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Colin Powell

Colin Luther Powell (April 5, 1937 – October 18, 2021) was an American politician, statesman, diplomat, and United States Army officer who was the 65th United States secretary of state from 2001 to 2005. He was the first Black secretary of state. He was the 15th United States national security advisor from 1987 to 1989, and the 12th chairman of the Joint Chiefs of Staff from 1989 to 1993.

Powell was born in New York City in 1937 to parents who immigrated from Jamaica. He was raised in the South Bronx and educated in the New York City public schools, earning a bachelor's degree in geology from the City College of New York (CCNY). He also participated in ROTC (Army Reserve Officer Training Corps) at CCNY and received a commission as an Army second lieutenant on graduation in June 1958. He was a professional soldier for 35 years, holding many command and staff positions and rising to the rank of four-star general. He was commander of the U.S. Army Forces Command in 1989.

Powell's last military assignment, from October 1989 to September 1993, was as Joint Chiefs of Staff chairman, the highest military position in the United States Department of Defense. During this time, he oversaw twenty-eight crises, including the invasion of Panama in 1989 and Operation Desert Storm in the Persian Gulf War against Iraq in 1990–1991. He formulated the Powell Doctrine, which limits American military action unless it satisfies criteria regarding American national security interests, overwhelming force, and widespread public support. He served as secretary of state under Republican president George W. Bush. As secretary of state, Powell gave a presentation to the United Nations Security Council regarding the rationale for the Iraq War, but he later admitted that the speech contained substantial inaccuracies. He was forced to resign after Bush was reelected in 2004.

In 1995, Powell wrote his autobiography, My American Journey and then in retirement another book titled, It Worked for Me: Lessons in Life and Leadership (2012). He pursued a career as a public speaker, addressing audiences across the country and abroad. Before his appointment as Secretary of State he chaired America's Promise. In the 2016 United States presidential election, Powell, who was not a candidate, received three electoral votes from Washington state for the office of President of the United States. He won numerous U.S. and foreign military awards and decorations. His civilian awards included the Presidential Medal of Freedom (twice), the Congressional Gold Medal, the Presidential Citizens Medal, and the Secretary's Distinguished Service Award. Powell died from complications of COVID-19 in 2021, while being treated for a form of blood cancer that damaged his immune system.

Early life
Colin Luther Powell was born on April 5, 1937, in Harlem, a neighborhood in the New York City borough of Manhattan. He was born to Jamaican immigrants Maud Ariel (née McKoy) and Luther Theophilus Powell. His parents were both of mixed African and Scottish ancestry. Luther worked as a shipping clerk and Maud as a seamstress. Powell was raised in the South Bronx and attended the now closed Morris High School, from which he graduated in 1954.

While at school, Powell worked at a local baby furniture store, where he picked up Yiddish from the Eastern European Jewish shopkeepers and some of the customers. He also served as a Shabbos goy, helping Orthodox families with needed tasks on the Sabbath. He received a bachelor of science degree in geology from the City College of New York in 1958 and said that he was a "C average" student. "I wasn't doing well in civil engineering". While at CCNY, Powell shifted his study focus to the Reserve Officers' Training Corps (ROTC) and became a "straight A student" in it. Powell also graduated from George Washington University with an MBA in 1971 and an honorary doctor of public service in 1990.

He held the distinction of being the first chairman to have attained his commission through the ROTC.

Despite his parents' pronunciation of his name as, Powell pronounced his name   from childhood on after the World War II flyer Colin P. Kelly Jr.

Military career
Powell was a professional soldier for thirty-five years, holding a variety of command and staff positions and rising to the rank of general.

Training
While attending the City College of New York, Powell joined the Reserve Officers' Training Corps (ROTC). He described the experience as one of the happiest experiences of his life. According to Powell: "It was only once I was in college, about six months into college when I found something that I liked, and that was ROTC, Reserve Officer Training Corps in the military. And I not only liked it, but I was pretty good at it. That's what you really have to look for in life, something that you like, and something that you think you're pretty good at. And if you can put those two things together, then you're on the right track, and just drive on."

As a cadet, Powell joined the Pershing Rifles, the ROTC fraternal organization and drill team begun by General John Pershing.

Early career
Upon graduation, he received a commission as an Army second lieutenant; at this time, the Army was newly desegregated. He underwent training in the state of Georgia, where he was refused service in bars and restaurants because of the color of his skin. After attending basic training at Fort Benning, Powell was assigned to the 48th Infantry, in West Germany, as a platoon leader. From 1960 to 1962, he served as group liaison officer, company executive officer, and commander of Company A, 1st Battle Group, 4th Infantry, 2nd Infantry Brigade, 5th Infantry Division (Mechanized) at Fort Devens, Massachusetts.

Vietnam War
Captain Powell served a tour in Vietnam as a South Vietnamese Army (ARVN) advisor from 1962 to 1963. While on patrol in a Viet Cong-held area, he was wounded by stepping on a punji stake. The large infection made it difficult for him to walk, and caused his foot to swell for a short time, shortening his first tour.

Powell returned to Vietnam as a major in 1968, serving as assistant chief of staff of operations for the 23rd (Americal) Infantry Division. During the second tour in Vietnam he was decorated with the Soldier's Medal for bravery after he survived a helicopter crash and single-handedly rescued three others, including division commander Major General Charles M. Gettys, from the burning wreckage.

Mỹ Lai massacre inquiry
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Powell was charged with investigating a detailed letter by 11th Light Infantry Brigade soldier Tom Glen, which backed up rumored allegations of the 1968 Mỹ Lai massacre. Powell wrote: "In direct refutation of this portrayal is the fact that relations between Americal soldiers and the Vietnamese people are excellent." Later, Powell's assessment would be described as whitewashing the news of the massacre, and questions would continue to remain undisclosed to the public. In May 2004, Powell said to television and radio host Larry King, "I was in a unit that was responsible for My Lai. I got there after My Lai happened. So, in war, these sorts of horrible things happen every now and again, but they are still to be deplored."

After the Vietnam War
When he returned to the U.S. from Vietnam in 1971, Powell earned a Master of Business Administration degree from George Washington University in Washington, D.C. He later served a White House Fellowship under President Richard Nixon from 1972 to 1973. During 1975–1976 he attended the National War College, Washington, D.C.

In his autobiography, My American Journey, Powell named several officers he served under who inspired and mentored him. As a lieutenant colonel commanding 1st Battalion, 32nd Infantry in South Korea, Powell was very close to his division commander, Major General Henry "Gunfighter" Emerson, whom he regarded as one of the most caring officers he ever met. Emerson insisted his troops train at night to fight a possible North Korean attack, and made them repeatedly watch the television film Brian's Song to promote racial harmony. Powell always professed that what set Emerson apart was his great love of his soldiers and concern for their welfare. After a race riot occurred, in which African-American soldiers almost killed a white officer, Powell was charged by Emerson to crack down on black militants; Powell's efforts led to the discharge of one soldier, and other efforts to reduce racial tensions. During 1976–1977 he commanded the 2nd Brigade of the 101st Airborne Division.

Powell subsequently served as the junior military assistant to deputy secretaries of defense Charles Duncan and Graham Claytor, receiving a promotion to brigadier general on June 1, 1979. At the ceremony, he received from Secretary Harold Brown's protocol officer, Stuart Purviance, a framed quotation by President Abraham Lincoln. The quote was "I can make a brigadier general in five minutes. But it's not so easy to replace one hundred ten horses." Taped to the back of the frame was an envelope with instructions that it not be opened for ten years. When Powell opened the note in 1989, after he had become Chairman of the Joint Chiefs of Staff, he read Purviance's prediction that Powell would become Chief of Staff of the United States Army. Powell wrote that he kept the Lincoln quote as a reminder to remain humble despite his rank and position.

National Security Advisor and other advisory roles
Powell retained his role as the now-senior military assistant into the presidency of Ronald Reagan, serving under Claytor's successor as deputy secretary of defense, Frank Carlucci. Powell and Carlucci formed a close friendship, referring to each by first names in private, as Powell refused any sort of first-name basis in an official capacity. It was on Powell's advice that newly-elected President Ronald Reagan presented Roy Benavidez the Medal of Honor; Benavidez had received the Distinguished Service Cross, which his commander argued should be upgraded, but army officials believed there was no living eyewitness to testify to Benavidez's heroism. A soldier who had been present during the action in question learned in July 1980 of the effort to upgrade Benavidez's medal and provided the necessary sworn statement; the upgrade to the Medal of Honor was approved in December 1980. Powell also declined an offer from Secretary of the Army John O. Marsh Jr. to be his under secretary due to his reluctance to assume a political appointment; James R. Ambrose was selected instead. Intent on attaining a division command, Powell petitioned Carlucci and Army chief of staff Edward C. Meyer for reassignment away from the Pentagon, with Meyer appointing Powell as assistant division commander for operations and training of the 4th Infantry Division at Fort Carson, Colorado under Major General John W. Hudachek.

After he left Fort Carson, Powell became the senior military assistant to Secretary of Defense Caspar Weinberger, whom he assisted during the 1983 invasion of Grenada and the 1986 airstrike on Libya. Under Weinberger, Powell was also involved in the unlawful transfer of U.S.-made TOW anti-tank missiles and Hawk anti-aircraft missiles from Israel to Iran as part of the criminal conspiracy that would later become known as the Iran–Contra affair. In November 1985, Powell solicited and delivered to Weinberger a legal assessment that the transfer of Hawk missiles to Israel or Iran, without Congressional notification, would be "a clear violation" of the law. Despite this, thousands of TOW missiles and hundreds of Hawk missiles and spare parts were transferred from Israel to Iran until the venture was exposed in a Lebanese magazine, Ash-Shiraa, in November 1986. According to Iran-Contra Independent Counsel Lawrence E. Walsh, when questioned by Congress, Powell "had given incomplete answers" concerning notes withheld by Weinberger and that the activities of Powell and others in concealing the notes "seemed corrupt enough to meet the new, poorly defined test of obstruction." Following his resignation as Secretary of Defense, Weinberger was indicted on five felony charges, including one count Obstruction of Congress for concealing the notes. Powell was never indicted by the Independent Counsel in connection with the Iran-Contra affair.

In 1986, Powell took over the command of V Corps in Frankfurt, Germany, from Robert Lewis "Sam" Wetzel. The next year, he served as United States Deputy National Security Advisor, under Frank Carlucci.

Following the Iran–Contra scandal, Powell became, at the age of 49, Ronald Reagan's National Security Advisor, serving from 1987 to 1989 while retaining his Army commission as a lieutenant general. He helped negotiate a number of arms treaties with Mikhail Gorbachev, the leader of the Soviet Union.

In April 1989, after his tenure with the National Security Council, Powell was promoted to four-star general under President George H. W. Bush and briefly served as the Commander in Chief, Forces Command (FORSCOM), headquartered at Fort McPherson, Georgia, overseeing all active U.S. Army regulars, U.S. Army Reserve, and National Guard units in the Continental U.S., Hawaii, and Puerto Rico. He became the third general since World War II to reach four-star rank without ever serving as a division commander, joining Dwight D. Eisenhower and Alexander Haig.

Later that year, President George H. W. Bush selected him as Chairman of the Joint Chiefs of Staff.

Chairman of the Joint Chiefs of Staff

Powell's last military assignment, from October 1, 1989, to September 30, 1993, was as the 12th chairman of the Joint Chiefs of Staff, the highest military position in the Department of Defense. At age 52, he became the youngest officer, and first Afro-Caribbean American, to serve in this position. Powell was also the first JCS chair who received his commission through ROTC.

During this time, Powell oversaw responses to 28 crises, including the invasion of Panama in 1989 to remove General Manuel Noriega from power and Operation Desert Storm in the 1991 Persian Gulf War. During these events, Powell earned the nickname "the reluctant warrior" – although Powell himself disputed this label, and spoke in favor of the first Bush administration's Gulf War policies.

As a military strategist, Powell advocated an approach to military conflicts that maximizes the potential for success and minimizes casualties. A component of this approach is the use of overwhelming force, which he applied to Operation Desert Storm in 1991. His approach has been dubbed the Powell Doctrine. Powell continued as chairman of the JCS into the Clinton presidency. However, as a realist, he considered himself a bad fit for an administration largely made up of liberal internationalists. He clashed with then-U.S. ambassador to the United Nations Madeleine Albright over the Bosnian crisis, as he opposed any military intervention that did not involve U.S. interests.

Powell also regularly clashed with Secretary of Defense Leslie Aspin, whom he was initially hesitant to support after Aspin was nominated by President Clinton. During a lunch meeting between Powell and Aspin in preparation of Operation Gothic Serpent, Aspin was more focused on eating salad than listening and paying attention to Powell's presentation on military operations. The incident caused Powell to grow more irritated towards Aspin and led to his early resignation on September 30, 1993. Powell was succeeded temporarily by Vice Chairman of the Joint Chiefs of Staff Admiral David E. Jeremiah, who took the position as Acting Chairman of the Joint Chiefs of Staff. Soon after Powell's resignation, on October 3–4, 1993, the Battle of Mogadishu, the aim of which was to capture Somali warlord Mohamed Farrah Aidid, was initiated and ended in disaster. Powell later defended Aspin, saying in part that he could not fault Aspin for Aspin's decision to remove a Lockheed AC-130 from the list of armaments requested for the operation.

Powell took an early resignation from his tenure as Chairman of the Joint Chiefs of Staff on September 30, 1993.

The following year President Clinton sent newly-retired Powell, together with former President Jimmy Carter and Senator Sam Nunn, to visit Haiti in an effort to persuade General Raoul Cédras and the ruling junta to abdicate in favor of former Haitian President Aristide, under the threat of an imminent US invasion to remove them by force. Powell status as a retired general well known and respected in Haiti was held to be instrumental in persuading Gen. Cédras.

During his chairmanship of the JCS, there was discussion of awarding Powell a fifth star, granting him the rank of General of the Army. But even in the wake of public and Congressional pressure to do so, Clinton-Gore presidential transition team staffers decided against it.

National Security Advisor and other advisory roles
Powell retained his role as the now-senior military assistant

Potential presidential candidate
Powell's experience in military matters made him a very popular figure with both American political parties. Many Democrats admired his moderate stance on military matters, while many Republicans saw him as a great asset associated with the successes of past Republican administrations. Put forth as a potential Democratic vice presidential nominee in the 1992 U.S. presidential election or even potentially replacing Vice President Dan Quayle as the Republican vice presidential nominee, Powell eventually declared himself a Republican and began to campaign for Republican candidates in 1995. He was touted as a possible opponent of Bill Clinton in the 1996 U.S. presidential election, possibly capitalizing on a split conservative vote in Iowa and even leading New Hampshire polls for the GOP nomination, but Powell declined, citing a lack of passion for politics. Powell defeated Clinton 50–38 in a hypothetical match-up proposed to voters in the exit polls conducted on Election Day. Despite not standing in the race, Powell won the Republican New Hampshire Vice-Presidential primary on write-in votes.

In 1997, Powell founded America's Promise with the objective of helping children from all socioeconomic sectors. That same year saw the establishment of The Colin L. Powell Center for Leadership and Service. The mission of the center is to "prepare new generations of publicly engaged leaders from populations previously underrepresented in public service and policy circles, to build a strong culture of civic engagement at City College, and to mobilize campus resources to meet pressing community needs and serve the public good."

Powell was mentioned as a potential candidate in the 2000 U.S. presidential election, but again decided against running. Once Texas Governor George W. Bush secured the Republican nomination, Powell endorsed him for president and spoke at the 2000 Republican National Convention. Bush won the general election and appointed Powell as secretary of state in 2001.

In the electoral college vote count of 2016, Powell received three votes for president from faithless electors from the state of Washington.

Secretary of State (2001–2005)
President-elect George W. Bush named Powell as his nominee to be secretary of state in a ceremony at his ranch in Crawford, Texas on December 16, 2000. This made Powell the first person to formally accept a Cabinet post in the Bush administration, as well the first black United States secretary of state. As secretary of state, Powell was perceived as moderate. Powell was unanimously confirmed by the United States Senate by voice vote on January 20, 2001, and ceremonially sworn in on January 26. Over the course of his tenure he traveled less than any other U.S. Secretary of State in thirty years. This is partly attributed to a letter from former diplomat George F. Kennan, who advised Powell to focus on his duties as the president's principal foreign policy advisor and avoid trips that risked undercutting the duties of the ambassadors.

On September 11, 2001, Powell was in Lima, Peru, meeting with President Alejandro Toledo and attending a meeting of foreign ministers of the Organization of American States. After the September 11 attacks, Powell's job became of critical importance in managing the United States of America's relationships with foreign countries to secure a stable coalition in the War on Terrorism.

2003 U.S. invasion of Iraq
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Powell came under fire for his role in building the case for the 2003 invasion of Iraq. A 2004 report by the Iraq Survey Group concluded that the evidence that Powell offered to support the allegation that the Iraqi government possessed weapons of mass destruction (WMDs) was inaccurate. As early as 2000 on the day Powell was nominated to be Secretary of State he told the press "Saddam is sitting on a failed regime that is not going to be around in a few years time".

In a press statement on February 24, 2001, Powell had said that sanctions against Iraq had prevented the development of any weapons of mass destruction by Saddam Hussein. Powell favored involving the international community in the invasion, as opposed to a unilateral approach.

Powell's chief role was to garner international support for a multi-national coalition to mount the invasion. To this end, Powell addressed a plenary session of the United Nations Security Council on February 5, 2003, to argue in favor of military action. Citing numerous anonymous Iraqi defectors, Powell asserted that "there can be no doubt that Saddam Hussein has biological weapons and the capability to rapidly produce more, many more." Powell also stated that there was "no doubt in my mind" that Saddam was working to obtain key components to produce nuclear weapons. Powell stated that he gave his speech to the UN on "four days' notice".

Britain's Channel 4 News reported soon afterwards that a British intelligence dossier that Powell had referred to as a "fine paper" during his presentation had been based on old material and plagiarized an essay by American graduate student Ibrahim al-Marashi.

A Senate report on intelligence failures would later detail the intense debate that went on behind the scenes on what to include in Powell's speech. State Department analysts had found dozens of factual problems in drafts of the speech. Some of the claims were taken out, but others were left in, such as claims based on the yellowcake forgery. The administration came under fire for having acted on faulty intelligence, particularly that which was single-sourced to the informant known as Curveball. Powell later recounted how Vice President Dick Cheney had joked with him before he gave the speech, telling him, "You've got high poll ratings; you can afford to lose a few points." Powell's longtime aide-de-camp and Chief of Staff from 1989 to 2003, Colonel Lawrence Wilkerson, later characterized Cheney's view of Powell's mission as to "go up there and sell it, and we'll have moved forward a peg or two. Fall on your damn sword and kill yourself, and I'll be happy, too."

In September 2005, Powell was asked about the speech during an interview with Barbara Walters and responded that it was a "blot" on his record. He went on to say, "It will always be a part of my record. It was painful. It's painful now."

Wilkerson later said that he inadvertently participated in a hoax on the American people in preparing Powell's erroneous testimony before the United Nations Security Council.

As recounted in Soldier: The Life of Colin Powell, in 2001 before 9/11, Richard A. Clarke, a National Security Council holdover from the Clinton administration, pushed the new Bush administration for action against al-Qaeda in Afghanistan, a move opposed by Paul Wolfowitz who advocated for the creation of a "U.S.-protected, opposition-run 'liberated' enclave around the southern Iraqi city of Basra". Powell referred to Wolfowitz and other top members of Donald Rumsfeld's staff "as the 'JINSA crowd,' " in reference to the pro-Israel Jewish Institute for National Security Affairs. Again invoking "the JINSA crowd" Powell also attributed the decision to go to war in Iraq in 2003 to the neoconservative belief that regime change in Baghdad "was a first and necessary stop on the road to peace in Jerusalem."

A review of Soldier by Tim Rutten criticized Powell's remarks as a "blot on his record", accusing Powell of slandering "neoconservatives in the Defense Department – nearly all of them Jews" with "old and wholly unmeritorious allegations of dual loyalty". A 2007 article about fears that Jewish groups "will be accused of driving America into a war with the regime in Tehran" cited the DeYoung biography and quoted JINSA's then-executive director, Thomas Neumann, as "surprised" Powell "would single out a Jewish group when naming those who supported the war." Neumann said, "I am not accusing Powell of anything, but these are words that the antisemites will use in the future".

Once Saddam Hussein had been deposed, Powell's renewed role was to once again establish a working international coalition, this time to assist in the rebuilding of post-war Iraq. On September 13, 2004, Powell testified before the Senate Governmental Affairs Committee, acknowledging that the sources who provided much of the information in his February 2003 UN presentation were "wrong" and that it was "unlikely" that any stockpiles of WMDs would be found. Claiming that he was unaware that some intelligence officials questioned the information prior to his presentation, Powell pushed for reform in the intelligence community, including the creation of a national intelligence director who would assure that "what one person knew, everyone else knew".

Other foreign policy issues
Additionally, Powell was critical of other aspects of U.S. foreign policy in the past, such as its support for the 1973 Chilean coup d'état that deposed the democratically elected president Salvador Allende in favor of Augusto Pinochet. From two separate interviews in 2003, Powell stated in one about the 1973 event: "I can't justify or explain the actions and decisions that were made at that time. It was a different time. There was a great deal of concern about communism in this part of the world. Communism was a threat to the democracies in this part of the world. It was a threat to the United States." In another interview, he also simply stated: "With respect to your earlier comment about Chile in the 1970s and what happened with Mr. Allende, it is not a part of American history that we're proud of."

In the Hainan Island incident of April 1, 2001, a United States US EP-3 surveillance aircraft collided mid-air with a Chinese Shenyang J-8 jet fighter over the South China Sea. While somewhat ambiguous, Powell's expression of "very sorry" was accepted as sufficient for the formal apology that China had sought. The incident was nonetheless a serious flare-up in United States-China relations and created negative feelings towards the United States by the Chinese public and increased public feelings of Chinese nationalism.

In September 2004, Powell described the Darfur genocide as "genocide", thus becoming the first cabinet member to apply the term "genocide" to events in an ongoing conflict.

In November the president "forced Powell to resign", according to Walter LaFeber. Powell announced his resignation as Secretary of State on November 15, 2004, shortly after Bush was reelected. Bush's desire for Powell to resign was communicated to Powell via a phone call by Bush's chief of staff, Andrew Card. The following day, Bush nominated National Security Advisor Condoleezza Rice as Powell's successor.

In mid-November, Powell stated that he had seen new evidence suggesting that Iran was adapting missiles for a nuclear delivery system. The accusation came at the same time as the settlement of an agreement between Iran, the IAEA, and the European Union.

Although biographer Jeffrey J. Matthews is highly critical of how Powell misled the United Nations Security Council regarding weapons of mass destruction in Iraq, he credits Powell with a series of achievements at the State Department. These include restoration of morale to psychologically demoralized professional diplomats, leadership of the international HIV/AIDS initiative, resolving a crisis with China, and blocking efforts to tie Saddam Hussein to the 9/11 attacks on the United States.

Life after diplomatic service
After retiring from the role of Secretary of State, Powell returned to private life. In April 2005, he was privately telephoned by Republican senators Lincoln Chafee and Chuck Hagel, at which time Powell expressed reservations and mixed reviews about the nomination of John Bolton as ambassador to the United Nations, but refrained from advising the senators to oppose Bolton (Powell had clashed with Bolton during Bush's first term). The decision was viewed as potentially dealing significant damage to Bolton's chances of confirmation. Bolton was put into the position via a recess appointment because of the strong opposition in the Senate.

On April 28, 2005, an opinion piece in The Guardian by Sidney Blumenthal (a former top aide to President Bill Clinton) claimed that Powell was in fact "conducting a campaign" against Bolton because of the acrimonious battles they had had while working together, which among other things had resulted in Powell cutting Bolton out of talks with Iran and Libya after complaints about Bolton's involvement from the British. Blumenthal added that "The foreign relations committee has discovered that Bolton made a highly unusual request and gained access to 10 intercepts by the National Security Agency. Staff members on the committee believe that Bolton was probably spying on Powell, his senior advisors and other officials reporting to him on diplomatic initiatives that Bolton opposed."

In September 2005, Powell criticized the response to Hurricane Katrina, and said thousands of people were not properly protected because they were poor, rather than because they were black.

On January 5, 2006, he participated in a meeting at the White House of former Secretaries of Defense and State to discuss United States foreign policy with Bush administration officials. In September 2006, Powell sided with more moderate Senate Republicans in supporting more rights for detainees and opposing President Bush's terrorism bill. He backed Senators John Warner, John McCain, and Lindsey Graham in their statement that U.S. military and intelligence personnel in future wars will suffer for abuses committed in 2006 by the U.S. in the name of fighting terrorism. Powell stated that "The world is beginning to doubt the moral basis of our fight against terrorism."

In 2007, he joined the board of directors of Steve Case's new company Revolution Health. Powell also served on the Council on Foreign Relations Board of directors.

In 2008, Powell served as a spokesperson for National Mentoring Month, a campaign held each January to recruit volunteer mentors for at-risk youth.

Soon after Barack Obama's 2008 election, Powell began being mentioned as a possible cabinet member. He was not nominated.

In September 2009, Powell advised President Obama against surging U.S. forces in Afghanistan. The president announced the surge the following December.

In 2010, Powell joined the Smithsonian advisory council. Together with his wife, Alma Powell, they are the founding donors who offer their support to the museum's capital campaign and Living History campaign. He was an advocate for the National Museum of African American History and Culture.

On March 14, 2014, Salesforce.com announced that Powell had joined its board of directors.

Political positions
During his early political career through his tenure within the Joint Chiefs of Staff, Powell was an independent. Powell was a moderate Republican from 1995 until 2021. Many have described Powell as a neoconservative for his foreign policy positions, although Powell never personally acknowledged the label. In 2021, Powell recanted his status as a Republican following the January 6 United States Capitol attack. The attack moved Powell to call for president Trump's resignation, noting: "I wish he would do what Nixon did and just step down. Somebody ought to go up to him and it's over." Powell also accused Trump of attempting to "overthrow the government", and that Trump's false claims of a stolen election were "dangerous for our democracy". Powell was pro-choice regarding abortion, and expressed some support for an assault weapons ban. He stated in his autobiography that he supported affirmative action that levels the playing field, without giving a leg up to undeserving persons because of racial issues. Powell originally suggested the don't ask, don't tell policy to President Clinton, though he later supported its repeal as proposed by Robert Gates and Admiral Mike Mullen in January 2010, saying "circumstances had changed".

Powell gained attention in 2004 when, in a conversation with British Foreign Secretary Jack Straw, he reportedly referred to neoconservatives within the Bush administration as "fucking crazies".

In a September 2006 letter to John McCain, Powell expressed opposition to President Bush's push for military tribunals of those formerly and currently classified as enemy combatants. Specifically, he objected to the effort in Congress to "redefine Common Article 3 of the Geneva Convention." He also asserted: "The world is beginning to doubt the moral basis of our fight against terrorism."

Defending the Iraq War
At the 2007 Aspen Ideas Festival in Colorado, Powell stated that he had spent two and a half hours explaining to President Bush "the consequences of going into an Arab country and becoming the occupiers". During this discussion, he insisted that the U.S. appeal to the United Nations first, but if diplomacy failed, he would support the invasion: "I also had to say to him that you are the President, you will have to make the ultimate judgment, and if the judgment is this isn't working and we don't think it is going to solve the problem, then if military action is undertaken I'm with you, I support you."

In a 2008 interview on CNN, Powell reiterated his support for the 2003 decision to invade Iraq in the context of his endorsement of Barack Obama, stating: "My role has been very, very straightforward. I wanted to avoid a war. The president [Bush] agreed with me. We tried to do that. We couldn't get it through the U.N. and when the president made the decision, I supported that decision. And I've never blinked from that. I've never said I didn't support a decision to go to war."

Powell's position on the Iraq War troop surge of 2007 was less consistent. In December 2006, he expressed skepticism that the strategy would work and whether the U.S. military had enough troops to carry it out successfully. He stated: "I am not persuaded that another surge of troops into Baghdad for the purposes of suppressing this communitarian violence, this civil war, will work." Following his endorsement of Barack Obama in October 2008, however, Powell praised General David Petraeus and U.S. troops, as well as the Iraqi government, concluding that "it's starting to turn around". By mid-2009, he had concluded a surge of U.S. forces in Iraq should have come sooner, perhaps in late 2003.

Endorsement of Barack Obama
Powell donated the maximum allowable amount to John McCain's campaign in the summer of 2007 and in early 2008, his name was listed as a possible running mate for Republican nominee McCain's bid during the 2008 U.S. presidential election.

McCain won the Republican presidential nomination, but the Democrats nominated the first black candidate, Senator Barack Obama of Illinois. On October 19, 2008, Powell announced his endorsement of Obama during a Meet the Press interview, citing "his ability to inspire, because of the inclusive nature of his campaign, because he is reaching out all across America, because of who he is and his rhetorical abilities", in addition to his "style and substance." He additionally referred to Obama as a "transformational figure". Powell further questioned McCain's judgment in appointing Sarah Palin as the vice presidential candidate, stating that despite the fact that she is admired, "now that we have had a chance to watch her for some seven weeks, I don't believe she's ready to be president of the United States, which is the job of the vice president." He said that Obama's choice for vice president, Joe Biden, was ready to be president. He also added that he was "troubled" by the "false intimations that Obama was Muslim." Powell stated that "[Obama] is a Christian – he's always been a Christian... But the really right answer is, what if he is? Is there something wrong with being a Muslim in this country? The answer's no, that's not America." Powell then mentioned Kareem Rashad Sultan Khan, a Muslim American soldier in the U.S. Army who served and died in the Iraq War. He later stated, "Over the last seven weeks, the approach of the Republican Party has become narrower and narrower [...] I look at these kind of approaches to the campaign, and they trouble me." Powell concluded his Sunday morning talk show comments with "It isn't easy for me to disappoint Sen. McCain in the way that I have this morning, and I regret that [...] I think we need a transformational figure. I think we need a president who is a generational change and that's why I'm supporting Barack Obama, not out of any lack of respect or admiration for Sen. John McCain." Later in a December 12, 2008, CNN interview with Fareed Zakaria, Powell reiterated his belief that during the last few months of the campaign, Palin pushed the Republican party further to the right and had a polarizing impact on it.

When asked why he was still a Republican on Meet the Press he said, "I'm still a Republican. And I think the Republican Party needs me more than the Democratic Party needs me. And you can be a Republican and still feel strongly about issues such as immigration, and improving our education system, and doing something about some of the social problems that exist in our society and our country. I don't think there's anything inconsistent with this."

Views on the Obama administration
In a July 2009 CNN interview with John King, Powell expressed concern over President Obama increasing the size of the federal government and the size of the federal budget deficit. In September 2010, he criticized the Obama administration for not focusing "like a razor blade" on the economy and job creation. Powell reiterated that Obama was a "transformational figure." In a video that aired on CNN.com in November 2011, Colin Powell said in reference to Barack Obama, "many of his decisions have been quite sound. The financial system was put back on a stable basis."

On October 25, 2012, 12 days before the presidential election, he gave his endorsement to President Obama for re-election during a broadcast of CBS This Morning. He considered the administration to have had success and achieved progress in foreign and domestic policy arenas. As additional reasons for his endorsement, Powell cited the changing positions and perceived lack of thoughtfulness of Mitt Romney on foreign affairs, and a concern for the validity of Romney's economic plans.

In an interview with ABC's Diane Sawyer and George Stephanopoulos during ABC's coverage of President Obama's second inauguration, Powell criticized members of the Republican Party who spread "things that demonize the president". He called on GOP leaders to publicly denounce such talk.

2016 e-mail leaks and criticism of Donald Trump
Powell was very vocal on the state of the Republican Party. Speaking at a Washington Ideas forum in early October 2015, he warned the audience that the Republican Party had begun a move to the fringe right, lessening the chances of a Republican White House in the future. He also remarked on Republican presidential candidate Donald Trump's statements regarding immigrants, noting that there were many immigrants working in Trump hotels.

In March 2016, Powell denounced the "nastiness" of the 2016 Republican primaries during an interview on CBS This Morning. He compared the race to reality television, and stated that the campaign had gone "into the mud."

In August 2016, Powell accused the Hillary Clinton campaign of trying to pin her email controversy on him. Speaking to People magazine, Powell said, "The truth is, she was using [the private email server] for a year before I sent her a memo telling her what I did."

On September 13, 2016, emails were obtained that revealed Powell's private communications regarding both Donald Trump and Hillary Clinton. Powell privately reiterated his comments regarding Clinton's email scandal, writing, "I have told Hillary's minions repeatedly that they are making a mistake trying to drag me in, yet they still try," and complaining that "Hillary's mafia keeps trying to suck me into it" in another email. In another email discussing Clinton's controversy, Powell said she should have told everyone what she did "two years ago", and said that she has not "been covering herself with glory." Writing on the 2012 Benghazi attack controversy surrounding Clinton, Powell said to then U.S. Ambassador Susan Rice, "Benghazi is a stupid witch hunt." Commenting on Clinton in a general sense, he mused that "Everything HRC touches she kind of screws up with hubris", and in another email stated "I would rather not have to vote for her, although she is a friend I respect."

Powell called Donald Trump a "national disgrace", with "no sense of shame". He wrote of Trump's role in the birther movement, which he called "racist". He suggested the media ignore Trump: "To go on and call him an idiot just emboldens him." The emails were obtained by the media as the result of a hack.

Powell endorsed Clinton on October 25, 2016, stating it was "because I think she's qualified, and the other gentleman is not qualified".

Despite not running in the election, Powell received three electoral votes for president from faithless electors in Washington who had pledged to vote for Clinton, coming in third overall. After Barack Obama, he was the second black person to receive electoral votes in a presidential election.

Views on the Trump administration
In an interview in October 2019, Powell warned that the GOP needed to "get a grip" and put the country before their party, standing up to then president Trump rather than worrying about political fallout. He said: "When they see things that are not right, they need to say something about it because our foreign policy is in shambles right now, in my humble judgment, and I see things happening that are hard to understand." On June 7, 2020, Powell announced he would be voting for former Vice President Joe Biden in the 2020 United States presidential election. In August, Powell delivered a speech in support of Biden's candidacy at the 2020 Democratic National Convention.

In January 2021, after the Capitol building was attacked by Trump supporters, Powell told CNN: "I can no longer call myself a fellow Republican."

Personal life
Powell married Alma Johnson on August 25, 1962. Their son, Michael Powell, was the chairman of the Federal Communications Commission (FCC) from 2001 to 2005. Their daughters are Linda Powell, an actress, and Annemarie Powell. As a hobby, Powell restored old Volvo and Saab automobiles. In 2013, he faced questions about his relationship with the Romanian diplomat Corina Crețu, after a hacked AOL email account had been made public. He acknowledged a "very personal" email relationship but denied further involvement. He was an Episcopalian.

Death
On October 18, 2021, Powell, who was being treated for multiple myeloma, died at Walter Reed National Military Medical Center of complications from COVID-19 at the age of 84. He had been vaccinated, but his myeloma compromised his immune system; he also had early-stage Parkinson's disease. President Joe Biden and four of the five living former presidents issued statements calling Powell as an American hero. Donald Trump released a statement saying "He made plenty of mistakes, but anyway, may he rest in peace!" and referred to him as a "classic RINO".

Present at the funeral service at the Washington National Cathedral were President Biden and former presidents Barack Obama and George W. Bush, along with First Lady Jill Biden and former first ladies Michelle Obama, Laura Bush, and Hillary Clinton (also representing her husband, former President Bill Clinton, who was unable to attend following treatment for sepsis) as well as many other dignitaries.

Powell is buried at Arlington National Cemetery in Section 60, Grave 11917.

Civilian awards and honors
Powell's civilian awards include two Presidential Medals of Freedom (the second with distinction), the Congressional Gold Medal, and the Ronald Reagan Freedom Award.

 * In 1990, Powell received the U.S. Senator John Heinz Award for Greatest Public Service by an Elected or Appointed Official, an award given out annually by Jefferson Awards.
 * In 1991, Powell was awarded the Presidential Medal of Freedom by President George H. W. Bush.
 * In 1991, Powell was awarded the Spingarn Medal from the NAACP.
 * In 1991, Powell was inducted into the Horatio Alger Association of Distinguished Americans.
 * On April 23, 1991, Powell was awarded the Congressional Gold Medal "in recognition of his exemplary performance as a military leader and advisor to the President in planning and coordinating the military response of the United States to the Iraqi invasion of Kuwait and the ultimate retreat and defeat of Iraqi forces and Iraqi acceptance of all United Nations Resolutions relating to Kuwait."
 * On September 30, 1993, Powell was awarded his second Presidential Medal of Freedom, this time with the additional "with distinction" by President Bill Clinton.
 * On November 9, 1993, Powell was awarded the second Ronald Reagan Freedom Award, by Ronald Reagan. Powell served as Reagan's National Security Advisor from 1987 to 1989.
 * In 1993, Colin Powell was created an honorary Knight Commander of the Order of the Bath by Queen Elizabeth II of the United Kingdom.
 * In 1998, he was awarded the Sylvanus Thayer Award by the United States Military Academy for his commitment to the ideals of "Duty, Honor, Country".
 * In 1998, he was elected to the American Philosophical Society
 * The 2002 Liberty Medal was awarded to Colin Powell on July 4 in Philadelphia, Pennsylvania. In his acceptance speech, Powell reminded Americans that "It is for America, the Land of the Free and the Home of the Brave, to help freedom ring across the globe, unto all the peoples thereof. That is our solemn obligation, and we will not fail."
 * In 2003, an elementary school named after Powell was opened in Centreville, Virginia. Powell visited the school in 2013.
 * In 2005, Powell received the Bishop John T. Walker Distinguished Humanitarian Service Award for his contributions to Africa.
 * Powell received the 2006 AARP Andrus Award, the Association's highest honor.
 * In 2005, Colin and Alma Powell were awarded the Woodrow Wilson Award for Public Service by the Woodrow Wilson International Center for Scholars of the Smithsonian Institution.
 * Powell was a recipient of the Silver Buffalo Award, the highest adult award given by the Boy Scouts of America.
 * A street in Gelnhausen, Germany, was named after him: "General-Colin-Powell-Straße."
 * In 2002, scholar Molefi Kete Asante listed Colin Powell on his list of 100 Greatest Blacks in America.
 * In 2009, an elementary school named for Colin Powell opened in El Paso. It is in the El Paso Independent School District, located on Fort Bliss property, and serves a portion of Fort Bliss.
 * In 2009, Powell was elected to the American Academy of Arts and Sciences
 * Powell was an honorary board member of the humanitarian organization Wings of Hope
 * From 2006, he was the chairman of the Board of Trustees for Eisenhower Fellowships.
 * In 2006, The Harry S. Truman Research Institute for the Advancement of Peace at The Hebrew University of Jerusalem awarded Colin Powell with the Truman Peace Prize for his efforts to conduct the "war against terrorism", through diplomatic as well as military means, and to avert regional and civil conflicts in many parts of the world.
 * In September 2012, Union City, New Jersey, opened Colin Powell Elementary School, which was named after Powell, and which was dedicated on February 7, 2013, with governor Chris Christie in attendance. Powell himself visited the school on June 4, 2013.
 * In 2014, Colin Powell was named to the National Board of Advisors for High Point University.
 * In 2024, Prince George's County Public Schools opened Colin L. Powell Academy, named after Powell, in Fort Washington, Maryland.

title: Colin Powell


text:
Chlorophyll

Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words $χλωρός$, ("pale green") and $φύλλον$,  ("leaf"). Chlorophyll allows plants to absorb energy from light.

Chlorophylls absorb light most strongly in the blue portion of the electromagnetic spectrum as well as the red portion. Conversely, it is a poor absorber of green and near-green portions of the spectrum. Hence chlorophyll-containing tissues appear green because green light, diffusively reflected by structures like cell walls, is less absorbed. Two types of chlorophyll exist in the photosystems of green plants: chlorophyll a and b.

History
Chlorophyll was first isolated and named by Joseph Bienaimé Caventou and Pierre Joseph Pelletier in 1817. The presence of magnesium in chlorophyll was discovered in 1906, and was the first detection of that element in living tissue.

After initial work done by German chemist Richard Willstätter spanning from 1905 to 1915, the general structure of chlorophyll a was elucidated by Hans Fischer in 1940. By 1960, when most of the stereochemistry of chlorophyll a was known, Robert Burns Woodward published a total synthesis of the molecule. In 1967, the last remaining stereochemical elucidation was completed by Ian Fleming, and in 1990 Woodward and co-authors published an updated synthesis. Chlorophyll f was announced to be present in cyanobacteria and other oxygenic microorganisms that form stromatolites in 2010; a molecular formula of C55H70O6N4Mg and a structure of (2-formyl)-chlorophyll a were deduced based on NMR, optical and mass spectra.

Photosynthesis
Chlorophyll is vital for photosynthesis, which allows plants to absorb energy from light.

Chlorophyll molecules are arranged in and around photosystems that are embedded in the thylakoid membranes of chloroplasts. In these complexes, chlorophyll serves three functions:
 * 1) The function of the vast majority of chlorophyll (up to several hundred molecules per photosystem) is to absorb light.
 * 2) Having done so, these same centers execute their second function: The transfer of that energy by resonance energy transfer to a specific chlorophyll pair in the reaction center of the photosystems.
 * 3) This specific pair performs the final function of chlorophylls: Charge separation, which produces the unbound protons (H$+$) and electrons (e$−$) that separately propel biosynthesis.

The two currently accepted photosystem units are photosystem I and photosystem II, which have their own distinct reaction centres, named P700 and P680, respectively. These centres are named after the wavelength (in nanometers) of their red-peak absorption maximum. The identity, function and spectral properties of the types of chlorophyll in each photosystem are distinct and determined by each other and the protein structure surrounding them.

The function of the reaction center of chlorophyll is to absorb light energy and transfer it to other parts of the photosystem. The absorbed energy of the photon is transferred to an electron in a process called charge separation. The removal of the electron from the chlorophyll is an oxidation reaction. The chlorophyll donates the high energy electron to a series of molecular intermediates called an electron transport chain. The charged reaction center of chlorophyll (P680+) is then reduced back to its ground state by accepting an electron stripped from water. The electron that reduces P680+ ultimately comes from the oxidation of water into O2 and H+ through several intermediates. This reaction is how photosynthetic organisms such as plants produce O2 gas, and is the source for practically all the O2 in Earth's atmosphere. Photosystem I typically works in series with Photosystem II; thus the P700+ of Photosystem I is usually reduced as it accepts the electron, via many intermediates in the thylakoid membrane, by electrons coming, ultimately, from Photosystem II. Electron transfer reactions in the thylakoid membranes are complex, however, and the source of electrons used to reduce P700+ can vary.

The electron flow produced by the reaction center chlorophyll pigments is used to pump H+ ions across the thylakoid membrane, setting up a proton-motive force a chemiosmotic potential used mainly in the production of ATP (stored chemical energy) or to reduce NADP+ to NADPH. NADPH is a universal agent used to reduce CO2 into sugars as well as other biosynthetic reactions.

Reaction center chlorophyll–protein complexes are capable of directly absorbing light and performing charge separation events without the assistance of other chlorophyll pigments, but the probability of that happening under a given light intensity is small. Thus, the other chlorophylls in the photosystem and antenna pigment proteins all cooperatively absorb and funnel light energy to the reaction center. Besides chlorophyll a, there are other pigments, called accessory pigments, which occur in these pigment–protein antenna complexes.

Chemical structure
Several chlorophylls are known. All are defined as derivatives of the parent chlorin by the presence of a fifth, ketone-containing ring beyond the four pyrrole-like rings. Most chlorophylls are classified as chlorins, which are reduced relatives of porphyrins (found in hemoglobin). They share a common biosynthetic pathway with porphyrins, including the precursor uroporphyrinogen III. Unlike hemes, which contain iron bound to the N4 center, most chlorophylls bind magnesium. The axial ligands attached to the Mg2+ center are often omitted for clarity. Appended to the chlorin ring are various side chains, usually including a long phytyl chain (C20H39O). The most widely distributed form in terrestrial plants is chlorophyll a. The only difference between chlorophyll a and chlorophyll b is that the former has a methyl group where the latter has a formyl group. This difference causes a considerable difference in the absorption spectrum, allowing plants to absorb a greater portion of visible light.

The structures of chlorophylls are summarized below:

Chlorophyll e is reserved for a pigment that has been extracted from algae in 1966 but not chemically described. Besides the lettered chlorophylls, a wide variety of sidechain modifications to the chlorophyll structures are known in the wild. For example, Prochlorococcus, a cyanobacterium, uses 8-vinyl Chl a and b.

Measurement of chlorophyll content
Chlorophylls can be extracted from the protein into organic solvents. In this way, the concentration of chlorophyll within a leaf can be estimated. Methods also exist to separate chlorophyll a and chlorophyll b.

In diethyl ether, chlorophyll a has approximate absorbance maxima of 430 nm and 662 nm, while chlorophyll b has approximate maxima of 453 nm and 642 nm. The absorption peaks of chlorophyll a are at 465 nm and 665 nm. Chlorophyll a fluoresces at 673 nm (maximum) and 726 nm. The peak molar absorption coefficient of chlorophyll a exceeds 105 M−1 cm−1, which is among the highest for small-molecule organic compounds. In 90% acetone-water, the peak absorption wavelengths of chlorophyll a are 430 nm and 664 nm; peaks for chlorophyll b are 460 nm and 647 nm; peaks for chlorophyll c1 are 442 nm and 630 nm; peaks for chlorophyll c2 are 444 nm and 630 nm; peaks for chlorophyll d are 401 nm, 455 nm and 696 nm.

Ratio fluorescence emission can be used to measure chlorophyll content. By exciting chlorophyll a fluorescence at a lower wavelength, the ratio of chlorophyll fluorescence emission at $705 nm$ and $735 nm$ can provide a linear relationship of chlorophyll content when compared with chemical testing. The ratio F735/F700 provided a correlation value of r2 0.96 compared with chemical testing in the range from 41 mg m−2 up to 675 mg m−2. Gitelson also developed a formula for direct readout of chlorophyll content in mg m−2. The formula provided a reliable method of measuring chlorophyll content from 41 mg m−2 up to 675 mg m−2 with a correlation r2 value of 0.95.

The Dualex is an optical sensor used in plant science and agriculture for the assessment of chlorophyll contents in leaves. This device allows researchers to perform real-time and non-destructive measurements.

Biosynthesis
In some plants, chlorophyll is derived from glutamate and is synthesised along a branched biosynthetic pathway that is shared with heme and siroheme. Chlorophyll synthase is the enzyme that completes the biosynthesis of chlorophyll a:
 * chlorophyllide a + phytyl diphosphate $$\rightleftharpoons$$ chlorophyll a + diphosphate

This conversion forms an ester of the carboxylic acid group in chlorophyllide a with the 20-carbon diterpene alcohol phytol. Chlorophyll b is made by the same enzyme acting on chlorophyllide b. The same is known for chlorophyll d and f, both made from corresponding chlorophyllides ultimately made from chlorophyllide a.

In Angiosperm plants, the later steps in the biosynthetic pathway are light-dependent. Such plants are pale (etiolated) if grown in darkness. Non-vascular plants and green algae have an additional light-independent enzyme and grow green even in darkness.

Chlorophyll is bound to proteins. Protochlorophyllide, one of the biosynthetic intermediates, occurs mostly in the free form and, under light conditions, acts as a photosensitizer, forming free radicals, which can be toxic to the plant. Hence, plants regulate the amount of this chlorophyll precursor. In angiosperms, this regulation is achieved at the step of aminolevulinic acid (ALA), one of the intermediate compounds in the biosynthesis pathway. Plants that are fed by ALA accumulate high and toxic levels of protochlorophyllide; so do the mutants with a damaged regulatory system.

Senescence and the chlorophyll cycle
The process of plant senescence involves the degradation of chlorophyll: for example the enzyme chlorophyllase hydrolyses the phytyl sidechain to reverse the reaction in which chlorophylls are biosynthesised from chlorophyllide a  or b. Since chlorophyllide a can be converted to chlorophyllide b and the latter can be re-esterified to chlorophyll b, these processes allow cycling between chlorophylls a and b. Moreover, chlorophyll b can be directly reduced (via 71-hydroxychlorophyll a) back to chlorophyll a, completing the cycle. In later stages of senescence, chlorophyllides are converted to a group of colourless tetrapyrroles known as nonfluorescent chlorophyll catabolites (NCC's) with the general structure:
 * [[Image:Nonfluorescentchlorophilcatabolites.svg|Nonfluorescent chlorophyll catabolites]]

These compounds have also been identified in ripening fruits and they give characteristic autumn colours to deciduous plants.

Distribution
The chlorophyll maps show milligrams of chlorophyll per cubic meter of seawater each month. Places where chlorophyll amounts were very low, indicating very low numbers of phytoplankton, are blue. Places where chlorophyll concentrations were high, meaning many phytoplankton were growing, are yellow. The observations come from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite. Land is dark gray, and places where MODIS could not collect data because of sea ice, polar darkness, or clouds are light gray. The highest chlorophyll concentrations, where tiny surface-dwelling ocean plants are thriving, are in cold polar waters or in places where ocean currents bring cold water to the surface, such as around the equator and along the shores of continents. It is not the cold water itself that stimulates the phytoplankton. Instead, the cool temperatures are often a sign that the water has welled up to the surface from deeper in the ocean, carrying nutrients that have built up over time. In polar waters, nutrients accumulate in surface waters during the dark winter months when plants cannot grow. When sunlight returns in the spring and summer, the plants flourish in high concentrations.

Culinary use
Synthetic chlorophyll is registered as a food additive colorant, and its E number is E140. Chefs use chlorophyll to color a variety of foods and beverages green, such as pasta and spirits. Absinthe gains its green color naturally from the chlorophyll introduced through the large variety of herbs used in its production. Chlorophyll is not soluble in water, and it is first mixed with a small quantity of vegetable oil to obtain the desired solution.

Biological use
A 2002 study found that "leaves exposed to strong light contained degraded major antenna proteins, unlike those kept in the dark, which is consistent with studies on the illumination of isolated proteins". This appeared to the authors as support for the hypothesis that "active oxygen species play a role in vivo" in the short-term behaviour of plants.

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

title: Chlorophyll


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Carotene

The term carotene (also carotin, from the Latin carota, "carrot" ) is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the exception of some aphids and spider mites which acquired the synthesizing genes from fungi). Carotenes are photosynthetic pigments important for photosynthesis. Carotenes contain no oxygen atoms. They absorb ultraviolet, violet, and blue light and scatter orange or red light, and (in low concentrations) yellow light.

Carotenes are responsible for the orange colour of the carrot, after which this class of chemicals is named, and for the colours of many other fruits, vegetables and fungi (for example, sweet potatoes, chanterelle and orange cantaloupe melon). Carotenes are also responsible for the orange (but not all of the yellow) colours in dry foliage. They also (in lower concentrations) impart the yellow coloration to milk-fat and butter. Omnivorous animal species which are relatively poor converters of coloured dietary carotenoids to colourless retinoids, such as humans and chickens, have yellow-coloured body fat, as a result of the carotenoid retention from the vegetable portion of their diet.

Carotenes contribute to photosynthesis by transmitting the light energy they absorb to chlorophyll. They also protect plant tissues by helping to absorb the energy from singlet oxygen, an excited form of the oxygen molecule O2 which is formed during photosynthesis.

β-Carotene is composed of two retinyl groups, and is broken down in the mucosa of the human small intestine by β-carotene 15,15'-monooxygenase to retinal, a form of vitamin A. β-Carotene can be stored in the liver and body fat and converted to retinal as needed, thus making it a form of vitamin A for humans and some other mammals. The carotenes α-carotene and γ-carotene, due to their single retinyl group (β-ionone ring), also have some vitamin A activity (though less than β-carotene), as does the xanthophyll carotenoid β-cryptoxanthin. All other carotenoids, including lycopene, have no beta-ring and thus no vitamin A activity (although they may have antioxidant activity and thus biological activity in other ways).

Animal species differ greatly in their ability to convert retinyl (beta-ionone) containing carotenoids to retinals. Carnivores in general are poor converters of dietary ionone-containing carotenoids. Pure carnivores such as ferrets lack β-carotene 15,15'-monooxygenase and cannot convert any carotenoids to retinals at all (resulting in carotenes not being a form of vitamin A for this species); while cats can convert a trace of β-carotene to retinol, although the amount is totally insufficient for meeting their daily retinol needs.

Molecular structure
Carotenes are polyunsaturated hydrocarbons containing 40 carbon atoms per molecule, variable numbers of hydrogen atoms, and no other elements. Some carotenes are terminated by rings, on one or both ends of the molecule. All are coloured, due to the presence of conjugated double bonds. Carotenes are tetraterpenes, meaning that they are derived from eight 5-carbon isoprene units (or four 10-carbon terpene units).

Carotenes are found in plants in two primary forms designated by characters from the Greek alphabet: alpha-carotene (α-carotene) and beta-carotene (β-carotene). Gamma-, delta-, epsilon-, and zeta-carotene (γ, δ, ε, and ζ-carotene) also exist. Since they are hydrocarbons, and therefore contain no oxygen, carotenes are fat-soluble and insoluble in water (in contrast with other carotenoids, the xanthophylls, which contain oxygen and thus are less chemically hydrophobic).

History
The discovery of carotene from carrot juice is credited to Heinrich Wilhelm Ferdinand Wackenroder, a finding made during a search for antihelminthics, which he published in 1831. He obtained it in small ruby-red flakes soluble in ether, which when dissolved in fats gave "a beautiful yellow colour". William Christopher Zeise recognised its hydrocarbon nature in 1847, but his analyses gave him a composition of C5H8. It was Léon-Albert Arnaud in 1886 who confirmed its hydrocarbon nature and gave the formula C26H38, which is close to the theoretical composition of C40H56. Adolf Lieben in studies, also published in 1886, of the colouring matter in corpora lutea, first came across carotenoids in animal tissue, but did not recognise the nature of the pigment. Johann Ludwig Wilhelm Thudichum, in 1868–1869, after stereoscopic spectral examination, applied the term 'luteine' (lutein) to this class of yellow crystallizable substances found in animals and plants. Richard Martin Willstätter, who gained the Nobel Prize in Chemistry in 1915, mainly for his work on chlorophyll, assigned the composition of C40H56, distinguishing it from the similar but oxygenated xanthophyll, C40H56O2. With Heinrich Escher, in 1910, lycopene was isolated from tomatoes and shown to be an isomer of carotene. Later work by Escher also differentiated the 'luteal' pigments in egg yolk from that of the carotenes in cow corpus luteum.

Dietary sources
The following foods contain carotenes in notable amounts:

 * carrots
 * wolfberries (goji)
 * cantaloupe
 * mangoes
 * red bell pepper
 * papaya
 * spinach
 * kale
 * sweet potato
 * tomato
 * dandelion greens
 * broccoli
 * collard greens
 * winter squash
 * pumpkin
 * cassava

Absorption from these foods is enhanced if eaten with fats, as carotenes are fat soluble, and if the food is cooked for a few minutes until the plant cell wall splits and the color is released into any liquid. 12 μg of dietary β-carotene supplies the equivalent of 1 μg of retinol, and 24 μg of α-carotene or β-cryptoxanthin provides the equivalent of 1 μg of retinol.

Forms of carotene
The two primary isomers of carotene, α-carotene and β-carotene, differ in the position of a double bond (and thus a hydrogen) in the cyclic group at one end (the right end in the diagram at right).

β-Carotene is the more common form and can be found in yellow, orange, and green leafy fruits and vegetables. As a rule of thumb, the greater the intensity of the orange colour of the fruit or vegetable, the more β-carotene it contains.

Carotene protects plant cells against the destructive effects of ultraviolet light so β-carotene is an antioxidant.

β-Carotene and cancer
An article on the American Cancer Society says that The Cancer Research Campaign has called for warning labels on β-carotene supplements to caution smokers that such supplements may increase the risk of lung cancer.

The New England Journal of Medicine published an article in 1994 about a trial which examined the relationship between daily supplementation of β-carotene and vitamin E (α-tocopherol) and the incidence of lung cancer. The study was done using supplements and researchers were aware of the epidemiological correlation between carotenoid-rich fruits and vegetables and lower lung cancer rates. The research concluded that no reduction in lung cancer was found in the participants using these supplements, and furthermore, these supplements may, in fact, have harmful effects.

The Journal of the National Cancer Institute and The New England Journal of Medicine published articles in 1996 about a trial with a goal to determine if vitamin A (in the form of retinyl palmitate) and β-carotene (at about 30 mg/day, which is 10 times the Reference Daily Intake) supplements had any beneficial effects to prevent cancer. The results indicated an increased risk of lung and prostate cancers for the participants who consumed the β-carotene supplement and who had lung irritation from smoking or asbestos exposure, causing the trial to be stopped early.

A review of all randomized controlled trials in the scientific literature by the Cochrane Collaboration published in JAMA in 2007 found that synthetic β-carotene increased mortality by 1–8% (Relative Risk 1.05, 95% confidence interval 1.01–1.08). However, this meta-analysis included two large studies of smokers, so it is not clear that the results apply to the general population. The review only studied the influence of synthetic antioxidants and the results should not be translated to potential effects of fruits and vegetables.

β-Carotene and photosensitivity
Oral β-carotene is prescribed to people suffering from erythropoietic protoporphyria. It provides them some relief from photosensitivity.

Carotenemia
Carotenemia or hypercarotenemia is excess carotene, but unlike excess vitamin A, carotene is non-toxic. Although hypercarotenemia is not particularly dangerous, it can lead to an oranging of the skin (carotenodermia), but not the conjunctiva of eyes (thus easily distinguishing it visually from jaundice). It is most commonly associated with consumption of an abundance of carrots, but it also can be a medical sign of more dangerous conditions.

Production
Carotenes are produced in a general manner for other terpenoids and terpenes, i.e. by coupling, cyclization, and oxygenation reactions of isoprene derivatives. Lycopene is the key precursor to carotenoids. It is formed by coupling of geranylgeranyl pyrophosphate and geranyllinally pyrophosphate.

Most of the world's synthetic supply of carotene comes from a manufacturing complex located in Freeport, Texas and owned by DSM. The other major supplier BASF also uses a chemical process to produce β-carotene. Together these suppliers account for about 85% of the β-carotene on the market. In Spain Vitatene produces natural β-carotene from fungus Blakeslea trispora, as does DSM but at much lower amount when compared to its synthetic β-carotene operation. In Australia, organic β-carotene is produced by Aquacarotene Limited from dried marine algae Dunaliella salina grown in harvesting ponds situated in Karratha, Western Australia. BASF Australia is also producing β-carotene from microalgae grown in two sites in Australia that are the world's largest algae farms. In Portugal, the industrial biotechnology company Biotrend is producing natural all-trans-β-carotene from a non-genetically modified bacteria of the genus Sphingomonas isolated from soil.

Carotenes are also found in palm oil, corn, and in the milk of dairy cows, causing cow's milk to be light yellow, depending on the feed of the cattle, and the amount of fat in the milk (high-fat milks, such as those produced by Guernsey cows, tend to be yellower because their fat content causes them to contain more carotene).

Carotenes are also found in some species of termites, where they apparently have been picked up from the diet of the insects.

Synthesis
There are currently two commonly used methods of total synthesis of β-carotene. The first was developed by BASF and is based on the Wittig reaction with Wittig himself as patent holder:

 * Wittig-9.svg

The second is a Grignard reaction, elaborated by Hoffman-La Roche from the original synthesis of Inhoffen et al. They are both symmetrical; the BASF synthesis is C20 + C20, and the Hoffman-La Roche synthesis is C19 + C2 + C19.

Nomenclature
Carotenes are carotenoids containing no oxygen. Carotenoids containing some oxygen are known as xanthophylls.

The two ends of the β-carotene molecule are structurally identical, and are called β-rings. Specifically, the group of nine carbon atoms at each end form a β-ring.

The α-carotene molecule has a β-ring at one end; the other end is called an ε-ring. There is no such thing as an "α-ring".

These and similar names for the ends of the carotenoid molecules form the basis of a systematic naming scheme, according to which:
 * α-carotene is β,ε-carotene;
 * β-carotene is β,β-carotene;
 * γ-carotene (with one β ring and one uncyclized end that is labelled psi) is β,ψ-carotene;
 * δ-carotene (with one ε ring and one uncyclized end) is ε,ψ-carotene;
 * ε-carotene is ε,ε-carotene
 * lycopene is ψ,ψ-carotene

ζ-Carotene is the biosynthetic precursor of neurosporene, which is the precursor of lycopene, which, in turn, is the precursor of the carotenes α through ε.

Food additive
Carotene is used to colour products such as juice, cakes, desserts, butter and margarine. It is approved for use as a food additive in the EU (listed as additive E160a) Australia and New Zealand (listed as 160a) and the US.

title: Carotene


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This article is or was the subject of a Wiki Education Foundation-supported course assignment. Further details are available on the course page. Student editor(s): Mzh0015. Peer reviewers: Mzh0015.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 17:03, 16 January 2022 (UTC)

Article's quality
Does it describe Eukaryotic cells or all cells ? Do all cells folow this cycle or are there some exceptions ? -- Taw

 * I think this is specific only to eucaryotes, but among these, the mechanism is fairly conserved from yeast to man. AttishOculus 22:19, 11 Jun 2005 (UTC)

Is there a reason to have this article separate from Cell division and Mitosis - Marshman 05:46, 30 Sep 2003 (UTC)

 * Yes. Mitosis is only one small part of the cell cycle. There is more than enough information about mitosis to justify its having its own entry, but it should not be combined with cell cycle. ~mdash; Brim 17:38, Nov 27, 2004 (UTC)

I think this topic would deserve some additional, more detailed information. (exeact transitions, checkpoints, cyclins, CDK's and CKI's in detail etc.) I would be glad to add some more information, regarding the importance of the subject (in cancer research, for example), but as I am only a I could use no other source of knowledge but my textbooks, so I would be happy to have an expert look through my work every once in a while.

Additionally, I fear that stacking up the article with scientific info would make the whole article frightening and overwhelming for non-professionals. What would you recommend in order to avoid that? Would having separate sections in the article after the current one as an introduction be sufficient, or would it be better to add a new article "Cell cycle in detail", or just have a number of new pages linked into the main page (eg. "Replication initiation mechanisms")? What would be the general Wikipedia practice in such cases? AttishOculus 22:19, 11 Jun 2005 (UTC)

This article lacks so much info...i mean a lot. I came here looking for help on the topic--because i just couldn't understand some of it, and it wasn't here. All of the stages require info of the cell cycle. The Mitosis part deserves its own part. The cycle's checking system needs its own part. This is one bad article. I'll try to fix it in a day or two after my test. :) Nominaladversary 01:54, 31 March 2006 (UTC)
 * The mitosis part has its own part at mitosis. I'd bet my boots check points will also direct you to the cycle's checking system too. Aaadddaaammm 07:10, 19 October 2006 (UTC)

Image of cell cycle regulation is wrong. Cyclin E-CDK2 complex regulates G1/S checkpoint, not G2/M; and vice versa for Cyclin A-CDK2 complex. A correct image is accessible here: http://en.wikipedia.org/wiki/File:Regulation_of_cell_cycle.png --Iflex (talk) 06:49, 10 September 2010 (UTC)

No description of basic process of cell division
There has to be a section dvoted to description of all phases during mitosis (and variations during a meiosis). The article seems to dwell heavily upon recent advances in molecular biology. These advances have to be placed in perspective with the general biology of the cell cycle Nattu 20:21, 16 June 2006 (UTC)
 * This article is a recent retooling of a rather poor, stubby original. Currently mitosis and meiosis have their own articles, which are in a much better state than this one was; the phases of mitosis also have their own articles. There's an emphasis on molecular biology in the current article because I wrote it :) Feel free to add more general information, as I think in time this article should evolve to be a proper header for Category:Cell cycle.
 * Yes, the mol bio part is good and we can shape it further. For now, emphasis must be on cell cycle basics and I will contribute my bit to it. Nattu 19:19, 23 June 2006 (UTC)

Cell Cycle Regulation Diagram Removed
The current illustration of the cell cycle should be removed or replaced in my opinion. It would almost have been ok if all the phases seemed to have equal duration. But in this illustration S phase is actually smaller than the G2 phase! - HungryHippo 19. july 2006
 * You're right, it's not really very good, but I do think it's better than nothing (especially given the explanation of its deficiencies in the caption). I've posted a in the hopes of attracting a good diagram creator, which I am not. Opabinia regalis 02:07, 20 July 2006 (UTC)

The second diagram on this page is horrificly inaccurate. How it can center around CDK2 when it has been shown that this is redundant to CDK1?

Berthet, C., E. Aleem, V. Coppola, L. Tessarollo, and P. Kaldis. 2003. Cdk2 knockout mice are viable. Curr. Biol. 13:1775–1785.

The Journal of Cell Biology, Vol. 178, No. 2, July 16, 2007 257–268

Please consider revision of this image! —Preceding unsigned comment added by 129.31.120.113 (talk) 11:34, 8 July 2009 (UTC)

 * I removed the diagram in question because of several patent falsehoods in addition to those already mentioned: i.e., Cyclin-B complexes with CDK1 to resolve the G2-to-M checkpoint. In the diagram, CyclinE/CDK2 is depicted in that role, which is not the case. The Cyclin-E/CDK2 complex actually resolves the G1-to-S checkpoint, which leads to another inaccuracy in the diagram: Cyclin-A/CDK2 do not resolve G1-to-S, as shown, but rather the S-to-G2 checkpoint. Because of this, I removed the diagram from the page, as it is too misleading to be useful.  Link to removed file: http://en.wikipedia.org/wiki/File:Regulation_of_the_cell_cycle.svg  —Preceding unsigned comment added 11:24, 18 May 2011 (UTC)

About diploid, haploid and monoploid
"In this quantity of DNA within the cell has increased to 4c, but the cell is still considered diploid." Finally i got the information.

embryology
Does anyone happen to know any embryologists? I think Embryology really needs a lot of expert attention. would sympathtic editors consider a positive vote here? Slrubenstein  |  Talk 19:05, 28 August 2006 (UTC)

Mitosis vs. M phase
As far as I know M phase=Mitosis+Cytokinesis, but there is no article on M phase, only on Mitosis, and in the picture:, I think, M phase is denoted by letter "M" and not Mitosis, as there are four phases: G1, S, G2 and M (+G0). Should the text below the picture be changed? Andrius 14:49, 29 October 2006 (UTC)

About the diagram
I can make a fairly good diagram, but I am not an exepert on cellulear procesess, so e-mail me with even a napkin drawing of the correct process and I'll "pimp it out". thanks

Yupi666 20:15, 14 June 2007 (UTC)

Copyedit and minor expansion
I have done some minor expansion and copy-editing and fixed some formatting issues. I will be adding some references in the coming one or two days. Please comment here if there are any errors or omissions. Also, I think it would be better if we do away with the Observation and Research Groups sections. Also, Regulation of cell cycle can be greatly expanded. Or can be made into a totally separate article. Any comments? - Two  Oars  10:46, 1 August 2007 (UTC)

The template
As an aside, how about adding links to the checkpoints from Cell cycle? Please comment at Template talk:Cell cycle. Thanks. - Two  Oars  18:20, 3 August 2007 (UTC)
 * Never mind. Has been taken care of by Arcadian. - Two  Oars  17:07, 4 August 2007 (UTC)

 * Nobody should be an aside in Wikipedia - feel as free to edit as anybody! Mikael Häggström 16:30, 5 August 2007 (UTC)

Another problem with the diagram
The Yellow "M" should not refer to Metaphase but to mitosis again. The counterpart of interphase is not the metaphase but the mitosis which include prophase, metaphase, anaphase and telophase. —Preceding unsigned comment added by Vardos (talk • contribs)
 * You are right. I changed it. I don't know how we missed it all this while, that too after a monthly collaboration. :P - Two  Oars   (Rev)  16:03, 7 October 2007 (UTC)

Why only eukaryotes?
The term Cell Cycle can apply to both prokaryotes and eukarotes, but the article focuses entirely on eukaryotes. In my opinion the article can be strengthened with an additional prokaryote section....or at the minimum, include some sort of reference to prokaryotes. --Naturespace (talk) 04:56, 5 December 2008 (UTC)

Quality
i would just like to note that my grade 9 science textbook has better descriptions on what actually happens in cell division and if i remember correctly there are alot more phases than the 4 mentioned.... Walkerm930 (talk) 19:40, 27 March 2009 (UTC)

 * I think the confusion here is that you may have been looking for the mitosis or cell division article(s) and not cell cycle. The treatment of the cell cycle in high school biology books, if it is mentioned at all, is very brief. Mitosis in contrast is treated in some depth.  The mitosis stage of the cell cycle involves the physical separation of the duplicated chromosomes during cell division and is divided into prophase/prometaphase/metaphase/anaphase/telophase substages (see the diagram below the Mitosis section).  The cell cycle, in addition to the mitosis step, involves growth of the cell and molecular replication of DNA. Cheers. Boghog2 (talk) 07:06, 28 March 2009 (UTC)

 * I have just added the following to the top of this article:

 * I hope this reduces the confusion. Boghog2 (talk) 20:35, 7 April 2009 (UTC)
 * Or even more to the point:
 * Boghog2 (talk) 05:10, 8 April 2009 (UTC)

cell cycle
is a function of life and how that it wordks —Preceding unsigned comment added by 170.211.230.126 (talk) 14:20, 1 October 2009 (UTC)

quinescent phase
I've always hated the term "resting phase." The cell is performing all of it's functions except those related to dividing, should we really refer to it as the "resting phase?" —Preceding unsigned comment added by 64.221.247.194 (talk) 12:15, 21 October 2010 (UTC) Umm Like I Didnt Understand At First But Now I Totaly Get It (:! — Preceding unsigned comment added by 66.87.0.231 (talk) 00:50, 30 August 2011 (UTC)

Diagram?
I altered one of the cell cycle diagrams to better reflect the duration of each phase of the cycle (reference) but I don’t know much about editing (or if the duration of mitosis was exaggerated for a good reason for that matter). Anyway… here it is. --Histidine (talk) 11:16, 22 January 2011 (UTC)

 * Your modifications to the diagram look reasonable and I would support replacing the original with this modified version. There is one minor problem however.  The original is in the preferred svg format while the modified version is png.  Would it be possible to produce a modified version in svg format? Boghog (talk) 13:17, 22 January 2011 (UTC)

 * I just tried to upload an svg version and, long story short, it did not go well the first two times (I am sorry about making a mess). It is still rendering differently then it should be, but this is the best I could do. Maybe I'll learn how to make a better one later. --Histidine (talk) 09:10, 23 January 2011 (UTC)

 * Thanks. Your svg version looks OK to me.  The font is not as quite as clean, on the other hand I like the larger font size which makes the thumb nail depiction more legible.  I think it is good enough replace the current version in the article.  Cheers.  Boghog (talk) 11:21, 23 January 2011 (UTC)

 * Yes, the font is one of the things that came out differently once I uploaded it. I read it is a bug with using Inkscape, so I might try to sort that out at some point. --Histidine (talk) 20:27, 23 January 2011 (UTC)

 * I think I figured out all my bugs with uploading. If no one opposes I will replace the one in the article. --Histidine (talk) 02:06, 25 January 2011 (UTC)

 * Thanks for fixing the remaining bugs. The graphic looks perfect.  Boghog (talk) 06:04, 25 January 2011 (UTC)

Overall quality
The overall quality of the article is still lacking significant detail and in depth information. Different phases seem to be short and may need more information, for example S phase does not really elaborate much on its purpose. — Preceding unsigned comment added by Nvarade (talk • contribs) 02:32, 4 February 2014 (UTC)

Assessment comment
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title: Talk:Cell cycle


text:
Cyclic adenosine monophosphate

Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger, or cellular signal occurring within cells, that is important in many biological processes. cAMP is a derivative of adenosine triphosphate (ATP) and used for intracellular signal transduction in many different organisms, conveying the cAMP-dependent pathway.

History
Earl Sutherland of Vanderbilt University won a Nobel Prize in Physiology or Medicine in 1971 "for his discoveries concerning the mechanisms of the action of hormones", especially epinephrine, via second messengers (such as cyclic adenosine monophosphate, cyclic AMP).

Synthesis
Cyclic AMP is synthesized from ATP by adenylate cyclase located on the inner side of the plasma membrane and anchored at various locations in the interior of the cell. Adenylate cyclase is activated by a range of signaling molecules through the activation of adenylate cyclase stimulatory G (Gs)-protein-coupled receptors. Adenylate cyclase is inhibited by agonists of adenylate cyclase inhibitory G (Gi)-protein-coupled receptors. Liver adenylate cyclase responds more strongly to glucagon, and muscle adenylate cyclase responds more strongly to adrenaline.

cAMP decomposition into AMP is catalyzed by the enzyme phosphodiesterase.

Functions
cAMP is a second messenger, used for intracellular signal transduction, such as transferring into cells the effects of hormones like glucagon and adrenaline, which cannot pass through the plasma membrane. It is also involved in the activation of protein kinases. In addition, cAMP binds to and regulates the function of ion channels such as the HCN channels and a few other cyclic nucleotide-binding proteins such as Epac1 and RAPGEF2.

Role in eukaryotic cells
cAMP is associated with kinases function in several biochemical processes, including the regulation of glycogen, sugar, and lipid metabolism.

In eukaryotes, cyclic AMP works by activating protein kinase A (PKA, or cAMP-dependent protein kinase). PKA is normally inactive as a tetrameric holoenzyme, consisting of two catalytic and two regulatory units (C2R2), with the regulatory units blocking the catalytic centers of the catalytic units.

Cyclic AMP binds to specific locations on the regulatory units of the protein kinase, and causes dissociation between the regulatory and catalytic subunits, thus enabling those catalytic units to phosphorylate substrate proteins.

The active subunits catalyze the transfer of phosphate from ATP to specific serine or threonine residues of protein substrates. The phosphorylated proteins may act directly on the cell's ion channels, or may become activated or inhibited enzymes. Protein kinase A can also phosphorylate specific proteins that bind to promoter regions of DNA, causing increases in transcription. Not all protein kinases respond to cAMP. Several classes of protein kinases, including protein kinase C, are not cAMP-dependent.

Further effects mainly depend on cAMP-dependent protein kinase, which vary based on the type of cell.

Still, there are some minor PKA-independent functions of cAMP, e.g., activation of calcium channels, providing a minor pathway by which growth hormone-releasing hormone causes a release of growth hormone.

However, the view that the majority of the effects of cAMP are controlled by PKA is an outdated one. In 1998 a family of cAMP-sensitive proteins with guanine nucleotide exchange factor (GEF) activity was discovered. These are termed Exchange proteins activated by cAMP (Epac) and the family comprises Epac1 and Epac2. The mechanism of activation is similar to that of PKA: the GEF domain is usually masked by the N-terminal region containing the cAMP binding domain. When cAMP binds, the domain dissociates and exposes the now-active GEF domain, allowing Epac to activate small Ras-like GTPase proteins, such as Rap1.

Additional role of secreted cAMP in social amoebae
In the species Dictyostelium discoideum, cAMP acts outside the cell as a secreted signal. The chemotactic aggregation of cells is organized by periodic waves of cAMP that propagate between cells over distances as large as several centimetres. The waves are the result of a regulated production and secretion of extracellular cAMP and a spontaneous biological oscillator that initiates the waves at centers of territories.

Role in bacteria
In bacteria, the level of cAMP varies depending on the medium used for growth. In particular, cAMP is low when glucose is the carbon source. This occurs through inhibition of the cAMP-producing enzyme, adenylate cyclase, as a side-effect of glucose transport into the cell. The transcription factor cAMP receptor protein (CRP) also called CAP (catabolite gene activator protein) forms a complex with cAMP and thereby is activated to bind to DNA. CRP-cAMP increases expression of a large number of genes, including some encoding enzymes that can supply energy independent of glucose.

cAMP, for example, is involved in the positive regulation of the lac operon. In an environment with a low glucose concentration, cAMP accumulates and binds to the allosteric site on CRP (cAMP receptor protein), a transcription activator protein. The protein assumes its active shape and binds to a specific site upstream of the lac promoter, making it easier for RNA polymerase to bind to the adjacent promoter to start transcription of the lac operon, increasing the rate of lac operon transcription. With a high glucose concentration, the cAMP concentration decreases, and the CRP disengages from the lac operon.

Pathology
Since cyclic AMP is a second messenger and plays vital role in cell signalling, it has been implicated in various disorders but not restricted to the roles given below:

Role in human carcinoma
Some research has suggested that a deregulation of cAMP pathways and an aberrant activation of cAMP-controlled genes is linked to the growth of some cancers.

Role in prefrontal cortex disorders
Recent research suggests that cAMP affects the function of higher-order thinking in the prefrontal cortex through its regulation of ion channels called hyperpolarization-activated cyclic nucleotide-gated channels (HCN). When cAMP stimulates the HCN, the channels open, This research, especially the cognitive deficits in age-related illnesses and ADHD, is of interest to researchers studying the brain.

cAMP is involved in activation of trigeminocervical system leading to neurogenic inflammation and causing migraine.

Role in infectious disease agents' pathogenesis
Disrupted functioning of cAMP has been noted as one of the mechanisms of several bacterial exotoxins.

They can be subgrouped into two distinct categories:

 * Toxins that interfere with enzymes ADP-ribosyl-transferases, and
 * invasive adenylate cyclases.

ADP-ribosyl-transferases related toxins

 * Cholera toxin is an AB toxin that has five B subunints and one A subunit. The toxin acts by the following mechanism: First, the B subunit ring of the cholera toxin binds to GM1 gangliosides on the surface of target cells. If a cell lacks GM1 the toxin most likely binds to other types of glycans, such as Lewis Y and Lewis X, attached to proteins instead of lipids.

Uses
Forskolin is commonly used as a tool in biochemistry to raise levels of cAMP in the study and research of cell physiology.

title: Cyclic adenosine monophosphate