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Cookbook:Chapati

| Pakistani Cuisine | Indian Cuisine | Flatbread | African cuisines | Vegan Cuisine

The chapati, also known as a roti, is the staple flat bread of Northern India and Pakistan. It can be made from many types of grain, but is most commonly made with finely-ground whole wheat flour. Sometimes it is cooked in a little oil.

Ingredients

 * 3 cups whole wheat flour
 * Salt to taste (about 1 teaspoon)
 * Warm water as required (about 1 ½ cups)
 * Ghee (clarified butter; optional)

Procedure

 * 1) Knead together the flour and water, starting with only a slight dribble of water and adding more as you go until the dough becomes smooth but not too sticky.
 * 2) Cover dough, and let rest for at least 5 minutes.
 * 3) Divide dough into balls and roll out into disks, slightly thicker than denim material; sprinkle with flour as you roll.
 * 4) Place a non-oiled pan over moderately high heat and test its surface temperature by holding your hand over it.
 * 5) When very hot, put a chapati on the pan and press it flat with a spatula or dry cloth to make it rise up.
 * 6) Flip and repeat so it becomes lightly browned on both sides.
 * 7) If desired, brush with ghee.

Notes, tips, and variations

 * Regional variations abound in the detail of preparing and cooking roti. In most Indian cooking, for example, the roti is finished by toasting it in the open flame of the cooker. The aim of this process is to encourage the roti to puff up. The hot air which builds inside because the water inside the roti begins to turn into steam and cooks the roti inside out. This may also be achieved under a grill, or by using a microwave (try 30 seconds on high power). Universally, however, the aim in rolling is to get the roti to a perfectly round shape (for aesthetics) and to create uniform thickness, which is vital for successful cooking.
 * There are Caribbean-specific variations of roti, one of which uses boiled and ground yellow split peas in its preparation.
 * Chapatis are usually eaten with cooked dal (lentil soup) or vegetable dishes like Indian curry. Pieces of the chapati are used to wrap and lift bites of the other dishes.

title: Cookbook:Chapati


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Cookbook:Tadka Dhal (Spiced Lentil Curry) II

| Indian Cuisine | Vegan

Tadka dhal is an everyday staple across South India.

Dhal

 * ½ cup moong dhal, washed
 * 2 cups water

Seasoning

 * 2–3 tablespoon cooking oil
 * 3–4 tablespoon finely diced onion
 * 2 cloves garlic, chopped
 * 1 small sliver of ginger, chopped, or ¼ teaspoon ginger paste
 * 4–5 curry leaves
 * ¼ teaspoon mustard seed
 * ¼ teaspoon cumin seed
 * ¼ teaspoon fenugreek seed
 * ¼ teaspoon of asafoetida (optional)
 * 1–2 tomatoes, cut into eighths
 * 1–2 green chillies, slit lengthwise
 * ¼ teaspoon turmeric powder
 * ¼ teaspoon red chilli (hot pepper) powder
 * 1 pinch of salt (to taste)

Procedure

 * 1) Set the dhal and water in an open pot on moderate heat until quite mushy, adding water if it becomes dry and stirring occasionally. This may take 30 minutes to an hour. A pressure cooker may be used to speed up this part of the process; this should take about 10–12 minutes at 5 psi.
 * 2) Heat the oil in a pan. Add mustard seed, standing well back (they tend to spatter).
 * 3) Add cumin seed, fenugreek, curry leaves, green chillies and onions
 * 4) Wait for the onions to turn translucent. Add garlic and ginger, turn the heat low until the garlic changes to a darker shade. Avoid caramelizing the garlic. Add turmeric, red chilli and asafoetida powder.
 * 5) Throw in tomatoes, and wait for 2–3 minutes, letting the tomatoes fry in the hot oil. This lets the tomatoes pick up the flavors from the spices and also lets the oil-spice (tadka) mixture cool down, stopping the hot frying process that has chilli powder in it. Pour in the mushy dhal, addding salt to taste.
 * 6) Simmer until the tomatoes become soft (5–10 minutes), stirring occasionally.
 * 7) Serve with rice or chapatis.

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


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Cookbook:Masala Chai I

| Indian Cuisine | Beverages

Masala chai is a spiced version of the typical Indian milk tea. As with much of Indian cuisine, the exact mix of dry spices varies greatly and is often handed down in families from one generation to the next.

Masala mixture

 * 100 grams powdered ginger
 * 25 grams cloves
 * 100 grams whole black peppercorns
 * 60 grams whole cinnamon, broken small, or 40 grams ground cinnamon
 * ½ seed of nutmeg, crushed
 * 35 grams green cardamom pods

Chai

 * ½ cup water
 * 1 ½ teaspoon sugar
 * ¾ teaspoon dried tea leaves—to be traditional, a strong Indian tea such as an Assam is best.
 * 1 pinch of masala mixture
 * ½ cup milk

Masala

 * 1) Combine all of the spices, and blend well in an electric grinder.
 * 2) Store the powder in a clean container at room temperature; you only need a small quantity for each cup of chai, and a full recipe will keep you stocked full of chai for months.

Chai

 * 1) Boil water and milk together in a saucepan.
 * 2) Add sugar, tea leaves, and masala. Boil until the mixture becomes dark (about 5–10 minutes); the longer you boil, the stronger the chai.
 * 3) Strain into teacups to serve.

Notes, tips, and variations

 * Let the remaining solids cool and sprinkle them on your plants for an excellent fertiliser.
 * Tea masala or garam masala from a store can be used to get around the masala mixture process; however, pre-ground spices lose their flavor over time.
 * When making the chai, boil the water and milk separately, and in step two add the tea leaves and masala to the boiling water, boiling until the tea is as strong as you like. Only then add the milk to the mix. This can speed up the process without affecting the flavor. This method is often used by restaurants to serve chai in large quantities quickly as orders are taken.
 * Optionally turn off the heat in the end, cover, and let sit for about 5 minutes for a richer flavor.
 * Try adjusting the ratio of milk to water. For a richer milky tea, try two parts milk to one part water.
 * Leave out the sugar for a more adult flavor. Sugar can be added while drinking if so desired.
 * Try other combinations of South Asian spices. Each region in which chai is commonly available has its own popular or traditional spice mix. One optional addition to masala chai is fennel seeds.
 * Add a piece of a lemongrass leaf (called lili cha in Gujarati), while the water is still boiling (before adding milk). This gives a nice flavor to the tea. Mint, fresh ginger, and/or holy basil (tulsi) can also be added.
 * To make ground ginger: Select good quality ginger and wash to remove soils and other foreign objects. Cut into thin slices. Spread evenly in trays. Dry under the sun or in oven under moderate heat or (70ºC). Pulverize using blender or grinder. Pack and seal tightly.

fa:کتاب آشپزی/چای مصالح

title: Cookbook:Masala Chai I


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Cookbook:Baingan Bartha (South Indian Eggplant with Coconut and Chili) I

| Indian Cuisine | Vegetarian

Baingan bartha is an eggplant (aubergine) dish much loved all over India. This southern version of the dish is very different from northern varieties, and well suited to the cuisine of the region.

Ingredients

 * 1 ea. (1 pound / 450 kg) eggplant (aubergine)
 * 2–6 green chillies, as desired
 * 1 cup fresh ground coconut
 * 1 cup chopped fresh coriander leaves (cilantro)
 * 2 cups paneer or yoghurt (optional)
 * Salt to taste

Procedure

 * 1) Roast the eggplant directly over a low flame. Don't be afraid to set it right on the gas burner, turning it regularly until the skin becomes blackened and brittle and the flesh soft (about 15–20 minutes).
 * 2) Set aside to cool.
 * 3) Grind the chillies, coconut, and coriander together in a food processor to form a paste.
 * 4) Peel the eggplant skin off and mash the flesh to a uniform pulp by hand.
 * 5) Mix in the coconut paste and paneer/yogurt, along with salt to taste.
 * 6) Serve with chapatis, dosa or rice.

Notes, tips, and variations

 * Baingan bartha is commonly produced with coriander (seeds) and/or cilantro (leaves, from the same plant, and thus sometimes confusingly called coriander as well).


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Cookbook:Upeseru (Indian Lentils with Greens)

| Indian Cuisine | Vegan Cuisine

Upeseru is a rural speciality of the South of India, and villages around the state of Karnataka in particular. The main recipe is for a solid dish of lentils and greens, and the water drained from this is often used in an accompanying wet sauce to be eaten with mudde (ragi balls). The combination of the three is a common complete meal.

Solids

 * 1½ cups dhal or other lentils, cooked but not drained
 * 5 handfuls of a leafy green such as spinach, chopped
 * 2 teaspoons oil
 * 1 teaspoon mustard seed
 * 10 curry leaves
 * 1 medium onion, diced
 * 1–6 green chillies, split lengthwise, according to taste
 * Salt to taste

Broth

 * 1–6 green chillies, to taste
 * ½ teaspoon fresh tamarind per chilli used
 * 1 handful of coriander
 * 8 cloves garlic
 * 2 teaspoons whole black peppercorn
 * 2 teaspoons cumin
 * Spinach-lentil water
 * ½ lemon

Solids

 * 1) Fry the mustard seed, curry leaves, onion and green chillies in oil until the onions are partly browned.
 * 2) Meanwhile, set the lentils on the stove. Add the chopped spinach and boil until the spinach is tender.
 * 3) Drain and set the water aside separately for the next part.
 * 4) Stir in the spice mixture and salt to taste, keeping on the heat until the flavours have blended.

Broth

 * 1) Dry-roast the chillies and tamarind slightly, if desired.
 * 2) Grind all dry ingredients together with a little water to make a chutney.
 * 3) Bring the spinach broth to a boil and let simmer for 2 minutes.
 * 4) When serving, mix in a spoonful of the chutney and squeeze in lemon juice.
 * 5) Eat with mudde (ragi balls).


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Cookbook:South Indian Millet Swallow (Mudde)

| Indian recipes

Mudde is a compact ball swallow made from finger millet. It is a lunchtime staple of rural communities in Karnataka, Tamil Nadu and Andhra Pradesh in South India, and an important source of long-lasting energy among the rural poor.

Serving immediately is preferable, but the balls can also be packed and eaten cold later. Before eating, if desired, poke a hole in the ball with your finger and pour in a little ghee. Dip pieces of the ragi dough in a watery sauce like upeseru broth and swallow; do not attempt to chew. Eat along with the solid upeseru for a complete meal that will keep you going all day.

Ingredients

 * 2 ½ cups ragi (finger millet) flour
 * 5 cups water
 * Ghee

Procedure

 * 1) Boil the water in a pot, add a little of the flour to make a paste, then add the rest of the flour.
 * 2) Stir once with the handle of a wooden spoon and leave it in the pot.
 * 3) Keep on low heat for about 10 minutes until it smells cooked.
 * 4) Stir until the mixture turns dark reddish-brown. Once it begins to leave the sides of the pot, remove the pot from the fire and stir vigorously for 5–10 minutes—it's hard work, but the longer you keep at it, the lighter it will be.
 * 5) Pull the mixture out and form into balls of about fist size.


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Cookbook:Appam (Fermented Rice Pancake)

| Indian Cuisine | Sri Lankan Cuisine

Appam, a fermented rice pancake, is a speciality of the South Indian coastal state of Kerala. It is especially popular among the Christian communities of that state. Appam are often served along with a coconut-flavoured vegetable stew. It is also very popular in Sri Lanka, where it is known as "appa" (or "hopper") and often served with an added egg.

Ingredients

 * 1½ cups uncooked white rice
 * 1½ cups fresh grated coconut
 * 1 tablespoon sugar
 * 1 teaspoon salt, or to taste
 * 2 tablespoons white rice, cooked
 * water for soaking rice, and 2 to 2½ cups for grinding
 * ½ teaspoon yeast or kefir, to start the ferment (optional)

Procedure

 * 1) Soak the raw rice in water.
 * 2) Grind the soaked rice until about ¼ ground.
 * 3) Add the grated coconut along with a little water and continue grinding.
 * 4) Add the sugar, cooked rice and yeast or kefir, and keep grinding until the whole mixture becomes smooth. It should be thinner than pancake batter.
 * 5) Transfer it to a wide open container and leave it to rise overnight.
 * 6) The next morning, add salt and refrigerate the batter until use.
 * 7) To fry the appams, use a tava or a small bowl-shaped pan with either a non-stick coating or a little oil (coconut or any other refined oil) or ghee.
 * 8) Pour a full serving spoon of batter into the middle of the pan and swirl it around a single time so that a little of the batter sticks to the sides.
 * 9) Cover the pan with a hot lid and remove the appam with a spatula after 2–3 minutes, when it becomes slightly browned around the edges. It should be round, with a thick centre and thin, lacy edges.

Notes, tips, and variations

 * The batter should ferment overnight without any added starter, but often won't. Yeast (or better still, kefir) can be added to help it ferment.
 * The grinding can be done in a blender. Make sure that there is enough liquid so that it all swirls around in the blender, mixing properly.

title: Cookbook:Appam (Fermented Rice Pancake)


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User:Nixda~enwikibooks

Hello, my name is Stephan and I am from bavaria/germany.

This are some of my web projects:
 * Team 2 Hörnchen
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 * Abnehmen mit Absolut Gesund
 * Socio Medico
 * Nahrungsergänzung - Österreich
 * Designerschmuck Uhren
 * Shop-System aus Mainburg
 * Nutrishop Mainburg Sporternährung
 * Wein

title: User:Nixda~enwikibooks


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Cookbook:Keralan Vegetable Stew

| Indian Cuisine | Vegan

This coconut-flavoured vegetable stew is a famous dish of the South Indian coastal state of Kerala. It is often served with appam (rice pancakes). Though frequently made with chicken, this recipe is for the purely vegetable version of the stew.

Ingredients

 * ½ coconut, freshly grated
 * 1½ cups boiled vegetables (carrots, green beans, potatoes, peas, etc.)
 * 2 Tbsp oil
 * 1 onion, diced
 * 1 very small piece of ginger, chopped
 * 2–5 green chillies (as desired), split lengthwise
 * 10 curry leaves
 * 4 cloves
 * 2 small pieces cinnamon
 * 2 pods green cardamom
 * 1 Tbsp vinegar
 * 1 Tbsp flour or rice flour or cornstarch
 * 1 pinch of salt
 * 1 tsp ground black pepper
 * 1 tsp mustard seed
 * 1 shallot

Procedure

 * 1) Pour ¾ cup of water into the grated coconut. Squeeze out the milk through a strainer. Set aside; this is first milk.
 * 2) Pour ½ cup of water into the same coconut and squeeze out the second milk. Keep this aside as well.
 * 3) In a large pan, heat oil and add the cloves, cinnamon, and cardamom.
 * 4) Add the chopped onion, ginger, chillies and curry leaves. Fry until the onion is slightly browned.
 * 5) Add the boiled vegetables and stir for 1 minute.
 * 6) Pour in the second milk and boil for about 5–7 minutes.
 * 7) Add salt. Dissolve the maida/rice flour in a little water and add it to the sauce.
 * 8) When it boils again, add the first milk.
 * 9) Remove from the flame when it starts to boil once more.
 * 10) Season with the pepper, mustard, and shallot.

Notes, tips, and variations

 * You can use cornflour instead of rice/maida flour to thicken the sauce.

title: Cookbook:Keralan Vegetable Stew


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Cookbook:Basic Indian Tomato Gravy

| India | Vegan Cuisine

This traditional Indian tomato gravy can be used as a base for all sorts of vegetables, boiled eggs, cubed paneer or chicken. This is often referred to as a "curry". It is usually eaten with plain white rice or rice mixtures.

Ingredients

 * 5 tomatoes, diced large
 * 1 onion, diced small
 * 1 tablespoon ghee
 * ½ teaspoon ginger paste
 * 5 cloves garlic, pounded
 * 1 teaspoon chile powder
 * ½ teaspoon coriander powder
 * ½ teaspoon cumin powder
 * ¼ teaspoon turmeric powder
 * Salt to taste

Procedure

 * 1) Fry the onions in hot ghee until they start to brown.
 * 2) Add the ginger and garlic and stir, then add the powdered spices. Blend well.
 * 3) Throw in the tomatoes and salt to taste.
 * 4) Turn the flame down to medium and cover for ten minutes. This will form a spicy gravy to which you can add any mixture of vegetables or boiled eggs or fried fish or chicken or lamb/goat.

Notes, tips, and variations

 * If adding cooked vegetables, keep the pot on the flame until they are uniformly heated; for uncooked vegetables, cook as long as necessary.
 * With chicken/lamb/goat, add the marinated poultry/meat after frying the ginger garlic paste and adding the dry spice powders. Sear the poultry/meat on high heat, turning the pieces continuously for about 10–15 minutes until the juices get sealed inside. Add the tomatoes after this step. Continue cooking as per above recipe. Alternatively, you have the option of frying /roasting/grilling the marinated poultry/meat separately, before adding to the curry, then letting it simmer for at least 20 minutes.
 * You can add a little cayenne and cumin and leave out the chili powder (though "chili powder" in Indian recipes is cayenne/powdered chilis)
 * Depending on the freshness of your spices, you may want to add extra spices in the same ratio to achieve a stronger flavour.
 * Generally, in Indian cuisine, for lamb or goat (known locally as 'mutton'), you can use all the above ingredients to make the gravy (curry). Some recipes use curd/yogurt, while some use tomatoes for the balancing tart flavour. With chicken, lamb and goat, marination is preferred. Also, various spice powders and spices (sabut garam masala) are added depending on the recipe. For example, cloves and cinnamon can be added to the hot oil, to give an excellent flavour.
 * For a vegan version of this recipe, substitute the ghee with coconut oil or other vegetable oil.
 * You can also use a pressure cooker instead of the stovetop; in this case, cook it for 6−7 whistles on a medium flame. This is especially useful when cooking lamb or goat as the meat is tougher than chicken.
 * You can also use fried onions as garnish to get a gravy with a different flavor. This is used frequently in chicken recipes.

title: Cookbook:Basic Indian Tomato Gravy


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Cookbook:Kashmiri Pulao

| Rice Recipes

This very fancy Kashmiri pulao, or Kashmiri Pallao, is from the Northern Indian state of Kashmir. Although it is a frozen region high in the Himalayas, Kashmir lies along the ancient overland trade routes between India and Central Asia, and the cuisine is famous for using a huge assortment of nuts and dried fruits from all over Central and Western Asia.

Ingredients

 * 3 tablespoons ghee or butter
 * 5 cloves
 * 4 pods green cardamom
 * 1 cinnamon tree leaf (or substitute 2 bay leaves)
 * 1 small onion, sliced thin
 * 1 ½ teaspoons ginger-garlic paste
 * 2 green chillies, split lengthwise
 * 1 pinch of salt
 * 3–4 strands saffron
 * 1 tablespoon milk
 * ½ kilogram basmati or other long-grained rice, cooked and drained
 * 100 grams dried dates, pitted and sliced thin
 * 50 grams white raisins
 * 50 grams cashew nuts
 * 50 grams pistachio nuts
 * 50 grams almonds, blanched and diced

Procedure

 * 1) Heat ghee or butter in a large wide pan or wok.
 * 2) Add the cloves, cardamom, and cinnamon tree leaf.
 * 3) Add the chopped onion, and fry until it just begins to turn brown.
 * 4) Add ginger-garlic paste and chillies and fry for about 1 minute before tossing in all of the dried fruits and nuts.
 * 5) Add salt to taste.
 * 6) Turn the flame down to low.
 * 7) Soak the strands of saffron in milk, mixing until the milk turns orange.
 * 8) Pour the cooked rice into the pan and sprinkle the saffron-milk on top.
 * 9) Stir very carefully so as not to break or mash up the rice grains, mixing the flavourings and saffron colour in uniformly and heating the rice.
 * 10) Mix in dried fruits and nuts.
 * 11) Add more ghee according to your preference.
 * 12) Serve with a gravy such as the basic tomato gravy.

Notes, tips, and variations

 * Try adding paneer fried in ghee to the pulao.

title: Cookbook:Kashmiri Pulao


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Cookbook:Khara Pongal (Rice and Lentil Porridge)

| Rice Recipes

Khara pongal is a savoury porridge-like dish that is traditionally prepared in South India for the Makar Sankranti festival that heralds the arrival of summer. The sweet pongal variety differs only in the spices added, and the two are often cooked together from the same batch of rice and dhal.

Ingredients

 * ½ cup white rice
 * ½ cup moong dhal
 * 3 cups water
 * ½ tablespoon turmeric powder
 * ¼ cup chopped cashew nuts
 * 10 curry leaves
 * 1 tablespoon coarsely-ground black pepper
 * 1 tablespoon cumin seeds
 * 2 green chillies, split lengthwise
 * 1 tablespoon oil
 * 1 tablespoon ghee (or substitute butter)
 * ½ tablespoon mustard seed
 * Salt to taste

Procedure

 * 1) Cook the rice and dhal together with turmeric powder in a pot or pressure cooker until mushy.
 * 2) Heat a little ghee in a large pan and brown the cashew nuts. Remove them from the pan.
 * 3) Add the rest of the ghee and the oil and heat.
 * 4) Throw in all of the spices, starting with the mustard seed and finishing with the cashew nuts.
 * 5) Mix in the rice and dhal, warming through. If it is too thick, add a little water.
 * 6) Add salt and extra ghee to taste. You can also add some grated coconut at the end.


text:
Cookbook:Chakarai Pongal (Sweet Rice and Black Gram Pudding)

| Indian Cuisine | Dessert | Rice

Chakarai pongal is a sweet and buttery porridge-like dish that is traditionally prepared in South India for the Makar Sankranti festival that heralds the arrival of summer. The khara pongal variety differs only in the spices added, and the two are often cooked together from the same batch of rice and dhal.

Ingredients

 * ½ cup white rice
 * ½ cup moong dhal
 * 4 cups water
 * ¼ cup chopped cashew nuts
 * ¼ cup white raisins
 * 1 tablespoon cardamom powder
 * 1 cup ghee (or butter)
 * ¾ cup jaggery
 * ¼ cup milk

Procedure

 * 1) Cook the rice and dhal together with cups of water in a pot or pressure cooker until mushy.
 * 2) Meanwhile, melt the jaggery with 1 cup of water in a pan.
 * 3) Add the cardamom to the jaggery as it melts.
 * 4) Mush the rice and paruppu (dal) mixture well and add to the pan of jaggery.
 * 5) Stir well and cook on low heat till the mixture comes together well.
 * 6) Heat 4 tablespoons of the ghee in a separate pan and fry cashews to golden brown.
 * 7) Add raisins and fry for a few more seconds or until they swell up.
 * 8) Add the nuts and raisins to into the pongal.
 * 9) Serve hot with an additional dollop of neyyi or ghee.


text:
Guitar

The aim of this book is to introduce beginners to the basic concepts of the guitar. Important techniques are given their own sections with exercises and examples provided. It includes an extensive section on amplifiers and numerous tips and advice on all aspects of the guitar. Music theory concepts are clearly presented and explained.

Getting Started

 * /Different Types of Guitars/
 * /Anatomy of a Guitar/
 * /Buying a Guitar/
 * /Buying an Amplifier/
 * /Tuning the Guitar/
 * /Tablature/
 * /Lead Guitar and Rhythm Guitar/

For Beginners

 * /The Basics/
 * /Open Chords/
 * /Intervals and Power Chords/
 * /Muting and Raking/
 * /Learning Songs/
 * /Technical Exercises/

Lead Guitar

 * /Scales/
 * /Scale Theory/
 * /Major Patterns/
 * /Picking and Plucking/
 * /Arpeggios and Sweep Picking/
 * /Slides/
 * /Hammer-ons, Pull-offs, and Trills/
 * /Bending and Vibrato/
 * /Harmonics/
 * /Tremolo Bar Techniques/
 * /Tapping/
 * /Octaves/

Rhythm Guitar

 * /Chord Types/
 * /Barre Chords/
 * /Movable Chords/
 * /Chord Progressions/
 * /Alternate Picking/
 * /Tremolo Picking/
 * /Rhythm/

Playing Styles

 * /Folk Guitar/
 * /Blues/
 * /Slide Guitar/
 * /Rock/Alternative Guitar/
 * /Country and Western/
 * /Metal/
 * /Jazz/
 * /Classical Guitar/
 * /Flamenco/
 * /Reggae/

General Guitar Theory

 * /Tone and Volume/
 * /Singing and Playing/
 * /Writing Songs/
 * /Playing With Others/
 * /Recording Music/
 * /Tuning Your Ear/
 * /Playing What You Hear/

Equipment

 * /Guitar Accessories/
 * /Effects Pedals/
 * /E-bow/
 * /Cables/
 * /Bass Guitar/
 * /Harmonica and Guitar Combo/

Maintenance

 * /Guitar Maintenance and Storage/
 * /Adjusting the Guitar/
 * /Stringing the Guitar/

Appendices

 * /Alternate Tunings/
 * /Scale Manual/
 * /Chord Reference/
 * /Blues Exercises/
 * /Song Library/
 * /Blanks/ - These are templates used for writing tabs and making scales in this book.

About this Book

 * /Authors/

Music Theory Wikibook: The Basics

 * Introduction
 * Music Notation Systems
 * Rhythm
 * Scales and Intervals
 * Modes
 * Chords
 * Chord Structures
 * Consonance and Dissonance

Gitarre Apprendre la guitare Chitarra גיטרה Gitaar Nauka gry na gitarze Guitarra Kitarakirja Guitar 吉他

title: Guitar


text:
Cookbook:Cuisine of China

| East Asian cuisines

Chinese cuisine is not a single entity, but instead is made up of the individual cuisines of many provinces and ethnics groups of China. So combined together, there are perhaps thousands of types all over China. That is why Chinese have a famous old saying "Cuisine is heavenly in first priority" (民以食为天). However, there are some common ingredients and philosophies about most Chinese foods.

First and foremost, Chinese believe that having a knife at the table is barbaric. This means dishes are usually prepared in portions to be eaten directly with chopsticks or spoons. Second, Chinese foods are usually served warm and well-cooked.

Common ingredients include:

 * Beef
 * Chicken
 * Duck
 * Pork
 * Soybeans (tofu, soy sauce)
 * Vegetables

Genres of Cuisine
It is a common sense to most Chinese that there are eight main genres (or types) of cuisine in China. They are:
 * Chuan cuisine（川菜）(Combined with Cheng-Du and Chong-Qing regional cuisines; Spicy and hot)
 * Hui cuisine（徽菜）(Combined with Wan-nan, Yangtze river drainage area; Very good at pot-roasting and using sugar)
 * Lu cuisine（鲁菜）(Combined with Ji-Nan and Jiao-Dong regional cuisines; Garlic and seafood)
 * Min cuisine（闽菜）(Combined with Fuzhou, Quanzhou and Xiamen; South sea seafood)
 * Su cuisine（苏菜）(Combined with Yang-zhou,Suzhou and Nanking; Good at braising and soup;Fresh and yum)
 * Xiang cuisine（湘菜）(Specially hot and heavily using of chilly and vinegar)
 * Yue cuisine（粤菜）(Combined with Guangzhou, Chaozhou and Dongjiang; Simple yet complex, crisp and fresh)
 * Zhe cuisine（浙菜）(Combined with Hangzhou, Ningbo and Shaoxing; Soft and good-smelling)

The genres are mainly based on the provinces of old China.

However, nowadays new cuisine types are created and there could be more than eight types.

Cuisines
The cuisines of modern China:
 * Anhui cuisine
 * Beijing cuisine
 * Chaozhou cuisine
 * Chinese cuisine (Imperial or aristocratic cuisine)
 * Fujian cuisine
 * Guangdong cuisine (Cantonese) - fresh ingredients, very light spices
 * Henan cuisine
 * Huai-Yang cuisine
 * Hubei cuisine
 * Hunan cuisine
 * Jiangsu cuisine
 * Liaoning cuisine
 * Shaanxi cuisine
 * Shandong cuisine
 * Shanghai cuisine
 * Sichuan cuisine (Szechuan) - includes use of spicy peppers
 * Yunnan cuisine
 * Zhejiang cuisine

Others:
 * Hangzhou cuisine
 * Manchurian cuisine
 * Xinjiang cuisine - heavy use of lamb

Recipes
Please see our listing of Chinese recipes.

title: Cookbook:Cuisine of China


text:
Cookbook:Sheer Khurma

| Indian Cuisine | Dessert

Sheer khurma is a sweet noodle soup served by Muslims in Indian and other South Asian countries to guests during the holy month of Ramadan. The recipe originally comes from Mughal-India.

Ingredients

 * 200 g dry vermicelli
 * 1¼ cups ghee
 * 100 g dried dates, soaked overnight, pitted and chopped thin
 * 100 g almonds, blanched and slivered
 * 100 g white raisins
 * 100 g halved cashew nuts
 * 12 cups milk
 * 2 cups cream
 * 4 cups water
 * 3 cups white granulated sugar
 * 2 tbsp cardamom powder

Procedure

 * 1) Heat the ghee in a large pot over a low heat.
 * 2) Add the cashew nuts to the ghee, and fry until browned.
 * 3) Turn off the flame and add the raisins. When the raisins swell up, take both them and the cashews out of the ghee with a spoon and set aside.
 * 4) Switch the low heat back on and heat the ghee. Add the vermicelli and fry, stirring so it turns golden-brown. Watch it carefully so it does not burn.
 * 5) Pour in the milk and water. Add the cashews and raisins back into the mixture.
 * 6) Add the sliced dates and almonds. Cook for about 2 minutes, or until the vermicelli starts to get flexible; then add sugar.
 * 7) Keep on the low flame for another 2 minutes, then add cream and cardamom powder.
 * 8) Heat just a little longer and mix well.
 * 9) Serve hot.

title: Cookbook:Sheer Khurma


text:
Guitar/Anatomy of a Guitar

This chapter presents an overview of the different parts most commonly found on the three main types of guitar.

Overview of Components

Body
The body of a guitar consists of a treble or upper bout (the half of the guitar closest to the neck), the bass or lower bout (the wider half of the guitar), and the waist bout (the narrow section between the treble and bass bouts).

The body is one of the most important factors in shaping the overall tone of a guitar. It provides the resonance that shapes the tonal qualities. It determines the volume of acoustic guitars and affects the sustain of electric guitars.

Resonance is affected by:
 * the types of wood used
 * whether the body is made from layered woods (ply) or single pieces
 * whether the body is hollow or solid
 * the shape and size of the body

The woods listed below are used in the construction of both acoustic and electric guitars.

Tone wood

 * Agathis (also known as Commercial Grade Mahogany or Poor Man's Mahogany) is a tropical pine commonly found throughout south-east Asia. It is a plantation-wood used mainly for building cabinets. Agathis is cheap and usually used in the construction of budget guitars. Its tone is similar to mahogany but more bland sounding with a less complex response.

 * Alder is a lightweight wood that provides a clean balanced tonal response and good resonance. Its soft and tight porous structure is similar to basswood but with a bolder hard grain pattern that adds to the stiffness making it more robust. Alder has a medium light tan color and provides a balanced tone across the frequency range with a slight upper mid-range producing a clean sound. Its resonance provides a good dynamic range.

 * Ash has an open grain pattern which requires a lot of lacquer to seal and this can have a marked affect on the length of the sustain. Ash is typically used in mid-range priced guitars. Ash offers two varieties for guitar construction and they differ in tone:

 * (1) Northern hard ash (also known as Baseball Bat Ash) is hard, heavy and dense. This gives it a bright tone and long sustain.
 * (2) Swamp Ash (also known as Southern Soft Ash) comes from swamps in the Southern USA. Swamp Ash grows underwater which makes the wood lightweight and porous. Many Fender guitars from the 1950s were built with Swamp Ash.  It has hard grain lines between its softer layers and a creamy light tan color with bold darker grain patterns. Its tonal qualities are a balance between brightness, warmth and dynamic range with clear bell-like highs, slightly scooped mids and strong lows. Swamp Ash has good resonance across the whole frequency spectrum and therefore can sound quite complex.
 * (2) Swamp Ash (also known as Southern Soft Ash) comes from swamps in the Southern USA. Swamp Ash grows underwater which makes the wood lightweight and porous. Many Fender guitars from the 1950s were built with Swamp Ash.  It has hard grain lines between its softer layers and a creamy light tan color with bold darker grain patterns. Its tonal qualities are a balance between brightness, warmth and dynamic range with clear bell-like highs, slightly scooped mids and strong lows. Swamp Ash has good resonance across the whole frequency spectrum and therefore can sound quite complex.

 * Basswood is a lightweight (lighter than Alder) close-grained wood with a consistent and tight grain pattern. Its very soft with light colors that range from almost white to medium tan. It requires a hard finish, such as polyester, for protection and good engineering to allow the screws and screw-holes to hold the parts. The installation of a tremolo system on such a softwood also means the body needs to be thicker to prevent cracking. Tonally, basswood has a warm soft tone which attenuates both the high and extreme low frequencies. It also creates a pronounced midrange fundamental frequency response and a reduced smoother high-end response. The tonal response compared with other softwoods such as ash and alder is less complex with a narrower dynamic range. Basswood doesn't excel in clean sounds though when coupled with distortion and overdriven amplifier produces a metal-lead sound much favoured by some rock guitarists. It is used in the construction of budget guitars and expensive guitars.

 * Cedar became popular in the mid-twentieth century after master luthier Jose Ramirez III of Madrid pioneered the use of red cedar as a substitute for the increasingly scarce European spruce. It is now considered one of the world's premier tone woods.

 * Mahogany is a highly dense, heavy wood with a fine, open grain and large pores. The color is reddish brown. Tonally, it provides good low frequencies, a compressed mid-range and smooth sounding highs. Overall, its tone is mellow, soft and warm with a full and thick quality. Its density provides excellent sustain and also makes it less susceptible to dents and scratches. Its density and weight have led some manufacturers to experiment with a thinner body as seen on the Ibanez S series.

 * Nato (also known as Eastern Mahogany) is a native wood from the Caribbean and South America. Nato is not a mahogany though its appearance and tonal similarities to mahogany has led to it being used on guitars as a mahogany substitute. It is also a commercial grade wood used in cabinet building. It has a bright tone with pronounced midrange but lacks in sensitivity and punch compared with mahogany. Nato is used by the manufacturer B.C. Rich for their Assassin range.

 * Maple is used for the backs and sides of more expensive acoustics like the J200 series by Gibson. Though not generally used as a table for flat-topped instruments; it is the wood of choice for arched top guitars, mandolins, and the violin family of instruments. Its usually white in color with tight pores and thin grain lines. There are two main types of American maple:

 * (1) Eastern Hard Maple (also known as Hard Rock Maple or Sugar Maple and usually associated with maple syrup) is an excellent tonewood. As named, it is very hard and dense with a medium weight which makes it difficult to work and therefore it is usually reserved for necks. When used for the body, it provides a bright sound with very strong highs and upper mid-range but quieter bass frequencies. Overall, hard maple has a very long sustain. Eastern hard maple can exhibit a figure (grain pattern) called the bird's eye whose aesthetic appeal has led to it being used for guitar tops and backs usually bookmatched.
 * (2) Western Soft Maple (also known as Big Leaf Maple) is much lighter in weight than Hard Maple. It has a bright tone with good bite and attack though not as brittle as hard maple. Its tonal qualities produce singing highs with a tight low-end. This kind of maple is often seen with a figure called flame or curl and less commonly a figure called quilt.
 * Rosewood is used for the backs and sides of acoustics and also for fingerboards. It possesses an extremely high density which makes for an acoustically reflective tone wood. Its color is dark brown with reddish, purple or orange streaks running through it. There are many varieties of rosewood that are suitable for guitar construction.
 * Rosewood is used for the backs and sides of acoustics and also for fingerboards. It possesses an extremely high density which makes for an acoustically reflective tone wood. Its color is dark brown with reddish, purple or orange streaks running through it. There are many varieties of rosewood that are suitable for guitar construction.
 * Rosewood is used for the backs and sides of acoustics and also for fingerboards. It possesses an extremely high density which makes for an acoustically reflective tone wood. Its color is dark brown with reddish, purple or orange streaks running through it. There are many varieties of rosewood that are suitable for guitar construction.

 * Poplar is a wood used by manufacturers of budget guitars most notably Danelectro who use masonite (top and back) glued to a poplar frame (sides). Its a closed grain wood with a greyish-green color and similar to alder in weight and tone. Due to the resurgence of interest in budget guitars from the 1950s onwards some modern reissues that use poplar are relatively expensive.

 * European Spruce is a premium tonewood used in the design of many stringed instruments including the violin, viola and lute. Increasing scarcity has resulted in the use of substitutes such as the North American species of spruce and red cedar.

 * Walnut is a medium hard wood with a strong grain pattern. Its body has a constant density. Walnut is harder, heavier and more dense than mahogany and therefore closer to maple. Tonally, it is warmer than maple with a solid low-end. The mid-range is relatively complex and the high-end is smooth and bright. Due to its density it provides good sustain.

Body top
Some electric guitars have an extra top added to the body to blend the tonal qualities of different types of wood together. Maple with figuring is a popular top and produces a pronounced look and tone (adds brightness). Body tops are not used on acoustics since the layering of two pieces of wood for the table would inhibit the resonance and dull the tone.

Bridge
The bridge is found on the lower bout of the body and forms one one end of the vibrating length of the strings, the other end being the nut, which is located at the end of the fretboard. On most electric guitars, the height of the bridge is adjustable by screws, allowing the guitars action – distance that the strings sit above the frets – to be raised or lowered. On most electrics, the horizontal position of the bridge saddles is also screw-adjustable, allowing the guitar's intonation to be set by the user. These adjustments are discussed further in the Adjusting the Guitar section.

Depending on the guitar, the strings may terminate at the bridge or just pass over it.

The bridge of an acoustic consists of two parts: a saddle and the tie block. Saddles are either a piece of plastic or polished bone. Acoustic guitar saddles are made with a smooth top edge (no notches) and the base of the saddle is seated in a groove cut into the tie block. The wood tie block of a classical guitar is glued to the lower bout and acts as a string terminator. A classical guitar string is pushed through the hole in the tie block and the string is then brought back under itself three or four times and pulled tight to form a knot. Once the saddle is seated in the groove of the tie block the tension of the strings clamp it.

Steel string acoustics also have a saddle and tie block though due to the strings having terminating end balls there is no need to knot. The ball end of the string is thrust into a vertical hole in the tie block and secured with a pin. The position and height of the saddle and tie block on acoustics are set by the manufacturer, and usually do not require user adjustment. Adjustments to the height of the acoustic saddle are possible by shaving (lowering) the saddle though this job is best left to a luthier since if too much is taken off, a new saddle will required unless one resorts to the temporizing measure of shims.

The design of bridges varies between manufacturers and the above generic descriptions may not apply to some guitars.

Fretboard and Frets
The fretboard is a piece of wood that is glued to the front of the neck. These are commonly made of rosewood though other hard woods such as ebony may also be used. Embedded in the fretboard are a number of metal frets (fret-wire) usually numbering twenty one to twenty-four. Strings are pressed down behind a fret which changes the length that is left free to vibrate thereby producing a different note. A simple demonstration is to be found on the twelfth fret. On all guitars this is the fret that divides the string exactly in half and produces a note an octave higher than the open note. Any open string that maintains its original tension and is halved produces its octave. This applies to all stringed instruments including the piano and violin.

There are a variety of fret designs. Jumbo frets are higher and wider than normal frets and require less fretboard contact to sound a clear note. Medium frets are closer to the board and must be firmly in contact with the fretboard to sound a clear note. Some guitarist prefer jumbo frets due to the ease with which you can bend strings and the faster play offered by less fretboard contact. As with many design elements of the guitar this is a subjective area that is more personal preference rather than advantage. Good technique is not dependent on fret size

The first fret is the one nearest the nut. Some manufacturers place a zero fret immediately after the nut and the strings sit on the zero fret. This brings the sound of the open strings nearer to the quality of a fretted note.

A fretboard may have decorative inlays at the 3rd, 5th, 7th, 9th and 12th frets which serve as markers for the positions of the guitar. Fretboard inlays can be highly decorative or simple shapes and on expensive guitars may be made from exotic material like mother of pearl or abalone.

Head
The headstock lies at the end of the guitar's neck. The purpose of the headstock is to support the tuners, which terminates the strings of the instrument. The tuners are attached to tuning pegs and this allows the guitarist to lower or raise the pitch of the string. A secondary purpose of the headstock is identification and many guitar manufacturers choose to use a distinctive headstock shape often in combination with the name of the model and a trademark logo. On some guitars the model name and trademark logo may be created using inlaid materials though decals are also commonly used.

Neck
The neck can be a single piece of wood or several pieces glued together and cut to shape. The fretboard is a separate piece of wood that is attached to the neck. Necks can be glued to the body (set neck) or bolted on. Set necks are usually found on acoustic guitars and many other instruments including the violin, lute and cello. The bolt-on neck is a design feature more commonly associated with electric guitars. Most necks are wood though alternative materials such as carbon fibre composites have been used.

Nuts
All strings pass through a nut at the headstock end of the fretboard. Its function is to maintain correct string spacing and alignment so that the strings feed into their respective tuning pegs. On acoustic guitars the nut and saddle are usually made of the same material. Electric guitars commonly use plastic or synthetic nuts though sometimes metal is used. As tremolo bars can cause tuning problems, guitars equipped with them usually have some manner of locking nut, where the strings are clamped down.

Tip: Some guitarists lubricate the nut grooves so that the strings move more smoothly. You can do this at home with a soft graphite pencil. There's no need for excessive marking with the pencil just a few swipes through the groove should deposit enough graphite.

Pick Guard
Guitars, in common with all wood instruments, are prone to dents, scratches and wear. A pick guard (also known as a scratch plate) protects the body of the guitar at the point of most contact. Some electric guitars have raised pick guards so your pick is directed out and away from the pots and strings. Pick guards sometimes need replacing due to wear or damage. In the case of an expensive or rare guitar, which may have a tortoise shell pick guard, the guitar will have to be sent to an experienced luthier.

Sound Hole
Sound holes are found on all acoustics. Their purpose is to allow the air pressure to stay equalized so that the soundboard can vibrate. Archtop guitars have f-shaped sound holes - a design feature they share with the violin, viola, cello and double bass. Round sound holes usually have a decorated edge based on a geometrical design known as a rosette. On modern guitars these decorations are machine-made though some luthiers of expensive guitars still use the traditional method of laying by hand small pieces of exotic material like mother of pearl.

Truss Rod
Steel-strung guitars, whether acoustic or electric, have a metal truss rod that runs the length of the neck under the fretboard. Strengthening the neck with a truss rod counteracts the tension exerted by the strings and allows the curvature of the neck to be adjusted. Classical guitars do not require a truss rod due to the lower tension of nylon strings. Some less expensive steel-string acoustics do not have a truss rod. Adjusting the truss rod can have a marked impact on the tuning and playability of a guitar.

Truss rod adjustments should be performed with great care as it is possible to damage the neck or the truss rod. Overtightening is especially to be avoided because if the truss rod snaps or its threads strip, a very involved repair job will be necessitated. For this reason, the truss rod nut should only be tightened one quarter turn at a time. It should then be left alone for a day so the neck has time to assume the new shape. If further adjustment is necessary, repeat the process – a quarter turn, max. If one is not mechanically inclined, truss rod adjustment should be deferred to someone who is, including perhaps a guitar repair-person.

Tuning Pegs
The strings are tensioned by means of tuning pegs, also known as tuners, tuning machines, or machine heads. A high gear ratio gives smoother, easier tuning but is not essential. A guitar can be tuned successfully even with fairly cheap tuners. Most guitar tuning problems originate in other areas, especially string sticking in the nut slots, and dirty or worn strings.

Due to the tension of the strings and the constant turning of the pegs the screws that secure the tuners to the headstock may loosen. It is recommended that you check that they are screwed in tightly though avoid over-tightening which may cause alignment problems or damage the screw head or the wood.

Pickup

A pickup is a magnet wrapped in a coil of wire. When a string is plucked the vibration of the string causes the magnetic flux to vary, inducing a voltage in the coil. This is then amplified and played through a speaker.

Humbucking pickups use two coils having opposite polarity, placed in magnetic fields of opposite direction. The result is that the signal from the strings is doubled, while electromagnetic noise from other sources is cancelled. Thus humbucking pickups, or "humbuckers", have less hum and other objectionable noise pickup than single-coil pickups. However, having two coils in series, their inductance is generally higher, which decreases their high-frequency response so they sound less bright than single-coils. Humbuckers are also less able to reproduce very high harmonic frequencies of the string because their magnetic field is less localised than the field of a single coil pickup.

Active pickups are pickups with a built in preamplifier. This can reduce noise pickup and reduce signal losses in the guitar cord. Against these advantages must be weighed cost and the fact that a power source must be provided for the preamplifier. The power source can be a 9 volt battery on the guitar, or "phantom power" piped in via the guitar cord.

Passive single coils are the standard pickup for Fender Stratocasters. They have a bright and twangy clean sound but traditionally have a relatively low output voltge. They are susceptible to noise pickup from transformers – including the transformer in your amp –, neon signs, and other AC electrical equipment. This may or may not be a critical problem, depending on your physical location, and on whether you use a clean sound or a sound with a lot of amplifier compression/distortion which will make electromagnetic noise pickup more noticeable and more of a problem. Some single coils, such as the P-90, are larger than regular single coils, and thus warmer than a standard single coil. However they still retain more of a single coil sound and still can pick-up background hum. Another single coil design is the Lipstick, commonly found on Danelectro Guitars, where the entire pickup is placed in a metal enclosure with a small gap left between the two metal halves. Lipstick pickups tend to be bright sounding and the metal case results in some reduction of hum. Active single-coils can have higher output and enhanced sensitivity.

Humbuckers provide a warm and fat sound. They typically have a higher output voltage than single-coils which suits them to overdriving an amplifier so as to create a heavy sound with lots of sustain and distortion. Some humbuckers allow coil tap (using only one of the coils) or parallel connection which provides a sound similar to a single coil.

Pickups of every type are found in all genres of music, although single-coils, with their bright, twangy sound are often associated with country; and humbuckers producing thick, warm sounds with the rhythm playing in rock. In heavy metal music, humbuckers are the norm because of the necessity of having a low-noise pickup when the amplifier gain is so high.

Pickup Arrangements
There are many different arrangements for pickups. The most basic is a single pickup near the bridge.

 * S + S - the original Telecaster design uses two single coils. Telecasters have a percussive twang with lots of treble. Even when using thick single coils, as found on the Fender Jazzmaster and Gibson Les Paul P90, the tone is more emphasized on the treble side.

 * S + S + S - three single coils are standard on Fender Stratocasters and Stratocaster copies.
 * H + S + S - used on Stratocasters which are often called Fat Strats to distinguish them from the standard three single coil Stratocaster. The pick-up at the bridge is replaced by a humbucker. A favourite with guitarists who want the clean tone of single coils and the hum-free fat tone of a humbucker.
 * H + H - the standard configuration for the Gibson Les Paul. Also known as the Double Fat Strat configuration when mounted on a Stratocaster body.

 * H + S + H - found on the Steve Vai signature model by Ibanez and a favourite pickup arrangement for metal guitarists. Stratocasters using this configuration are called Super Strats.

 * H + H + H - the standard pickup arrangement for the Gibson Firebird VII, SG Custom and Les Paul

Pickup Selector
Every electric guitar, except those with a single pickup, has a pickup selector. Guitars with two pickups have a three-way switch which allows the guitarist to select either the neck pickup or the bridge pickup. When the switch is in the middle position both pickups are used.

On guitars with three pickups there is usually a five way switch. The positions are:

 * neck pickup
 * neck-middle
 * middle pickup
 * middle-bridge
 * bridge pickup

Tremolo Bar
A tremolo bar alters the pitch of the strings. Pushing down on the bar lowers the pitch of the strings and pulling up raises the pitch. Rapidly pushing and releasing will produce a modulation in pitch called vibrato. Vibrato is often confused with tremolo, a volume modulation effect found on amplifiers, hence the misnomer tremolo bar. Originally used just for vibrato; the modern improvements in guitar design, amplifiers and effects has allowed guitarists to create a new palette of tremolo bar sound effects like the popular dive bomb.

There are four kinds of tremolo:

 * Bigsby tremolo - fitted at the bottom end of the body and with a limited pitch bend on both up and down. These distinctive looking tremolos are normally found on archtop guitars. Because of its limited range, it holds its tuning and is more stable than other non-locking tremolos that allow wider pitch bends.

 * Vintage synchronized tremolo - (sometimes called the strat-type tremolo) can only down bend. This type of tremolo is more stable than the floating bridge tremolo though still prone to tuning problems.

 * Floating bridge tremolo - this design allows wide bends of a tone or more in either direction though this greatly affects tuning stability. Poorly designed floating bridges on cheap guitars should be avoided since the flexibility of the design demands the highest quality in construction and components to ensure tuning stability.

 * Floyd Rose locking tremolo - this design locks the strings therefore ensuring that the original tension of the strings are not affected by the tremolo bar and the strings return to their original tension after use. The locking tremolo makes changing strings and tuning slightly more complicated though once in tune the locking tremolo maintains tuning stability far better than non-locking designs. You still need to check your tuning every time you play since tuning is affected by other factors, such as moving from a cold room to a hot room, and the locking tremolo does not negate these factors.

Pots
Almost all electric guitars have at least two pots (potentiometers) to control the volume and tone. The usual tone control circuit uses the inductance of the pickup's coil in conjunction with an additional capacitor to reduce high frequencies when the pot is turned counterclockwise. Near the minimum position (at about 2 or 3 out of 10) there is usually a noticeable midrange peak or nasality resulting from the capacitor and inductor resonating with each other. This is a distinctive sound not easily achieved with the tone controls of the amplifier alone. A Fender Stratocaster will typically have one master volume pot and two tone pots for the neck pickup and middle pickup.

Electric Guitar Necks
This section describes the different methods used for attaching the neck to an electric guitar:

Bolt-on neck - the neck is attached to the body with bolts which are held by a mounting plate for increased stability. The mounting plate can make accessing the higher frets difficult so some manufacturers, notably Ibanez, use a hidden plate. The bolt-on neck is a standard design used by Fender.

Set neck - the neck is attached to the body with adhesive. This is the method used on acoustics and rarely is it used for mass-produced electrics. Electric guitars that feature a set neck have to be built to a high standard since once glued on the neck is permanent and cannot be adjusted. Set necks are commonly found on more costly electric guitars. Gibson and Epiphone use set necks which is claimed to have these advantages over a bolt-on neck:

 * warmer tone
 * more sustain
 * better access to higher frets

Thru-body neck - the neck extends the entire length of the body. The strings, fretboard, pickups and bridge are all mounted on the thru-body neck. The ears or wings (the bouts) are attached or glued to the central stick. The wings may be book-matched in order to give a symmetrical appearance.

The thru-body neck is usually found on high-end guitars since the design is not favoured by mass-production manufacturers. It is more common on basses than guitars. The thru-body neck allows easier access to the higher frets because there is no heel and is considered by some guitarists to offer greater sustain.

גיטרה/הכרת מבנה הגיטרה

title: Guitar/Anatomy of a Guitar


text:
User:Cyclop

While getting a degree in Biotechnology, I spend my laziness in programming simple Python, being happy with Linux, encouraging the Open Source philosophy everywhere. Also a lover of indie rock, good literature and philosophy of science. And ethanol too.

title: User:Cyclop


text:
Biochemistry/Proteins/Introduction

Protein role and importance
Proteins are among the fundamental molecules of biology. They are common to all life present on Earth today, and are responsible for most of the complex functions that make life possible. They are also the major structural constituent of living beings. According to the /Central Dogma/ of Molecular Biology (proposed by Francis Crick in 1958), information is transferred from DNA to RNA to proteins. DNA functions as a storage medium for the information necessary to synthesize proteins, and RNA is responsible for (among other things) the translation of this information into protein molecules, as part of the ribosome.

Virtually all the complex chemical functions of the living cell are performed by protein-based catalysts called enzymes. Specifically, enzymes either make or break chemical bonds. Protein enzymes should not be confused with RNA-based enzymes (also called ribozymes), a group of macromolecules that perform functions similar to protein enzymes. Further, most of the scaffolding that holds cells and organelles together is made of proteins. In addition to their catalytic functions, proteins can transmit and commute signals from the extracellular environment, duplicate genetic information, assist in transforming the energy in light and chemicals with astonishing efficiency, convert chemical energy into mechanical work, and carry molecules between cell compartments.

Functions not performed by proteins
Proteins do so much that it's important to note what proteins don't do. Currently there are no known proteins that can directly replicate themselves. Prions are no exception to this rule. It is theorized that prions may be able to act as a structural template for other chemically (but not structurally) identical proteins, but they can't function as a native template for protein synthesis de novo. Proteins don't act as fundamental energy reserves in most organisms, as their metabolism is slower and inefficient compared to sugars or lipids. They are, on the other hand, a fundamental nitrogen and amino acid reserve for many organisms. Proteins do not directly function as a membrane in most organisms, except viruses; however, they are often important components of these structures, lending both stability and structural support.

=Proteins as polymers of amino acids=

Composition and Features
Proteins are composed of a linear (not branched and not forming rings) polymer of amino acids. The twenty genetically encoded amino acids are molecules that share a central core: The α-carbon is bonded to a primary amino (-NH2) terminus, a carboxylic acid (-COOH) terminus, a hydrogen atom, and the amino acid side chain, also called the "R-group". The R-group determines the identity of the amino acid. In an aqueous solution, at physiological pH (~6.8), the amino group will be in the protonated -NH3+ form, and the carboxylic acid will be in the deprotonated -COO- form, forming a zwitterion. Most amino acids that make up proteins are L-isomers, although a few exotic creatures use D-isomers in their proteins. It is important to note that levorotatory (L) and dextrorotatory (D) are not specific to rectus (R) and sinister (S) configurations. A levorotatory form of a protein can be either R or S configuration. Levorotatory and dextrorotatory refer to how the proteins bend light in a polarimeter.

Amino acids polymerize via peptide bonds, which is a type of amide bond. A peptide bond is formed upon the dehydration of the carboxy-terminus of one amino acid with the amine terminus of a second amino acid. The resulting carbonyl group's carbon atom is directly bound to the nitrogen atom of a secondary amine. A peptide chain will have an unbound amino group free at one end (called the N-terminus) and a single free carboxylate group at the other end (called the C-terminus).

The written list of the amino acids linked together in a protein, in order, is called its primary structure. By convention, peptide sequences are written from N-terminus to C-terminus. This convention mimics the way polypeptides are synthesized by the ribosome in the cell. Small polymers of less than 20 amino acids long are more often called peptides or polypeptides. Proteins can have sequences as short as 20-30 amino acids to gigantic molecules of more than 3,000 amino acids (like Titin,a human muscle protein).

Genetically-Encoded Amino Acids
While there are theoretically billions of possible amino acids, most proteins are formed of only 20 amino acids: the genetically-encoded (or more precisely, proteogenic) amino acids. Note that all amino acids except glycine have a chiral center at their α-carbons. (Glycine has two hydrogens on its α-carbon, and therefore it is achiral.) Besides glycine, all proteogenic amino acids are L -amino acids, meaning they have the same absolute configuration as L -glyceraldehyde. This is the same as the S-configuration, with the exception of cysteine, which contains a sulfur atom in its side chain, and so the naming priority changes. D -amino acids are sometimes found in nature, as in the cell walls of certain bacteria, but they are rarely incorporated into protein chains.

The side-chains of proteogenic amino acids are quite varied: they range from a single hydrogen atom (as for glycine, the simplest amino acid) to the indole heterocycle, as found in tryptophan. There are polar, charged and hydrophobic amino acids. The chemical richness of amino acids is at the base of the complexity and versatility of proteins.

Post-Translational Modification
There are two major types of post-translational modifications to protein: those that cleave the bonds of the peptide backbone and those that add or remove functional groups to the sidechains of individual amino acids. In the first type of post-translational modification, specialized enzymes called proteases recognize specific amino acids of a protein and break the associated peptide bond, thereby irreversibly modifying the primary structure. In the second major type of modification, the amino acid side chains of a given protein are chemically modified by enzymatic reactions or are spontaneously formed (non-enzymatic). Examples of sidechain modifications are quite numerous, but common ones include oxidation, acylation, glycosylation (addition of a glycan, or sugar), methylation, and phosphorylation. Both types of post-translational modifications are capable of exerting positive and negative control over a given protein or enzyme.

The importance of protein structure
Generally speaking, the function of a protein is completely determined by its structure. Molecules like DNA, which perform a fairly small set of functions, have an almost fixed structure that's fairly independent from sequence. By contrast, protein molecules perform functions as different as digesting sugars or moving muscles. To perform so many different functions, proteins come in many different structures. The protein function is almost completely dependent on protein structure. Enzymes must recognize and react with their substrates with precise positioning of critical chemical groups in the three-dimensional space. Scaffold proteins must be able to precisely dock other proteins or components and position them in space in the correct fashion. Structural proteins like Collagen must face mechanical stresses and be able to build a regular matrix where cells can adhere and proliferate. Motor proteins must reversibly convert chemical energy in movement, in a precise fashion.

Protein folding depends on sequence
As Anfinsen demonstrated in the 1960's, proteins acquire their structure by spontaneous folding of the polypeptide chain into the minimal energy configuration. Most proteins require no external factors in order to fold (although specialized protein exist in cells, called chaperones, that help other, misfolded, proteins acquire their correct structure) — the protein sequence itself uniquely determines the structure. Often the whole process takes place in milliseconds. Despite the apparent chemical simplicity of proteins, the vast number of permutations of twenty amino acids in a linear sequence leads to an amazing number of different protein folds. Nevertheless, protein structures share several characteristics in common: they are almost all built of a few secondary structure elements (short-range structural patterns that are recurrent in protein structures) and even the way these elements combine is often repeated in common motifs. Nonetheless, it is still impossible to know what structure a given protein sequence will yield in solution. This is known as the protein folding problem, and it is one of the most important open problems in modern molecular biology.

Protein denaturation
Proteins can lose their structure if put in unsuitable chemical (e.g. high or low pH; high salt concentrations; hydrophobic environment) or physical (e.g. high temperature; high pressure) conditions. This process is called denaturation. Denatured proteins have no defined structure and, especially if concentrated, tend to aggregate into insoluble masses. Protein denaturation is by no means an exotic event: a boiled egg becomes solid just because of denaturation and subsequent aggregation of its proteins. Denatured proteins can sometimes refold when put again in the correct environment, but sometimes the process is irreversible (especially after aggregation: the boiled egg is again an example). It is finally the proteins which are responsible for susceptibility or resistance to a pathogen or parasite.

Proteins can fold into domains
A significant number of proteins, especially large proteins, have a structure divided into several independent domains. These domains can often perform specific functions in a protein. For example, a cell membrane receptor might have an extracellular domain to bind a target molecule and an intracellular domain that binds other proteins inside the cell, thereby transducing a signal across the cell membrane.

The domain of a protein is determined by the secondary structure of a protein there are four main types of domain structures: alpha-helix, beta-sheet, beta-turns, and random coil.

The alpha-helix is when the polypeptide chain forms a helix shape with the amino acids side chains sticking out, usually about 10 amino acids long. The alpha-helix gets its strength by forming internal hydrogen bonds, that occur between amino acid 1 and 4 along the length of the helix. A high concentration of Glycine's in a row tend towards the alpha-helix conformation.

The beta-sheet structure is composed of poly-peptide chains stacking forming hydrogen bonds between the sheets. You can form parallel sheets by stacking in the same direction N-C terminal on top of N-C terminal or form anti-parallel by stacking in opposite directions N-C terminal on top of C-N terminal. Beta-turns link two anti-parallel beta strands by a 4 amino acid loop in a defined conformation.

A random coil is a portion of the protein that has no defined secondary structure.

Domains of a protein then come from unique portions of the peptide that are made up of these types of secondary structure.

title: Biochemistry/Proteins/Introduction


text:
Biochemistry/Proteins/The chemistry of proteins

General features
Amino acids consist of a primary amine bound to an aliphatic carbon atom (the so-called α-carbon), which in turn is bound to a carboxylic acid group. At least one hydrogen atom is bound to the α-carbon; in addition, the α-carbon bears a side chain, which is different for different amino acids. In a neutral aqueous solution, amino acids exist in two forms. A very small fraction of amino acid molecules will be neutral, with a deprotonated amino group and a protonated carboxylic acid group. However, the overwhelming majority of molecules will be in a Zwitterion tautomer, with a positive charge on the (protonated) amino group and a negative charge on the (deprotonated) carboxylate group.

Amino acids are linked via a Peptide bond. (From an organic chemistry perspective, a peptide bond is a type of amide group.) A peptide bond consists of a carbonyl group's carbon atom directly bound to the nitrogen atom of a secondary amine. A peptide chain will have an unbound amino group free at one end (called the N-terminus) and a single free carboxylate group at the other end (called the C-terminus).

The peptide bond is planar, because resonance between the carbonyl group and the amino nitrogen lends the C-N bond a partial double-bond character. (It is possible to draw a resonance structure with a double bond between the carbon atom and the nitrogen atom, with a formal negative charge on the oxygen atom and a formal positive charge on the nitrogen.) This prevents rotation around the C-N bond, locking the peptide bond in the trans conformation, and holding six atoms in a plane: the α-carbon of one amino acid, the carbonyl carbon and oxygen atoms, the amino nitrogen and hydrogen atoms, and the &alpha-carbon of the second amino acid are all co-planar.

The structure of a peptide chain's "backbone" can be described uniquely by the torsion angles between adjacent peptide units. The φ-angle is the torsion angle between the α-carbon and the carbonyl carbon of one amino acid; the ψ-angle is the torsion angle between the amino nitrogen and the α-carbon.

''Peptide bond formation Two amino acids with different side chains react when the amino-terminus (red) of one joins the carboxy-terminus (blue) of another are linked by an amide bond (green). See also the mechanism of peptide bond formation.''

It is important to note that the formation of this peptide bond is highly unfavorable under standard conditions. However, in the human body, there are enzymes that assist in facilitating this reaction, making peptide bond formation and proteins possible.

Chemical classification of aminoacids
The 20 amino acids encoded by the genetic code are:

They are not shown in their zwitterionic state for clarity. At physiological pH (~pH 6.8), all would be so, except proline, which is a five-membered ring. Charged side-chains are shown ionic when they exist as such at physiological pH.

Protein Electrophoresis
Protein Electrophoresis is a method in which a mixture of proteins can be separated and analyzed. Electrophoresis is based on the mobility of ions in an electric field. The charge distribution of the molecules is critical in the separation of all electrophoresis. In an electric field, electrophoresis is a passage of charged molecules in solution. Positively charged ions have tendency toward a negative electrode and inversely, negatively charged ions have tendency toward a positive electrode. The molecular weight results to a molecular friction which is directly proportional to the molecular charge and its voltage and inversely proportional to a molecule's mobility in an electric field.

Gel electrophoresis is performed to analyze the molecular weights and the charge of the protein and is mostly used in electrophoresis of the protein. The gel electrophoresis is carried out in a thin piece of polyacrylamide. The crosslinked of acrylamide and N,N'-methylene-bis-acrylamide forms the polyacrylamide by polymerization. The size has an important effect in the movement of the protein molecule. The smaller molecules of protein would result in a faster passage of the molecules through the gel pores.

The separation of the protein molecules in the gel affects the protein activity. In this process, first the protein reduces the disruption of disulfide bonding by heating which results in purification and denaturalization. Next, the sodium dodecyl sulfate, abbreviated as SDS, (and ionic detergent) is added. SDS is an anionic detergent which dissolve hydrophobic molecules and denatures protein molecules without breaking peptide bonds. This result in the dislocation of the structure of the protein changes the secondary, tertiary and quaternary to the primary structure with negative charge. Then the protein is passed through the gel. For denatured proteins, SDS can form a steady charge mass ratio in binding with proteins.

The polyacrylamide gel electrophoresis is a very sensitive method capable of a bearing a high resolution and it is analytically used in the studies in the separation techniques.

Isoelectric point
The isoelectric point (pI) is the pH-value in which a protein is neutral, that is, has zero net charge. To be clear, it is not the pH value where a protein has all bases deprotonated and all acids protonated, but rather the value where positive and negative charges cancel out to zero.

Calculating pI: An aminoacid with n ionizable groups with their respective pKa values pK1, pK2, ... pkn will have the pI equal to the average of the group pkas:

pI=(pK1+pK2+...+pkn)/n

Most proteins have many ionizable sidechains in addition to their amino- and carboxy- terminal groups. The pI is different for each protein and it can be theoretically calculated according Henderson-Hasselbalch equation if we know amino acids composition of protein.

In order to experimentally determine a protein's pI 2-Dimensional Electrophoresis (2-DE) can be used. The proteins of a cell lysate are applied to a pH immobilized gradient strip, upon electrophoresis the proteins migrate to their pI within the strip. The second dimension of 2-DE is the separation of proteins by MW using a SDS-gel. To clearly understand isoelectric point, you have to keep in mind that the positively charged groups are balanced by the negatively charged groups. For simple amino acid " alanine", the isoelectric point is an average of the PKa of the carboxyl with PK1 of (2.34) and ammonium with PK2 of (9.69) groups. So, the PI for the simple amino acid " alanine" is calculated as:(2.34+9.69)/2 which is equal to 6.02. When additional basic or acidic groups are added as a side-chain functions, the isoelectric point pI will be the average of the pKa's of the most similar acids. Example for this concept could be aspartic acid in which the similar acids are alpha-carboxyl function with pKa of 2.1 and the side chain carboxyl function with a pKa of 3.9. Thus, the pI for aspartic acid is (2.1+3.9)/2=3.0. Another example is arginine, its similar acids are guanidinium on the side chain with pKa of 12.5 and the alpha-ammonium function with pKa of 9.0. Thus the calculated pI for arginine= (12.5+9.0)/2=10.75. pI does not has a unite.

The peptidic bond
Two amino acid molecules can be covalently joined through a substituted amide linkage, termed a peptide bond, to yield a dipeptide. this link is formed by dehydration (removal of the water molecules - one hydrogen atom from one amino acid and an OH group from the other). This process can then continue to join other amino acids and yield in an amino acid chain. When there are few amino acids in a chain, it is called an oligopeptide, when there are many it is called a polypeptide. although the terms "protein" and "polypeptide" are sometimes used to describe the same thing, the term polypeptide is generally used when the molecular weight of the chain is below 10,000. An amino acid unit in a peptide is often called a residue.

Disulfide bonds
Disulfide bonds form between the sulfur atoms of two cysteine side chains in a protein. The side chains undergo a reversible oxidation of the sulfhydryl groups of the cysteine, which results in covalent bonding of the sulfur atoms (S-S). This bonding is called a "disulfide bridge". Typically, disulfides don't form on the surface of proteins because of the presence of reducing agents in the cytoplasm. These bonds are of great importance concerning the shaping of protein structure; their formation guides the folding of peptide chains as the proteins are produced. Structural proteins that have to be rigorously stable (for example, Keratin, which is found in nail, horn and crustacean shell) often contain a large number of disulfide bonds.

Post-translational modifications
After a protein is synthesized inside the cell, it is usually modified by the addition of extra functional groups to the polypeptide chain. These can be sugar or phosphate groups and may confer to the protein special functions such as: the ability to recognize other molecules, to integrate in the plasma membrane, to catalyze biochemical reactions, and various other processes. It is in the interest of the biochemist to understand what proteins are modified, what the modification is, and where it is located. An easy way to do this is by using mass spectrometry. In a sample of protein submitted to mass spectrometry you will see both modified and unmodified protein signals. The change in mass between these signals will correspond to the change in mass of your protein due to your post-translation modification.


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Biochemistry/Proteins/Protein structure and folding

What is protein folding?
Protein folding is commonly a fast or very fast process, often but not always reversible, taking no more than a few milliseconds to occur. It can be viewed as a complex compromise between the different chemical interactions that can happen between the amino acid sidechains, the amidic backbone and the solvent. There are literally millions of possible three-dimensional configurations, often with minimal energetic differences between them. That's why we're still almost unable to predict the folding of a given polypeptide chain ab initio.Protein folding problem is that scientist still has failed to crack the code that governs folding. Moreover, the ability of biological polymers such as protein fold into well-defined structures is remarkable thermodynamically. An unfolded polymer exists are random coils, each copy of an unfolded polymers will have different conformation, yielding a mixture of many possible conformation.

Folding depends only on primary structure
In 1954 Christian Anfinsen demonstrated that the folding of a protein in a given environment depends only on its primary structure - the amino acid sequence. This conclusion was by no means obvious, given the complexity of the folding process and the paucity of biochemical knowledge at the time. The process of folding often begins co-translationally, so that the N-terminus of the protein begins to fold while the C-terminal portion of the protein is still being synthesized by the ribosome. Specialized proteins called chaperones assist in the folding of other proteins. Meanwhile, protein folding is a thermodynamically driven process: that is, proteins fold by reaching their thermodynamically most stable structure. The path followed by the protein in the potential energy landscape is far from obvious, however. Many local and non-local interactions take part in the process, and the space of possible structures is enormous. As of today molecular dynamics simulations are giving invaluable hints on the first stages of the folding process. It is known now that the unfolded state still retains key long-range interactions and that the local propensity of the sequence to fold in a given secondary structure element narrow the "search" in the so-called conformational space. This seems to mean that biological proteins somehow evolved to properly fold. In fact, many random amino acid sequences only acquire ill-defined structures (molten globules) or no structure at all.

There are some general rules, however. Hydrophobic amino acids will tend to be kept inside the structure, with little or no contact with the surrounding water; conversely, polar or charged amino acids will be often exposed to solvent. Very long proteins will often fold in various distinct modules, instead of in a single large structure.

The Ramachandran plot
The Ramachandran plot was invented by professor G.N.Ramachandran, a very eminent scientist from India. He discovered the triple helix structure of collagen in 1954 a year after the double helix structure was put forth. In a polypeptide the main chain N-Calpha and Calpha-C bonds relatively are free to rotate. These rotations are represented by the torsion angles phi and psi, respectively.

G N Ramachandran used computer models of small polypeptides to systematically vary phi and psi with the objective of finding stable conformations. For each conformation, the structure was examined for close contacts between atoms. Atoms were treated as hard spheres with dimensions corresponding to their van der Waals radii. Therefore, phi and psi angles which cause spheres to collide correspond to sterically disallowed conformations of the polypeptide backbone

Intramolecular forces in protein folding
The tertiary structure is held together by hydrogen bonds, hydrophilic interactions, ionic interactions, and/or disulfide bonds.

The protein folding problem
The protein folding problem relates to what is known as the Levinthal paradox. Levinthal calculated that if a fairly small protein is composed of 100 amino acids and each amino acid residue has only 3 possible conformations (an underestimate) then the entire protein can fold into 3100-1 or 5x1047 possible conformations. Even if it takes only 10-13 of a second to try each conformation it would take 1027 years to try them all. Obviously a protein doesn't take that long to fold, so randomly trying out all possible conformations is not the way proteins fold. Since most proteins fold on a timescale of the order of milliseconds it is clear that the process is directed in some manner dependent on the constituents of the chain. The protein folding problem which has perplexed scientists for over thirty years is that of understanding how the tertiary structure of a protein is related to its primary structure, because it has been proven that the primary structure of a protein holds the only information necessary for the protein to fold. Ultimately the aim is also to be able to predict what pathway the protein will take.

Folding in extreme environments
Most proteins are not capable of maintaining their three-dimensional shape when they are exposed to environmental extremes such as a low or high pH, or a highly variable temperature.

Changes in the pH of the proteins environment may alter the charges on the amino acid side chains that form the whole protein, so that repulsive or attractive forces may form, altering the secondary and tertiary structure of the protein as a whole, as a result the shape of the enzyme is warped, and the now non-functional protein is said to be denatured.

A high or exceptionally low temperature can cause the constitutive bonds on the protein to be broken, again resulting in the protein being rendered non-functional.

It is important to note that certain proteins, mainly digestive enzymes such as trypsin, are capable of with-standing a pH as low as 1. If the pH of such an enzymes environment were to increase to approximately pH5, it would be inactivated.

Protein misfolding
The way that a protein folds is one of the most important factors influencing its properties, as this is what determines which active groups are exposed for interaction. If the protein misfolds, its properties can be markedly changed. One example of this is in Transmissible Spongiform Encephalopathies, such as BSE, and Scrapie. In these, the prion protein, which is involved in the brain's copper metabolism, misfolds, and starts forming plaques, which destroy brain tissue.

=Protein structural levels= Biochemists refer to four distinct aspects of a protein's structure:

Primary structure
Primary structure is practically a synonym of the amino acid sequence. It can also contain informations on amino acids linked by peptide bonds. Primary structure is typically written as a string of three letter sequences, each representing an amino acid. Peptides and proteins must have the correct sequence of amino acids.

Secondary structure
Secondary structure elements are elementary structural patterns that are present in most,if not all,known proteins. These are highly patterned sub-structures --alpha helix and beta sheet-- consisting of loops between elements or segments of polypeptide chain that assume no stable shape. Secondary structure elements, when mapped on the sequence and depicted in the relative position they have in respect to each other, define the topology of the protein. It is also relevant to note that hydrogen bonding between residues is the cause for secondary structure features; secondary structure is usually described to beginning biochemists as (almost) entirely independent of residue side-chain interactions.

Tertiary structure
Tertiary structure is the name given to refer to the overall shape of a single protein molecule. Although tertiary structure is sometimes described (especially to beginning biology and biochemistry students) as being a result of interactions between amino acid residue side chains, a more correct understanding of tertiary structure is the interactions between elements of secondary protein structure, i.e. alpha-helices and beta-pleated sheets. Tertiary structure is often referred to as the "fold structure" of a protein, since it is the result of the complex three-dimensional interplay of other structural and environmental elements.

Super-tertiary structure (protein modules)
Some literature refers to elements of super-tertiary structure, which often refers to elements of folding that, for whatever reason, do not neatly fit into the category of tertiary structure. Often this level of distinction is saved for graduate level coursework. Protein denaturation can be a reversible or an irreversible process, i.e., it may be possible or impossible to make the protein regain its original spatial conformation.

Quaternary structure
Quaternary structure is the shape or structure that results from the union of more than one protein molecule, usually called subunit proteins subunits in this context, which function as part of the larger assembly or protein complex. And it refers to the regular association of two or more polypeptide chains to form a complex. A multi-subunit protein may be composed of two or more identical polypeptides, or it may include different polypeptides. Quaternary structure tends to be stabilized mainly by weak interactions between residues exposed on surfaces polypeptides within a complex.

=Secondary structure elements=

The alpha helix
The alpha helix is a periodic structure formed when main-chain atoms from residues spaced four residues apart hydrogen bond with one another. This gives rise to a helical structure, which in natural proteins is always right-handed. Each turn of the helix comprises 3.6 amino acids. Alpha helices are stiff, rod-like structures which are found in many unrelated proteins. One feature of these structures is that they tend to show a bias in the distribution of hydrophobic residues such that they tend to occur primarily on one face of the helix.

The amino acids in an α helix are arranged in a helical structure, about 5 Å wide. Each amino acid results in a 100° turn in the helix, and corresponds to a translation of 1.5Å along the helical axis. The helix is tightly packed; there is almost no free space within the helix. All amino acid side-chains are arranged at the outside of the helix. The N-H group of amino acid (n) can establish a hydrogen bond with the C=O group of amino acid (n+4).

Short polypeptides usually are not able to adopt the alpha helical structure, since the entropic cost associated with the folding of the polypeptide chain is too high. Some amino acids (called helix breakers) like proline will disrupt the helical structure.

Ordinarily, a helix has a buildup of positive charge at the N-terminal end and negative charge at the C-terminal end which is a destabilizing influence. As a result, α helices are often capped at the N-terminal end by a negatively charged amino acid (like glutamic acid) in order to stabilize the helix dipole. Less common (and less effective) is C-terminal capping with a positively charged protein like lysine.

α helices have particular significance in DNA binding motifs, including helix-turn-helix motifs, leucine zipper motifs and zinc finger motifs. This is because of the structural coincidence of the α helix diameter of 12Å being the same as the width of the major groove in B-form DNA.

α helices are one of the basic structural elements in proteins, together with beta sheets.

The peptide backbone of an α helix has 3.6 amino acids per turn.

The beta sheet
The β sheet (also β-pleated sheet) is a commonly occurring form of regular secondary structure in proteins, first proposed by Linus Pauling and Robert Corey in 1951. It consists of two or more amino acid sequences within the same protein that are arranged adjacently and in parallel, but with alternating orientation such that hydrogen bonds can form between the two strands. The amino acid chain is almost fully extended throughout a β strand, lessening the probability of bulky steric clashes. The Ramachandran plot shows optimal conformation with angle phi = -120 to -60 degrees and angle psi = 120 to 160 degrees. The N-H groups in the backbone of one strand establish hydrogen bonds with the C=O groups in the backbone of the adjacent, parallel strand(s). The cumulative effect of multiple such hydrogen bonds arranged in this way contributes to the sheet's stability and structural rigidity and integrity: for example, cellulose's beta-1,4 glucose structure. The side chains from the amino acid residues found in a β sheet structure may also be arranged such that many of the adjacent side chains on one side of the sheet are hydrophobic, while many of those adjacent to each other on the alternate side of the sheet are polar or charged (hydrophilic). Some sequences involved in a β sheet, when traced along the backbone, take a hairpin turn in orientation (direction), sometimes through one or more prolines. The α-C atoms of adjacent strands stand 3.5Å apart. In addition to the parallel beta sheet, there is also the anti-parallel beta sheet. The hydrogen-bond still exists in this conformation but the main difference lies in the directionality of the protein. In this conformation the proteins run in opposite directions, but the resulting hydrogen bonds connect directly across from one another instead of the diagonal. In short, beta sheets can be purely parallel, anti-parallel, or even mixed.

The random coil
A protein that completely lacks secondary structure is a random coil. In random coil, the only fixed relationship between amino acids is that between adjacent residues through the peptide bond. As a result, random coil can be detected from the absence of the signals in a multidimensional nuclear magnetic resonance experiment that depend on particular peptide-peptide interactions. Likewise in the images produced in crystallography experiments, pieces of random coil appear simply as an absence of "electron density" or contrast. Random coil is also easily distinguished by circular dichroism. Denaturing reduces a protein entirely to random coil.

Less common secondary structure elements
Certain other periodic structures rarely appear in proteins, some of which are similar to the more common types. For example, two variants of the alpha-helix also occur, the 3-10 helix and the pi helix. These have helical pitches of 3 and 4.4 residues per turn respectively, corresponding to hydrogen bonds forming between residue i and i+3 for the 3-10 helix and between i and i+5 for the pi helix. Both are usually very short (1 turn or so) and have been seen only at the ends of alpha helices.

=Tertiary structure elements=

Alpha-only structures
Structures that contain only Alpha Helices

Beta-only structures
=Common folds and modules=

The Rossman fold
The Rossmann fold is a protein structural motif found in proteins that bind nucleotides, especially the cofactor NAD. The structure is composed of three or more parallel beta strands linked by two alpha helices in the topological order beta-alpha-beta-alpha-beta. Because each Rossmann fold can bind one nucleotide, binding domains for dinucleotides such as NAD consist of two paired Rossmann folds that each bind one nucleotide moiety of the cofactor molecule. Single Rossmann folds can bind mononucleotides such as the cofactor FMN.

The motif is named for Michael Rossmann who first pointed out that this was a frequently occurring motif in nucleotide binding proteins.

Keratin
Found in hair and in the palms of human hands.