with Gq proteins. In particular, the C-terminus often contains serine (Ser) or threonine (Thr) residues that, when phosphorylated, increase the affinity of the intracellular surface for the binding of scaffolding proteins called β-arrestins (β-arr). Once bound, β-arrestins both sterically prevent G-protein coupling and may recruit other proteins, leading to the creation of signaling complexes involved in extracellular-signal regulated kinase (ERK) pathway activation or receptor endocytosis (internalization). As the phosphorylation of these Ser and Thr residues often occurs as a result of GPCR activation, the β-arr-mediated G-protein-decoupling and internalization of GPCRs are important mechanisms of desensitization. In addition, internalized "mega-complexes" consisting of a single GPCR, β-arr(in the tail conformation), and heterotrimeric G protein exist and may account for protein signaling from endosomes.

A final common structural theme among GPCRs is palmitoylation of one or more sites of the C-terminal tail or the intracellular loops. Palmitoylation is the covalent modification of cysteine (Cys) residues via addition of hydrophobic acyl groups, and has the effect of targeting the receptor to cholesterol- and sphingolipid-rich microdomains of the plasma membrane called lipid rafts. As many of the downstream transducer and effector molecules of GPCRs (including those involved in negative feedback pathways) are also targeted to lipid rafts, this has the effect of facilitating rapid receptor signaling.

GPCRs respond to extracellular signals mediated by a huge diversity of agonists, ranging from proteins to biogenic amines to protons, but all transduce this signal via a mechanism of G-protein coupling. This is made possible by a guanine-nucleotide exchange factor (GEF) domain primarily formed by a combination of IL-2 and IL-3 along with adjacent residues of the associated TM helices.

Mechanism

The G protein-coupled receptor is activated by an external signal in the form of a ligand or other signal mediator. This creates a conformational change in the receptor, causing activation of a G protein. Further effect depends on the type of G protein. G proteins are subsequently inactivated by GTPase activating proteins, known as RGS proteins.

Ligand binding
GPCRs include one or more receptors for the following ligands: sensory signal mediators (e.g., light and olfactory stimulatory molecules); adenosine, bombesin, bradykinin, endothelin, γ-aminobutyric acid (GABA), hepatocyte growth factor (HGF), melanocortins, neuropeptide Y, opioid peptides, opsins, somatostatin, GH, tachykinins, members of the vasoactive intestinal peptide family, and vasopressin; biogenic amines (e.g., dopamine, epinephrine, norepinephrine, histamine, serotonin, and melatonin); glutamate (metabotropic effect); glucagon; acetylcholine (muscarinic effect); chemokines; lipid mediators of inflammation (e.g., prostaglandins, prostanoids, platelet-activating factor, and leukotrienes); peptide hormones (e.g., calcitonin, C5a anaphylatoxin, follicle-stimulating hormone [FSH], gonadotropin-releasing hormone [GnRH], neurokinin, thyrotropin-releasing hormone [TRH], and oxytocin); and endocannabinoids.

GPCRs that act as receptors for stimuli that have not yet been identified are known as orphan receptors.

However, in contrast to other types of receptors that have been studied, wherein ligands bind externally to the membrane, the ligands of GPCRs typically bind within the transmembrane domain. However, protease-activated receptors are activated by cleavage of part of their extracellular domain.

Conformational change

The transduction of the signal through the membrane by the receptor is not completely understood. It is known that in the inactive state, the GPCR is bound to a heterotrimeric G protein complex. Binding of an agonist to the GPCR results in a conformational change in the receptor that is transmitted to the bound Gα subunit of the heterotrimeric G protein via protein domain dynamics. The activated Gα subunit exchanges GTP in place of GDP which in turn triggers the dissociation of Gα subunit from the Gβγ dimer and from the receptor. The dissociated Gα and Gβγ subunits interact with other intracellular proteins to continue the signal transduction cascade while the freed GPCR is able to rebind to another heterotrimeric G protein to form a new complex that is ready to initiate another round of signal transduction.

It is believed that a receptor molecule exists in a conformational equilibrium between active and inactive biophysical states. The binding of ligands to the receptor may shift the equilibrium toward the active receptor states. Three types of ligands exist: Agonists are ligands that shift the equilibrium in favour of active states; inverse agonists are ligands that shift the equilibrium in favour of inactive states; and neutral antagonists are ligands that do not affect the equilibrium. It is not yet known how exactly the active and inactive states differ from each other.

G-protein activation/deactivation cycle

When the receptor is inactive, the GEF domain may be bound to an also inactive α-subunit of a heterotrimeric G-protein. These "G-proteins" are a trimer of α, β, and γ subunits (known as Gα, Gβ, and Gγ, respectively) that is rendered inactive when reversibly bound to Guanosine diphosphate (GDP) (or, alternatively, no guanine nucleotide) but active when bound to guanosine triphosphate (GTP). Upon receptor activation, the GEF domain, in turn, allosterically activates the G-protein by facilitating the exchange of a molecule of GDP for GTP at the G-protein's α-subunit. The cell maintains a 10:1 ratio of cytosolic GTP:GDP so exchange for GTP is ensured. At this point, the subunits of the G-protein dissociate from the receptor, as well as each other, to yield a Gα-GTP monomer and a tightly interacting Gβγ dimer, which are now free to modulate the activity of other intracellular proteins. The extent to which they may diffuse, however, is limited due to the palmitoylation of Gα and the presence of an isoprenoid moiety that has been covalently added to the C-termini of Gγ.

Because Gα also has slow GTP→GDP hydrolysis capability, the inactive form of the α-subunit (Gα-GDP) is eventually regenerated, thus allowing reassociation with a Gβγ dimer to form the "resting" G-protein, which can again bind to a GPCR and await activation. The rate of GTP hydrolysis is often accelerated due to the actions of another family of allosteric modulating proteins called regulators of G-protein signaling, or RGS proteins, which are a type of GTPase-activating protein, or GAP. In fact, many of the primary effector proteins (e.g., adenylate cyclases) that become activated/inactivated upon interaction with Gα-GTP also have GAP activity. Thus, even at this early stage in the process, GPCR-initiated signaling has the capacity for self-termination.

Crosstalk
GPCRs downstream signals have been shown to possibly interact with integrin signals, such as FAK. Integrin signaling will phosphorylate FAK, which can then decrease GPCR Gαs activity.

Signaling
If a receptor in an active state encounters a G protein, it may activate it. Some evidence suggests that receptors and G proteins are actually pre-coupled. For example, binding of G proteins to receptors affects the receptor's affinity for ligands. Activated G proteins are bound to GTP.

Further signal transduction depends on the type of G protein. The enzyme adenylate cyclase is an example of a cellular protein that can be regulated by a G protein, in this case the G protein Gs. Adenylate cyclase activity is activated when it binds to a subunit of the activated G protein. Activation of adenylate cyclase ends when the G protein returns to the GDP-bound state.

Adenylate cyclases (of which 9 membrane-bound and one cytosolic forms are known in humans) may also be activated or inhibited in other ways (e.g., Ca2+/calmodulin binding), which can modify the activity of these enzymes in an additive or synergistic fashion along with the G proteins.

The signaling pathways activated through a GPCR are limited by the primary sequence and tertiary structure of the GPCR itself but ultimately determined by the particular conformation stabilized by a particular ligand, as well as the availability of transducer molecules. Currently, GPCRs are considered to utilize two primary types of transducers: G-proteins and β-arrestins. Because β-arr's have high affinity only to the phosphorylated form of most GPCRs (see above or below), the majority of signaling is ultimately dependent upon G-protein activation. However, the possibility for interaction does allow for G-protein-independent signaling to occur.

G-protein-dependent signaling
There are three main G-protein-mediated signaling pathways, mediated by four sub-classes of G-proteins distinguished from each other by sequence homology (Gαs, Gαi/o, Gαq/11, and Gα12/13). Each sub-class of G-protein consists of multiple proteins, each the product of multiple genes or splice variations that may imbue them with differences ranging from subtle to distinct with regard to signaling properties, but in general they appear reasonably grouped into four classes. Because the signal transducing properties of the various possible βγ combinations do not appear to radically differ from one another, these classes are defined according to the isoform of their α-subunit.

While most GPCRs are capable of activating more than one Gα-subtype, they also show a preference for one subtype over another. When the subtype activated depends on the ligand that is bound to the GPCR, this is called functional selectivity (also known as agonist-directed trafficking, or conformation-specific agonism). However, the binding of any single particular agonist may also initiate activation of multiple different G-proteins, as it may be capable of stabilizing more than one conformation of the GPCR's GEF domain, even over the course of a single interaction. In addition, a conformation that preferably activates one isoform of Gα may activate another if the preferred is less available. Furthermore, feedback pathways may result in receptor modifications (e.g., phosphorylation) that alter the G-protein preference. Regardless of these various nuances, the GPCR's preferred coupling partner is usually defined according to the G-protein most obviously activated by the endogenous ligand under most physiological or experimental conditions.

Gα signaling

 * 1) The effector of both the Gαs and Gαi/o pathways is the cyclic-adenosine monophosphate (cAMP)-generating enzyme adenylate cyclase, or AC. While there are ten different AC gene products in mammals, each with subtle differences in tissue distribution or function, all catalyze the conversion of cytosolic adenosine triphosphate (ATP) to cAMP, and all are directly stimulated by G-proteins of the Gαs class. In contrast, however, interaction with Gα subunits of the Gαi/o type inhibits AC from generating cAMP. Thus, a GPCR coupled to Gαs counteracts the actions of a GPCR coupled to Gαi/o, and vice versa. The level of cytosolic cAMP may then determine the activity of various ion channels as well as members of the ser/thr-specific protein kinase A (PKA) family. Thus cAMP is considered a second messenger and PKA a secondary effector.
 * 2) The effector of the Gαq/11 pathway is phospholipase C-β (PLCβ), which catalyzes the cleavage of membrane-bound phosphatidylinositol 4,5-bisphosphate (PIP2) into the second messengers inositol (1,4,5) trisphosphate (IP3) and diacylglycerol (DAG). IP3 acts on IP3 receptors found in the membrane of the endoplasmic reticulum (ER) to elicit Ca2+ release from the ER, while DAG diffuses along the plasma membrane where it may activate any membrane localized forms of a second ser/thr kinase called protein kinase C (PKC). Since many isoforms of PKC are also activated by increases in intracellular Ca2+, both these pathways can also converge on each other to signal through the same secondary effector. Elevated intracellular Ca2+ also binds and allosterically activates proteins called calmodulins, which in turn tosolic small GTPase, Rho. Once bound to GTP, Rho can then go on to activate various proteins responsible for cytoskeleton regulation such as Rho-kinase (ROCK). Most GPCRs that couple to Gα12/13 also couple to other sub-classes, often Gαq/11.

Gβγ signaling
The above descriptions ignore the effects of Gβγ–signalling, which can also be important, in particular in the case of activated Gαi/o-coupled GPCRs. The primary effectors of Gβγ are various ion channels, such as G-protein-regulated inwardly rectifying K+ channels (GIRKs), P/Q- and N-type voltage-gated Ca2+ channels, as well as some isoforms of AC and PLC, along with some phosphoinositide-3-kinase (PI3K) isoforms.

G-protein-independent signaling
Although they are classically thought of working only together, GPCRs may signal through G-protein-independent mechanisms, and heterotrimeric G-proteins may play functional roles independent of GPCRs. GPCRs may signal independently through many proteins already mentioned for their roles in G-protein-dependent signaling such as β-arrs, GRKs, and Srcs. Such signaling has been shown to be physiologically relevant, for example, β-arrestin signaling mediated by the chemokine receptor CXCR3 was necessary for full efficacy chemotaxis of activated T cells. In addition, further scaffolding proteins involved in subcellular localization of GPCRs (e.g., PDZ-domain-containing proteins) may also act as signal transducers. Most often the effector is a member of the MAPK family.

Examples
In the late 1990s, evidence began accumulating to suggest that some GPCRs are able to signal without G proteins. The ERK2 mitogen-activated protein kinase, a key signal transduction mediator downstream of receptor activation in many pathways, has been shown to be activated in response to cAMP-mediated receptor activation in the slime mold D. discoideum despite the absence of the associated G protein α- and β-subunits.

In mammalian cells, the much-studied β2-adrenoceptor has been demonstrated to activate the ERK2 pathway after arrestin-mediated uncoupling of G-protein-mediated signaling. Therefore, it seems likely that some mechanisms previously believed related purely to receptor desensitisation are actually examples of receptors switching their signaling pathway, rather than simply being switched off.

In kidney cells, the bradykinin receptor B2 has been shown to interact directly with a protein tyrosine phosphatase. The presence of a tyrosine-phosphorylated ITIM (immunoreceptor tyrosine-based inhibitory motif) sequence in the B2 receptor is necessary to mediate this interaction and subsequently the antiproliferative effect of bradykinin.

GPCR-independent signaling by heterotrimeric G-proteins
Although it is a relatively immature area of research, it appears that heterotrimeric G-proteins may also take part in non-GPCR signaling. There is evidence for roles as signal transducers in nearly all other types of receptor-mediated signaling, including integrins, receptor tyrosine kinases (RTKs), cytokine receptors (JAK/STATs), as well as modulation of various other "accessory" proteins such as GEFs, guanine-nucleotide dissociation inhibitors (GDIs) and protein phosphatases. There may even be specific proteins of these classes whose primary function is as part of GPCR-independent pathways, termed activators of G-protein signalling (AGS). Both the ubiquity of these interactions and the importance of Gα vs. Gβγ subunits to these processes are still unclear.

Details of cAMP and PIP2 pathways
There are two principal signal transduction pathways involving the G protein-linked receptors: the cAMP signal pathway and the phosphatidylinositol signal pathway.

cAMP signal pathway
The cAMP signal transduction contains five main characters: stimulative hormone receptor (Rs) or inhibitory hormone receptor (Ri); stimulative regulative G-protein (Gs) or inhibitory regulative G-protein (Gi); adenylyl cyclase; protein kinase A (PKA); and cAMP phosphodiesterase.

Stimulative hormone receptor (Rs) is a receptor that can bind with stimulative signal molecules, while inhibitory hormone receptor (Ri) is a receptor that can bind with inhibitory signal molecules.

Stimulative regulative G-protein is a G-protein linked to stimulative hormone receptor (Rs), and its α subunit upon activation could stimulate the activity of an enzyme or other intracellular metabolism. On the contrary, inhibitory regulative G-protein is linked to an inhibitory hormone receptor, and its α subunit upon activation could inhibit the activity of an enzyme or other intracellular metabolism.

Adenylyl cyclase is a 12-transmembrane glycoprotein that catalyzes the conversion of ATP to cAMP with the help of cofactor Mg2+ or Mn2+. The cAMP produced is a second messenger in cellular metabolism and is an allosteric activator of protein kinase A.

Protein kinase A is an important enzyme in cell metabolism due to its ability to regulate cell metabolism by phosphorylating specific committed enzymes in the metabolic pathway. It can also regulate specific gene expression, cellular secretion, and membrane permeability. The protein enzyme contains two catalytic subunits and two regulatory subunits. When there is no cAMP，the complex is inactive. When cAMP binds to the regulatory subunits, their conformation is altered, causing the dissociation of the regulatory subunits, which activates protein kinase A and allows further biological effects.

These signals then can be terminated by cAMP phosphodiesterase, which is an enzyme that degrades cAMP to 5'-AMP and inactivates protein kinase A.

Phosphatidylinositol signal pathway
In the phosphatidylinositol signal pathway, the extracellular signal molecule binds with the G-protein receptor (Gq) on the cell surface and activates phospholipase C, which is located on the plasma membrane. The lipase hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into two second messengers: inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 binds with the IP3 receptor in the membrane of the smooth endoplasmic reticulum and mitochondria to open Ca2+ channels. DAG helps activate protein kinase C (PKC), which phosphorylates many other proteins, changing their catalytic activities, leading to cellular responses.

The effects of Ca2+ are also remarkable: it cooperates with DAG in activating PKC and can activate the CaM kinase pathway, in which calcium-modulated protein calmodulin (CaM) binds Ca2+, undergoes a change in conformation, and activates CaM kinase II, which has unique ability to increase its binding affinity to CaM by autophosphorylation, making CaM unavailable for the activation of other enzymes. The kinase then phosphorylates target enzymes, regulating their activities. The two signal pathways are connected together by Ca2+-CaM, which is also a regulatory subunit of adenylyl cyclase and phosphodiesterase in the cAMP signal pathway.

Receptor regulation
GPCRs become desensitized when exposed to their ligand for a long period of time. There are two recognized forms of desensitization: 1) homologous desensitization, in which the activated GPCR is downregulated; and 2) heterologous desensitization, wherein the activated GPCR causes downregulation of a different GPCR. The key reaction of this downregulation is the phosphorylation of the intracellular (or cytoplasmic) receptor domain by protein kinases.

Phosphorylation by cAMP-dependent protein kinases
Cyclic AMP-dependent protein kinases (protein kinase A) are activated by the signal chain coming from the G protein (that was activated by the receptor) via adenylate cyclase and cyclic AMP (cAMP). In a feedback mechanism, these activated kinases phosphorylate the receptor. The longer the receptor remains active the more kinases are activated and the more receptors are phosphorylated. In β2-adrenoceptors, this phosphorylation results in the switching of the coupling from the Gs class of G-protein to the Gi class. cAMP-dependent PKA mediated phosphorylation can cause heterologous desensitisation in receptors other than those activated.

Phosphorylation by GRKs
The G protein-coupled receptor kinases (GRKs) are protein kinases that phosphorylate only active GPCRs. G-protein-coupled receptor kinases (GRKs) are key modulators of G-protein-coupled receptor (GPCR) signaling. They constitute a family of seven mammalian serine-threonine protein kinases that phosphorylate agonist-bound receptor. GRKs-mediated receptor phosphorylation rapidly initiates profound impairment of receptor signaling and desensitization. Activity of GRKs and subcellular targeting is tightly regulated by interaction with receptor domains, G protein subunits, lipids, anchoring proteins and calcium-sensitive proteins.

Phosphorylation of the receptor can have two consequences:

 * 1) Translocation: The receptor is, along with the part of the membrane it is embedded in, brought to the inside of the cell, where it is dephosphorylated within the acidic vesicular environment and then brought back. This mechanism is used to regulate long-term exposure, for example, to a hormone, by allowing resensitisation to follow desensitisation. Alternatively, the receptor may undergo lysozomal degradation, or remain internalised, where it is thought to participate in the initiation of signalling events, the nature of which depending on the internalised vesicle's subcellular localisation.
 * 2) Arrestin linking: The phosphorylated receptor can be linked to arrestin molecules that prevent it from binding (and activating) G proteins, in effect switching it off for a short period of time. This mechanism is used, for example, with rhodopsin in retina cells to compensate for exposure to bright light. In many cases, arrestin's binding to the receptor is a prerequisite for translocation. For example, beta-arrestin bound to β2-adrenoreceptors acts as an adaptor for binding with clathrin, and with the beta-subunit of AP2 (clathrin adaptor molecules); thus, the arrestin here acts as a scaffold assembling the components needed for clathrin-mediated endocytosis of β2-adrenoreceptors.

Mechanisms of GPCR signal termination
As mentioned above, G-proteins may terminate their own activation due to their intrinsic GTP→GDP hydrolysis capability. However, this reaction proceeds at a slow rate (≈0.02 times/sec) and, thus, it would take around 50 seconds for any single G-protein to deactivate if other factors did not come into play. Indeed, there are around 30 isoforms of RGS proteins that, when bound to Gα through their GAP domain, accelerate the hydrolysis rate to ≈30 times/sec. This 1500-fold increase in rate allows for the cell to respond to external signals with high speed, as well as spatial resolution due to limited amount of second messenger that can be generated and limited distance a G-protein can diffuse in 0.03 seconds. For the most part, the RGS proteins are promiscuous in their ability to deactivate G-proteins, while which RGS is involved in a given signaling pathway seems more determined by the tissue and GPCR involved than anything else. In addition, RGS proteins have the additional function of increasing the rate of GTP-GDP exchange at GPCRs, (i.e., as a sort of co-GEF) further contributing to the time resolution of GPCR signaling.

In addition, the GPCR may be desensitized itself. This can occur as:

 * 1) a direct result of ligand occupation, wherein the change in conformation allows recruitment of GPCR-Regulating Kinases (GRKs), which go on to phosphorylate various serine/threonine residues of IL-3 and the C-terminal tail. Upon GRK phosphorylation, the GPCR's affinity for β-arrestin (β-arrestin-1/2 in most tissues) is increased, at which point β-arrestin may bind and act to both sterically hinder G-protein coupling as well as initiate the process of receptor internalization through clathrin-mediated endocytosis. Because only the liganded receptor is desensitized by this mechanism, it is called homologous desensitization
 * 2) the affinity for β-arrestin may be increased in a ligand occupation and GRK-independent manner through phosphorylation of different ser/thr sites (but also of IL-3 and the C-terminal tail) by PKC and PKA. These phosphorylations are often sufficient to impair G-protein coupling on their own as well.
 * 3) PKC/PKA may, instead, phosphorylate GRKs, which can also lead to GPCR phosphorylation and β-arrestin binding in an occupation-independent manner. These latter two mechanisms allow for desensitization of one GPCR due to the activities of others, or heterologous desensitization. GRKs may also have GAP domains and so may contribute to inactivation through non-kinase mechanisms as well. A combination of these mechanisms may also occur.

Once β-arrestin is bound to a GPCR, it undergoes a conformational change allowing it to serve as a scaffolding protein for an adaptor complex termed AP-2, which in turn recruits another protein called clathrin. If enough receptors in the local area recruit clathrin in this manner, they aggregate and the membrane buds inwardly as a result of interactions between the molecules of clathrin, in a process called opsonization. Once the pit has been pinched off the plasma membrane due to the actions of two other proteins called amphiphysin and dynamin, it is now an endocytic vesicle. At this point, the adapter molecules and clathrin have dissociated, and the receptor is either trafficked back to the plasma membrane or targeted to lysosomes for degradation.

At any point in this process, the β-arrestins may also recruit other proteins—such as the non-receptor tyrosine kinase (nRTK), c-SRC—which may activate ERK1/2, or other mitogen-activated protein kinase (MAPK) signaling through, for example, phosphorylation of the small GTPase, Ras, or recruit the proteins of the ERK cascade directly (i.e., Raf-1, MEK, ERK-1/2) at which point signaling is initiated due to their close proximity to one another. Another target of c-SRC are the dynamin molecules involved in endocytosis. Dynamins polymerize around the neck of an incoming vesicle, and their phosphorylation by c-SRC provides the energy necessary for the conformational change allowing the final "pinching off" from the membrane.

GPCR cellular regulation
Receptor desensitization is mediated through a combination phosphorylation, β-arr binding, and endocytosis as described above. Downregulation occurs when endocytosed receptor is embedded in an endosome that is trafficked to merge with an organelle called a lysosome. Because lysosomal membranes are rich in proton pumps, their interiors have low pH (≈4.8 vs. the pH≈7.2 cytosol), which acts to denature the GPCRs. In addition, lysosomes contain many degradative enzymes, including proteases, which can function only at such low pH, and so the peptide bonds joining the residues of the GPCR together may be cleaved. Whether or not a given receptor is trafficked to a lysosome, detained in endosomes, or trafficked back to the plasma membrane depends on a variety of factors, including receptor type and magnitude of the signal. GPCR regulation is additionally mediated by gene transcription factors. These factors can increase or decrease gene transcription and thus increase or decrease the generation of new receptors (up- or down-regulation) that travel to the cell membrane.

Receptor oligomerization
G-protein-coupled receptor oligomerisation is a widespread phenomenon. One of the best-studied examples is the metabotropic GABAB receptor. This so-called constitutive receptor is formed by heterodimerization of GABABR1 and GABABR2 subunits. Expression of the GABABR1 without the GABABR2 in heterologous systems leads to retention of the subunit in the endoplasmic reticulum. Expression of the GABABR2 subunit alone, meanwhile, leads to surface expression of the subunit, although with no functional activity (i.e., the receptor does not bind agonist and cannot initiate a response following exposure to agonist). Expression of the two subunits together leads to plasma membrane expression of functional receptor. It has been shown that GABABR2 binding to GABABR1 causes masking of a retention signal of functional receptors.

Origin and diversification of the superfamily
Signal transduction mediated by the superfamily of GPCRs dates back to the origin of multicellularity. Mammalian-like GPCRs are found in fungi, and have been classified according to the GRAFS classification system based on GPCR fingerprints. Identification of the superfamily members across the eukaryotic domain, and comparison of the family-specific motifs, have shown that the superfamily of GPCRs have a common origin. Characteristic motifs indicate that three of the five GRAFS families, Rhodopsin, Adhesion, and Frizzled, evolved from the Dictyostelium discoideum cAMP receptors before the split of opisthokonts. Later, the Secretin family evolved from the Adhesion GPCR receptor family before the split of nematodes. Insect GPCRs appear to be in their own group and Taste2 is identified as descending from Rhodopsin. Note that the Secretin/Adhesion split is based on presumed function rather than signature, as the classical Class B (7tm_2, ) is used to identify both in the studies.

title: G protein-coupled receptor


text:
GTPase

GTPases are a large family of hydrolase enzymes that bind to the nucleotide guanosine triphosphate (GTP) and hydrolyze it to guanosine diphosphate (GDP). The GTP binding and hydrolysis takes place in the highly conserved P-loop "G domain", a protein domain common to many GTPases.

Functions
GTPases function as molecular switches or timers in many fundamental cellular processes.

Examples of these roles include:
 * Signal transduction in response to activation of cell surface receptors, including transmembrane receptors such as those mediating taste, smell and vision.
 * Protein biosynthesis (a.k.a. translation) at the ribosome.
 * Regulation of cell differentiation, proliferation, division and movement.
 * Translocation of proteins through membranes.
 * Transport of vesicles within the cell, and vesicle-mediated secretion and uptake, through GTPase control of vesicle coat assembly.

GTPases are active when bound to GTP and inactive when bound to GDP. In the generalized receptor-transducer-effector signaling model of Martin Rodbell, signaling GTPases act as transducers to regulate the activity of effector proteins. This inactive-active switch is due to conformational changes in the protein distinguishing these two forms, particularly of the "switch" regions that in the active state are able to make protein-protein contacts with partner proteins that alter the function of these effectors.

Mechanism
Hydrolysis of GTP bound to an (active) G domain-GTPase leads to deactivation of the signaling/timer function of the enzyme. The hydrolysis of the third (γ) phosphate of GTP to create guanosine diphosphate (GDP) and Pi, inorganic phosphate, occurs by the SN2 mechanism (see nucleophilic substitution) via a pentacoordinate transition state and is dependent on the presence of a magnesium ion Mg2+.

GTPase activity serves as the shutoff mechanism for the signaling roles of GTPases by returning the active, GTP-bound protein to the inactive, GDP-bound state. Most "GTPases" have functional GTPase activity, allowing them to remain active (that is, bound to GTP) only for a short time before deactivating themselves by converting bound GTP to bound GDP. However, many GTPases also use accessory proteins named GTPase-activating proteins or GAPs to accelerate their GTPase activity. This further limits the active lifetime of signaling GTPases. Some GTPases have little to no intrinsic GTPase activity, and are entirely dependent on GAP proteins for deactivation (such as the ADP-ribosylation factor or ARF family of small GTP-binding proteins that are involved in vesicle-mediated transport within cells).

To become activated, GTPases must bind to GTP. Since mechanisms to convert bound GDP directly into GTP are unknown, the inactive GTPases are induced to release bound GDP by the action of distinct regulatory proteins called guanine nucleotide exchange factors or GEFs. The nucleotide-free GTPase protein quickly rebinds GTP, which is in far excess in healthy cells over GDP, allowing the GTPase to enter the active conformation state and promote its effects on the cell. For many GTPases, activation of GEFs is the primary control mechanism in the stimulation of the GTPase signaling functions, although GAPs also play an important role. For heterotrimeric G proteins and many small GTP-binding proteins, GEF activity is stimulated by cell surface receptors in response to signals outside the cell (for heterotrimeric G proteins, the G protein-coupled receptors are themselves GEFs, while for receptor-activated small GTPases their GEFs are distinct from cell surface receptors).

Some GTPases also bind to accessory proteins called guanine nucleotide dissociation inhibitors or GDIs that stabilize the inactive, GDP-bound state.

The amount of active GTPase can be changed in several ways:
 * 1) Acceleration of GDP dissociation by GEFs speeds up the accumulation of active GTPase.
 * 2) Inhibition of GDP dissociation by guanine nucleotide dissociation inhibitors (GDIs) slows down accumulation of active GTPase.
 * 3) Acceleration of GTP hydrolysis by GAPs reduces the amount of active GTPase.
 * 4) Artificial GTP analogues like GTP-γ-S, β,γ-methylene-GTP, and β,γ-imino-GTP that cannot be hydrolyzed can lock the GTPase in its active state.
 * 5) Mutations (such as those that reduce the intrinsic GTP hydrolysis rate) can lock the GTPase in the active state, and such mutations in the small GTPase Ras are particularly common in some forms of cancer.

G domain GTPases
In most GTPases, the specificity for the base guanine versus other nucleotides is imparted by the base-recognition motif, which has the consensus sequence [N/T]KXD. The following classification is based on shared features; some examples have mutations in the base-recognition motif that shift their substrate specificity, most commonly to ATP.

TRAFAC class
The TRAFAC class of G domain proteins is named after the prototypical member, the translation factor G proteins. They play roles in translation, signal transduction, and cell motility.

Translation factor superfamily
Multiple classical translation factor family GTPases play important roles in initiation, elongation and termination of protein biosynthesis. Sharing a similar mode of ribosome binding due to the β-EI domain following the GTPase, the most well-known members of the family are EF-1A/EF-Tu, EF-2/EF-G, and class 2 release factors. Other members include EF-4 (LepA), BipA (TypA), SelB (bacterial selenocysteinyl-tRNA EF-Tu paralog), Tet (tetracycline resistance by ribosomal protection), and HBS1L (eukaryotic ribosome rescue protein similar to release factors).

The superfamily also includes the Bms1 family from yeast.

Heterotrimeric G proteins
Heterotrimeric G protein complexes are composed of three distinct protein subunits named alpha (α), beta (β) and gamma (γ) subunits. The alpha subunits contain the GTP binding/GTPase domain flanked by long regulatory regions, while the beta and gamma subunits form a stable dimeric complex referred to as the beta-gamma complex. When activated, a heterotrimeric G protein dissociates into activated, GTP-bound alpha subunit and separate beta-gamma subunit, each of which can perform distinct signaling roles. The α and γ subunit are modified by lipid anchors to increase their association with the inner leaflet of the plasma membrane.

Heterotrimeric G proteins act as the transducers of G protein-coupled receptors, coupling receptor activation to downstream signaling effectors and second messengers. In unstimulated cells, heterotrimeric G proteins are assembled as the GDP bound, inactive trimer (Gα-GDP-Gβγ complex). Upon receptor activation, the activated receptor intracellular domain acts as GEF to release GDP from the G protein complex and to promote binding of GTP in its place. The GTP-bound complex undergoes an activating conformation shift that dissociates it from the receptor and also breaks the complex into its component G protein alpha and beta-gamma subunit components. While these activated G protein subunits are now free to activate their effectors, the active receptor is likewise free to activate additional G proteins – this allows catalytic activation and amplification where one receptor may activate many G proteins.

G protein signaling is terminated by hydrolysis of bound GTP to bound GDP. This can occur through the intrinsic GTPase activity of the α subunit, or be accelerated by separate regulatory proteins that act as GTPase-activating proteins (GAPs), such as members of the Regulator of G protein signaling (RGS) family). The speed of the hydrolysis reaction works as an internal clock limiting the length of the signal. Once Gα is returned to being GDP bound, the two parts of the heterotrimer re-associate to the original, inactive state.

The heterotrimeric G proteins can be classified by sequence homology of the α unit and by their functional targets into four families: Gs family, Gi family, Gq family and G12 family. Each of these Gα protein families contains multiple members, such that the mammals have 16 distinct α-subunit genes. The Gβ and Gγ are likewise composed of many members, increasing heterotrimer structural and functional diversity. Among the target molecules of the specific G proteins are the second messenger-generating enzymes adenylyl cyclase and phospholipase C, as well as various ion channels.

Small GTPases
Small GTPases function as monomers and have a molecular weight of about 21 kilodaltons that consists primarily of the GTPase domain. They are also called small or monomeric guanine nucleotide-binding regulatory proteins, small or monomeric GTP-binding proteins, or small or monomeric G-proteins, and because they have significant homology with the first-identified such protein, named Ras, they are also referred to as Ras superfamily GTPases. Small GTPases generally serve as molecular switches and signal transducers for a wide variety of cellular signaling events, often involving membranes, vesicles or cytoskeleton. According to their primary amino acid sequences and biochemical properties, the many Ras superfamily small GTPases are further divided into five subfamilies with distinct functions: Ras, Rho ("Ras-homology"), Rab, Arf and Ran. While many small GTPases are activated by their GEFs in response to intracellular signals emanating from cell surface receptors (particularly growth factor receptors), regulatory GEFs for many other small GTPases are activated in response to intrinsic cell signals, not cell surface (external) signals.

Myosin-kinesin superfamily
This class is defined by loss of two beta-strands and additional N-terminal strands. Both namesakes of this superfamily, myosin and kinesin, have shifted to use ATP.

Large GTPases
See dynamin as a prototype for large monomeric GTPases.

SIMIBI class
Much of the SIMIBI class of GTPases is activated by dimerization. Named after the signal recognition particle (SRP), MinD, and BioD, the class is involved in protein localization, chromosome partitioning, and membrane transport. Several members of this class, including MinD and Get3, has shifted in substrate specificity to become ATPases.

Translocation factors
For a discussion of Translocation factors and the role of GTP, see signal recognition particle (SRP).

Other GTPases
While tubulin and related structural proteins also bind and hydrolyze GTP as part of their function to form intracellular tubules, these proteins utilize a distinct tubulin domain that is unrelated to the G domain used by signaling GTPases.

There are also GTP-hydrolyzing proteins that use a P-loop from a superclass other than the G-domain-containing one. Examples include the NACHT proteins of its own superclass and McrB protein of the AAA+ superclass.

title: GTPase


text:
Talk:Gravity wave

Untitled
The page doesn't say what a gravitational wave is.

 * It does now -- I hope satisfactorily. — Toby 10:24 Nov 11, 2002 (UTC)

In case anybody does know: are gravitational waves supposed to be longitudinal waves or transverse waves? Ellywa 12:52, 24 Sep 2003 (UTC)

 * I got an answer from user:Andre Engels at nl:wikipedia, generally it is thought that these waves are transverse, based on general relativity. Ellywa 07:54, 25 Sep 2003 (UTC)

 * It has been proposed that they are a longitudinal scalar waves by some researchers (which my bet is on, though I'm probably wrong ... so everyone will have to wait for further data). It is really unknown [and may exhibit feature of both (i.e., Duality)]. JDR

Infragravity waves
Can someone help provide a definition for Infragravity waves? They are referenced in the article but it is confusing because they are never explained. —Preceding unsigned comment added by AmRadioHed (talk • contribs) 19:45, 19 March 2008 (UTC)

Gravitational waves do not change the strength of gravity.
The concept of "the strength of gravity will go up and down as a gravitational wave passes" is, at least for the case of small amplitudes, wrong.

A GW changes the distance between freely falling test particles, but it will not change the strength of gravity as such. Given a GW with sufficient amplitude passing by while you are standing on a bathroom scale, the reading on the scale would not change. Your legs might be shortened (or lengthened, depending on the phase of the wave), though.

gravity waves are waves generated from centifiqual force due to revolving around the sun,

Grammar and punctuation errors at the beginning of this article make it impossible to understand, even when the punctuation and subject/verb agreement is corrected:

In fluid dynamics, gravity waves are waves generated in a fluid medium (or at the interface between two mediums, e.g., the atmosphere or ocean) which has the restoring force of gravity or buoyancy.

"...which has the restoring force of gravity or buoyancy": Does that refer to the waves, or to the medium? ...and, in either case, what is meant by "the restoring force"?

The article should also explain why this phenomenon should be called a gravity wave when this term means something different when speaking of General Relativity. rowley 23:50, 28 December 2006 (UTC)

It clearly refers to the fluid medium, which is singular. If it was referring to the waves (plural) it would say "which HAVE". Also there is an article about "Gravitaional Waves", the term you are referring to in physics, and that article redirects you here along with explaining how gravitational waves are sometimes INCORRECTLY called gravity waves.70.125.103.247 01:26, 4 February 2007 (UTC)

Frankly I'm annoyed this page exists in it's current phrasing of 'gravity wave' rather than 'wave caused by gravity.' This wording causes too much confusion between it and 'gravitational waves.' —Preceding unsigned comment added by 98.144.5.92 (talk) 01:11, 5 April 2009 (UTC)

Weather
does a gravity wave in a cloud formation indicate anything regarding the intensity of an oncoming storm front or is it simply a phenomena in and of itself? I ask because i witnessed some clouds coming south off of Lake Superior in Upper Michigan (United States) and they preceded a very strong thunderstorm.

Undular Bore Waves
Should the article mention Undular bore Waves? This what I've always heard these called, even by NASA.

Edit: forgot to sign! Chaosratt (talk) 13:21, 13 May 2008 (UTC)

period question
The article says,
 * Gravity waves have a period of between 1 and 30 seconds (1 Hz to 0.033 Hz). Alternatively, infragravity waves generally have a period between 30 seconds to 5 minutes (0.05 to 0.005 Hz).

Are these ranges specifically for ocean waves on Earth, or is it a general physical property of gravity waves that their periods fall in that range? In general I find it hard in parts of this article to determine when it's discussing gravity waves as a general physics concept, and when it's specifically discussing that concept's most prominent application to the Earth's oceans. --Delirium (talk) 17:24, 6 October 2008 (UTC)

 * The whole terminology is quite confusing, and unfortunately this is also the case in many articles and textbooks on the subject. All mentioned bounds, if correct at all, are Earth conditions. Some comments:
 * Tsunami's are certainly gravity waves, as well as tides in the ocean (in shallow seas tides are also strongly affected by dissipation). Both have much larger periods. The indicated range seems to point at wind-generated gravity waves.
 * What is meant with period, since wind waves in a sea state are random?
 * For all gravity waves: the lower range limit of 1 second is definitely to high, since this limit is determined by surface tension (see capillary wave). Wave lengths above 0.1 ~ 0.2 m in case of a water-air interface are hardly influenced by surface tension and can be called gravity waves. This corresponds with periods above 0.3 second (taking 0.15 m as the wavelength).
 * The upper bound of the gravity waves seems reasonable for wind-generated waves, perhaps somewhat low. The wind can force the waves to greater height and longer wavelength as long as the phase speed of the waves is less than the wind speed. A 30 s wave corresponds with a phase speed of 45 m/s, which can be exceeded in extreme hurricanes and typhones, see Saffir-Simpson Hurricane Scale.
 * The term "infragravity wave" suggests somehow that these waves are affected less by gravity. The term is mainly used in coastal engineering to point at subharmonic waves due to non-linear interactions of the Fourier components in the wind waves. But these "infragravity waves" are just as subject to gravity as all other waves. Only in case they are bound/locked/coupled directly by non-linearity to components of the wind waves, these wave components move at a different speed as for gravity waves of the same frequency (but note they are in fact just a part of the gravity waves, only emerging by looking from a "Fourier transform" viewpoint at them). However, the term is also used for the gravity waves emanating in the same frequency band.
 * The given range of 30 s to 5 minutes for the "infragravity waves" seems arbitrary. Short wind-waves of 1 second may also be accompanied by subharmonics at, say 3 s.
 * The further statement in the text: "Infragravity waves can be felt rather than seen as they have a much greater wave energy." is pure nonsense, since the infragravity waves always have less energy than the wind waves they are non-linearly bound to. So I remove that.
 * The above comments are not NPOV (with respect to "infragravity waves") and not accompanied with references.
 * So I think you have a good point and there is quite some work to do here! -- Crowsnest (talk) 18:56, 6 October 2008 (UTC)

Ocean wave image.

The image of the ocean wave (see right) is lovely, and it matches what we normally think of as a wave; but if I'm understanding the article right, it seems like it's a bit misleading, because a "gravity wave" would be out in the middle of the ocean, oscillating periodically, rather than breaking on shore. (I mean, the breaking wave is still a wave, and not wrong per se, but just a bit misleading.) What do y'all think? Should we change to an image of non-breaking ocean waves?

—Ruakh TALK 17:14, 15 April 2009 (UTC)

 * It is a form of a surface gravity wave, whether it is breaking or not, in the ocean or in a lake. Surface gravity wave is in fact the wide class of waves on a gas-liquid interface forced by gravity (and surface tension effects negligible). For me, this picture is fine and not misleading in itself. The caption could be better: "breaking surface gravity wave on an ocean beach" for instance. -- Crowsnest (talk) 17:36, 15 April 2009 (UTC)

Commons categories
Have I understood the distinction between Gravity wave and Gravitational wave correctly in my assigning of media to the Commons categories Commons:Category:Gravity waves and Commons:Category:Gravitational waves? Specifically, Gravity wave talks about hydrodynamic waves and fluids and I am unsure whether that also applies to the particle ripples seen in the rings of Saturn. I am also asking this at Talk:Gravitational wave. 84user (talk) 12:51, 1 May 2009 (UTC)

Gravity Waves in Space
I remember reading this was being studied by physicists. They were looking for (trying to prove or disprove) the existence of gravity waves traveling through space from distant events. Is this the same thing?

75.166.179.110 (talk) 20:16, 16 April 2010 (UTC)

 * No, those are described in: gravitational waves. -- Crowsnest (talk) 21:01, 16 April 2010 (UTC)

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Deep water waves; Hamiltonain formalism
There do not seem to be any existing articles on deep water waves? (currently a red-link). Airy wave theory is about linearized deep-water waves (but in general KdV is non-linear). Stokes wave is about periodic waves (but in general, waves are not periodic). Waves and shallow water is a stub.

From what I can tell, the foundational paper that provides a Hamiltonian formalism for deep water waves is this: The perturbation theory for this is first worked out here: A nice review of the work is here: I'm trying to slap together Draft:Resonant interaction and am trying to figure out what WP articles already exist on these topics. Apparently, the primary wave in which waves interact in deep water is a four-wave resonant interaction. There is a wicked-cool experimental paper on this here: Any help with Draft:Resonant interaction appreciated. 67.198.37.16 (talk) 19:38, 15 September 2020 (UTC)
 * Zakharov, V. 1968 Stability of periodic waves of finite amplitude on a surface of a deep fluid. J. Appl. Mech. Tech. Phys. 2, 190–198.
 * Krasitskii, V. P. 1994 On reduced equations in the hamiltonian theory of weakly nonlinear surface waves. J. Fluid Mech. 272, 1 – 20.
 * Janssen, P. A. E. M. 2009 On some consequences of the canonical transformation in the hamiltonian theory of water waves. J. Fluid Mech. 637, 1–44.
 * F. Bonnefoy, F. Haudin, G. Michel, B. Semin, T. Humbert, S. Aumaˆıtre, M. Berhanu, and E. Falcon, (2018) Observation of resonant interactions among surface gravity waves] J. Fluid Mech.

Unsourced, seemingly contradictory claims (frequency times period should be 2π).
I added a "citation needed" template to the contradictory claim that: "Wind-generated gravity waves on the free surface of the Earth's ponds, lakes, seas and oceans have a period of between 0.3 and 30 seconds (corresponding to frequencies between approximately 3 Hz and 33.3 mHz)". AFAIK, the product of the period and the frequency should be 2π so the numbers in that statement are inconsistent.

Presumably one of the two ranges is correct and the simplest fix would be to delete the other (unsourced) one. Regretfully I have not been able to find a reliable source that is not a circular references to this article so I can not determine which range is correct.

The phrase "wind generated" surface waves does seem to refer to a specific range of frequencies in the sense that frequencies outside that range are unlikely to be generated by wind. Annette Maon (talk) 11:21, 8 December 2022 (UTC)

 * It looks OK to me. See Frequency. Dondervogel 2 (talk) 11:41, 8 December 2022 (UTC)

 * Yes, it is fine. The frequency of a phenomenon times its period is 1.  Angular frequency times period is 2π.  —Quondum 13:41, 8 December 2022 (UTC)

title: Talk:Gravity wave