document_title: Bonnie and Clyde (film)

question_text: who played bonnie in the movie bonnie and clyde

text: Bonnie and Clyde (film)

text: Plot[edit]

text: In the middle of the Great Depression, Clyde Barrow (Warren Beatty) and Bonnie Parker (Faye Dunaway) meet when Clyde tries to steal Bonnie's mother's car. Bonnie, who is bored by her job as a waitress, is intrigued by Clyde, and decides to take up with him and become his partner in crime. They pull off some holdups, but their amateur efforts, while exciting, are not very lucrative.

text: The duo's crime spree shifts into high gear once they hook up with a dim-witted gas station attendant, C.W. Moss (Michael J. Pollard), then with Clyde's older brother Buck (Gene Hackman) and his wife, Blanche (Estelle Parsons), a preacher's daughter. The women dislike each other on first sight, and their feud only escalates from there: shrill Blanche has nothing but disdain for Bonnie, Clyde and C.W., while gun-moll Bonnie sees Blanche's flighty presence as a constant danger to the gang's well-being.

text: Bonnie and Clyde turn from pulling small-time heists to robbing banks. Their exploits also become more violent. When C.W. botches a bank robbery by parallel parking the getaway car, Clyde shoots the bank manager in the face after he jumps onto the slow-moving car's running board. The gang is pursued by law enforcement, including Texas Ranger Frank Hamer (Denver Pyle), whom they capture and humiliate before setting him free. A raid later catches the outlaws off guard, mortally wounding Buck with a gruesome shot to his head and injuring Blanche. Bonnie, Clyde and C.W. barely escape with their lives. With Blanche sightless and in police custody, Hamer tricks her into revealing C.W.'s name, who was up until now still only an "unidentified suspect."

text: Hamer locates Bonnie, Clyde and C.W. hiding at the house of C.W.'s father Ivan Moss (Dub Taylor), who thinks the couple—and an ornate tattoo—have corrupted his son. The elder Moss strikes a bargain with Hamer: in exchange for leniency for the boy, he helps set a trap for the outlaws. When Bonnie and Clyde stop on the side of the road to help Mr. Moss fix a flat tire, the police in the bushes open fire and riddle them with bullets. Hamer and his posse then come out of hiding, looking pensively at the couple's bodies.

text: Cast[edit]

text:
Warren Beatty as Clyde Barrow
Faye Dunaway as Bonnie Parker
Michael J. Pollard as C.W. Moss
Gene Hackman as Buck Barrow
Estelle Parsons as Blanche Barrow
Denver Pyle as Frank Hamer
Dub Taylor as Ivan Moss
Gene Wilder as Eugene Grizzard
Evans Evans as Velma Davis
Mabel Cavitt as Bonnie's mother (uncredited)

text: Cast notes[edit]

text: Actor Gene Wilder portrayed Eugene Grizzard, one of Bonnie and Clyde's hostages. His girlfriend Velma Davis was played by Evans Evans, who was the wife of film director John Frankenheimer.

text: The family gathering scene was filmed in Red Oak, Texas. Several local residents gathered to watch the film being shot. When the filmmakers noticed Mabel Cavitt, a local school teacher, among the people gathered, she was cast as Bonnie Parker's mother.[7][8] Cavitt delivers key lines in the film that represent a turning point in the plot. When Clyde promises to give up crime, marry Bonnie and move back near her mother, Mrs. Parker rebuffs Clyde by saying "You best keep runnin' Clyde Barrow. And you know it." She then hugs Bonnie and says "Bye, baby." From this point in the film, the Barrow gang begins its demise.

text: Production and style[edit]

text: The film was intended as a romantic and comic version of the violent gangster films of the 1930s, updated with modern filmmaking techniques.[9] Arthur Penn portrayed some of the violent scenes with a comic tone, sometimes reminiscent of Keystone Kops-style slapstick films, then shifted disconcertingly into horrific and graphic violence.[10] The film was strongly influenced by the French New Wave directors, both in its rapid shifts of tone, and in its choppy editing, which is particularly noticeable in the film's closing sequence.[10]

text: The first handling of the script was in the early 1960s. Very influenced by the French New Wave writers and in a state not yet completed, it was first sent by its writers David Newman and Robert Benton to Arthur Penn. He was already engaged in the first decisions of production for the 1966 film The Chase and could not further involve himself at that point. The writers then sent to François Truffaut, renowned director of the New Wave movement, who made contributions to the script. He passed on the project and went on to make Fahrenheit 451.[11] At Truffaut's suggestion, the writers, much excited (the film's then-producers less so), approached Jean-Luc Godard. Some sources claim Godard didn't trust Hollywood and refused; Robert Benton claimed that Godard wanted to shoot the film in New Jersey in January during the winter and took offense when would-be producer Norah Wright objected that that was unreasonable considering the story took place in Texas with its year-round warm environment.[12] Her partner Elinor Jones[13] claimed they did not believe Godard was right for the project in the first place. Godard's retort: « Je vous parle de cinéma, vous me parlez de météo. Au revoir. » ("I'm talking cinema and you're talking weather. Goodbye.")[14] After the 1968 Academy Awards, Godard sent Benton and Newman a cable that read, "Now, let's make it all over again!"[15]

text: Soon after the failed negotiations for production, Warren Beatty was visiting Paris and learned through Truffaut of the project and its perambulations. On returning to Hollywood, Beatty requested the script and bought the rights. A meeting with Godard was not productive. Beatty then changed compass and convinced the writers that while the script at first reading was very much of the French New Wave style, an American director was necessary for the subject.[16]

text: Beatty offered the position to George Stevens, William Wyler, Karel Reisz, John Schlesinger, Brian G. Hutton, and Sydney Pollack, all of whom turned down the opportunity. Arthur Penn actually turned down the director's position again further times before Beatty finally convinced him to helm the film.[17]

text: When Warren Beatty was on board as producer only, his sister Shirley MacLaine was a strong possibility to play Bonnie, but when Beatty decided to play Clyde, obviously a different actress was needed. Those considered for the role were Jane Fonda, Tuesday Weld, Ann-Margret, Leslie Caron, Carol Lynley and Sue Lyon. Cher auditioned for the part, while Warren Beatty begged Natalie Wood to play the role. Wood declined the role to concentrate more on her therapy at the time, and acknowledged that working with Beatty before was "difficult." Faye Dunaway stated that she won the part "by the skin of her teeth!"[citation needed]

text: The film is forthright in its handling of sexuality, but that theme was toned down from its conception. Originally, Benton and Newman wrote Clyde as bisexual and he and Bonnie were to have a three-way sexual relationship with their male getaway driver. However, Arthur Penn persuaded the writers that since the relationship's emotional complexity was underwritten, it dissipated the passion of the title characters and it would harm the audience's sympathy for the characters who would write them off as sexual deviants because they were criminals. Others claimed that Beatty was not willing to have his character display that kind of sexuality and that the Production Code would never have allowed such content in the first place.[18] Instead, Clyde is portrayed as unambiguously heterosexual, if impotent. When Clyde brandishes his gun to display his manhood, Bonnie suggestively strokes the phallic symbol. Like the 1950 film Gun Crazy, Bonnie and Clyde portrays crime as alluring and intertwined with sex. Because Clyde is impotent, his attempts to physically woo Bonnie are frustrating and anti-climactic.

text: Bonnie and Clyde was one of the first films to feature extensive use of squibs – small explosive charges, often mounted with bags of stage blood, that are detonated inside an actor's clothes to simulate bullet hits. Released in an era where shootings were generally depicted as bloodless and painless, the Bonnie and Clyde death scene was one of the first in mainstream American cinema to be depicted with graphic realism.[citation needed]

text: Beatty had originally wanted the film to be shot in black and white, but Warner Bros. rejected this idea. As it stood, much of the senior management of the studio was hostile to this film project, especially Jack L. Warner who considered the subject-matter an unwanted throwback to Warner Bros.' early period when gangster films were common product.[19] In addition, Warner was already annoyed at Beatty who refused to star in the film, PT 109 at his behest and was insolent enough to defy his favorite gesture of authority of showing the studio water tower with the WB logo on it by responding "Well, it's got your name, but it's got my initials."[20] In addition, Warner complained about the film's extensive location shooting in Texas which exceeded its production schedule and budget, until he ordered the crew back to the studio backlot, where it was planned to be anyway for final process shots.[21]

text: At first, Warner Bros. did not promote Bonnie and Clyde for general release, but instead mounted only limited regional releases that seemed to confirm its misgivings about the film's lack of commercial appeal, despite the fact the film was doing excellent sustained business in select urban theatres.[22] In fact, while Jack Warner was selling the studio to Seven Arts Productions, he would have had the film dumped but for the fact that Israel, of which Warner was a major supporter, had scored a triumphant victory in the Six Day War, and he was in too defiant a mood to sell any of his studio's films.[23] Meanwhile, Warren Beatty, Bonnie and Clyde's producer and star, complained to Warner Bros. that if the company was willing to go to so much trouble for Reflections in a Golden Eye (they had changed the coloration scheme at considerable expense), their neglect of his film, which was getting excellent press, suggested a conflict of interest; he threatened to sue the company. Warner Bros. gave Beatty's film a general release. Much to Warner Bros.' management surprise, the film eventually became a major box office success.[24]

text: Music[edit]

text: The instrumental banjo piece "Foggy Mountain Breakdown" by Flatt and Scruggs was introduced to a worldwide audience as a result of its frequent use in the movie. Its use is strictly anachronistic as the bluegrass-style of music dates from the mid-1940s rather than the 1930s, but the functionally similar Old-time music genre was long established and widely recorded at the period in which the film is set.[citation needed] Long out of print in vinyl and cassette formats, the film soundtrack album was finally released on CD in 2009.[25]

text: Historical accuracy[edit]

text: The film considerably simplifies the lives of Bonnie and Clyde, which included other gang members, repeated jailings, other murders and a horrific auto accident that left Parker burned and a near-invalid.

text: The Gene Wilder–Evans Evans sequence is based on the kidnappings of the undertaker H. D. Darby and his acquaintance Sophia Stone, near Ruston, Louisiana on the late afternoon of April 27, 1933 by the Barrow gang, who had stolen their car.[26]

text: The film strays furthest from fact in its portrayal of the Texas Ranger Frank Hamer as a vengeful bungler who had been captured, humiliated, and released by Bonnie and Clyde. In real life, Hamer was already a legendary and decorated Texas Ranger when he was coaxed out of semi-retirement to hunt down the duo; indeed he had never seen them until the moment he and his posse ambushed them near Gibsland, Louisiana on May 23, 1934.[27] In 1968, Hamer's widow and son sued the movie producers for defamation of character over his portrayal and were awarded an out-of-court settlement in 1971.[28]

text: The couple's notoriety in 1933 came from photos found by police as undeveloped film in a hastily abandoned hideout in Joplin, Missouri. In one, Bonnie holds a gun in her hand and a cigar between her teeth. Its publication nationwide typed her as a dramatic gun moll. The film portrays the taking of this playful photo. It implies the gang sent photos—and poetry—to the press, but this is untrue. The police found most of the gang's items in the Joplin cache. Bonnie's final poem, read aloud by her in the movie, was publicized only posthumously by her mother.[29]

text: The only two members of the Barrow Gang who were alive at the time of the film's release were Blanche Barrow and W. D. Jones. While Blanche Barrow approved the depiction of her in the original version of the script, she objected to the later re-writes. At the film's release, she complained loudly about Estelle Parsons's portrayal of her, saying, "That film made me look like a screaming horse's ass!"[30]

text: Reception[edit]

text: The film was controversial on its original release for its supposed glorification of murderers, and for its level of graphic violence, which was unprecedented at the time. Bosley Crowther of The New York Times was so appalled that he began to campaign against the increasing brutality of American films.[31] Dave Kaufman of Variety criticized the film for uneven direction and for portraying Bonnie and Clyde as bumbling fools.[32] Joe Morgenstern for Newsweek initially panned the film as a "squalid shoot-'em-up for the moron trade." After seeing the film a second time and noticing the enthusiastic audience, he wrote a second article saying he had misjudged it and praised the film. Warner Bros. took advantage of this, marketing the film as having made a major critic change his mind about its virtues.[33]

text: Roger Ebert gave Bonnie and Clyde a largely positive review, giving it four stars out of four. He called the film "a milestone in the history of American movies, a work of truth and brilliance." More than 30 years later, he added the film to his The Great Movies list. Film critics Dave Kehr and James Berardinelli have also praised the film in the years since.

text: The fierce debate about the film is discussed at length in For the Love of Movies: The Story of American Film Criticism. This 2009 documentary film chronicles what occurred as a result: The New York Times fired Bosley Crowther because his negative review seemed so out of touch with the public, and Pauline Kael, who wrote a lengthy freelance essay in The New Yorker in praise of the film, became the magazine's new staff-critic.

text: It performed well at the box office, and by year's end had grossed $23,000,000 in US theatrical rentals, becoming the studio's second highest-grossing film of all time, right behind My Fair Lady.[34] Listal lists it as one of the top five grossing films of 1967 with $50,700,000 in US sales, and $70,000,000 worldwide.[35]

text: Although many believe the film's groundbreaking portrayal of violence adds to the film's artistic merit, Bonnie and Clyde is still sometimes criticized for opening the floodgates for violence in cinema.[36] It currently holds a 90% "Certified Fresh" rating on Rotten Tomatoes,[37] with 45/50 reviews positive.

text: Accolades[edit]

text: Estelle Parsons won an Academy Award for Best Supporting Actress for her portrayal of Blanche Barrow, and Burnett Guffey won an Academy Award for Best Cinematography.

text: The film was also nominated for:

text:
Best Picture – Warren Beatty
Best Director – Arthur Penn
Best Writing (Screenplay Written Directly for the Screen) – David Newman and Robert Benton
Best Actor in a Leading Role – Warren Beatty
Best Actress in a Leading Role – Faye Dunaway
Best Actor in a Supporting Role – Gene Hackman
Best Actor in a Supporting Role – Michael J. Pollard
Best Costume Design – Theadora Van Runkle

text: In 1992, Bonnie and Clyde was selected for preservation in the United States National Film Registry by the Library of Congress as being "culturally, historically, or aesthetically significant."

text:
1998 – AFI's 100 Years...100 Movies – #27
2001 – AFI's 100 Years...100 Thrills – #13
2002 – AFI's 100 Years...100 Passions – #65
2003 – AFI's 100 Years...100 Heroes and Villains

Clyde Barrow & Bonnie Parker – #32 Villains

2005 – AFI's 100 Years...100 Movie Quotes – #41

"We rob banks." – #41

2007 – AFI's 100 Years...100 Movies (10th Anniversary Edition) – #42
2008 – AFI's 10 Top 10 – #5 Gangster Film[38]

text: In 2012, the Motion Picture Editors Guild listed the film as the fifth best edited film of all time based on a survey of its membership.[39]

text: Influence[edit]

text: Forty years after its premiere, Bonnie and Clyde has been cited as a major influence for such disparate films as The Wild Bunch, The Godfather, The Departed,[40] and Natural Born Killers.[41]

text: In popular culture[edit]

text: The "Storage Jars" skit of episode 33 of Monty Python's Flying Circus features a brief still shot of Warren Beatty as Clyde Barrow firing a Thompson submachine gun as he escapes from the Red Crown Tourist Court. [42]


document_title: Electron transport chain

question_text: where do krebs (step 2) and the etc (step 3) occur

question_tokens: where do krebs ( step 2 ) and the etc ( step 3 ) occur

root

text: Electron transport chain

text: Background[edit]

text: The electron transport chain consists of a spatially separated series of redox reactions in which electrons are transferred from a donor molecule to an acceptor molecule. The underlying force driving these reactions is the Gibbs free energy of the reactants and products. The Gibbs free energy is the energy available ("free") to do work. Any reaction that decreases the overall Gibbs free energy of a system is thermodynamically spontaneous.

tag: p

text: The function of the electron transport chain is to produce a transmembrane proton electrochemical gradient as a result of the redox reactions.[1] If protons flow back through the membrane, they enable mechanical work, such as rotating bacterial flagella. ATP synthase, an enzyme highly conserved among all domains of life, converts this mechanical work into chemical energy by producing ATP,[2] which powers most cellular reactions. A small amount of ATP is available from substrate-level phosphorylation, for example, in glycolysis. In most organisms the majority of ATP is generated in electron transport chains, while only some obtain ATP by fermentation.[citation needed]

text: In mitochondria[edit]

text: Most eukaryotic cells have mitochondria, which produce ATP from products of the citric acid cycle, fatty acid oxidation, and amino acid oxidation. At the mitochondrial inner membrane, electrons from NADH and FADH2 pass through the electron transport chain to oxygen, which is reduced to water. The electron transport chain comprises an enzymatic series of electron donors and acceptors. Each electron donor will pass electrons to a more electronegative acceptor, which in turn donates these electrons to another acceptor, a process that continues down the series until electrons are passed to oxygen, the most electronegative and terminal electron acceptor in the chain. Passage of electrons between donor and acceptor releases energy, which is used to generate a proton gradient across the mitochondrial membrane by actively "pumping" protons into the intermembrane space, producing a thermodynamic state that has the potential to do work. The entire process is called oxidative phosphorylation, since ADP is phosphorylated to ATP using the energy of hydrogen oxidation in many steps.

text: A small percentage of electrons do not complete the whole series and instead directly leak to oxygen, resulting in the formation of the free-radical superoxide, a highly reactive molecule that contributes to oxidative stress and has been implicated in a number of diseases and aging.

text: Mitochondrial redox carriers[edit]

text: Energy obtained through the transfer of electrons down the ETC is used to pump protons from the mitochondrial matrix into the intermembrane space, creating an electrochemical proton gradient (ΔpH) across the inner mitochondrial membrane (IMM). This proton gradient is largely but not exclusively responsible for the mitochondrial membrane potential (ΔΨM). It allows ATP synthase to use the flow of H+ through the enzyme back into the matrix to generate ATP from adenosine diphosphate (ADP) and inorganic phosphate. Complex I (NADH coenzyme Q reductase; labeled I) accepts electrons from the Krebs cycle electron carrier nicotinamide adenine dinucleotide (NADH), and passes them to coenzyme Q (ubiquinone; labeled Q), which also receives electrons from complex II (succinate dehydrogenase; labeled II). Q passes electrons to complex III (cytochrome bc1 complex; labeled III), which passes them to cytochrome c (cyt c). Cyt c passes electrons to Complex IV (cytochrome c oxidase; labeled IV), which uses the electrons and hydrogen ions to reduce molecular oxygen to water.

text: Four membrane-bound complexes have been identified in mitochondria. Each is an extremely complex transmembrane structure that is embedded in the inner membrane. Three of them are proton pumps. The structures are electrically connected by lipid-soluble electron carriers and water-soluble electron carriers. The overall electron transport chain:

text: Complex I[edit]

text: In Complex I (NADH:ubiquinone oxidoreductase, NADH-CoQ reductase, or NADH dehydrogenase; EC 1.6.5.3), two electrons are removed from NADH and ultimately transferred to a lipid-soluble carrier, ubiquinone (UQ). The reduced product, ubiquinol (UQH2), freely diffuses within the membrane, and Complex I translocates four protons (H+) across the membrane, thus producing a proton gradient. Complex I is one of the main sites at which premature electron leakage to oxygen occurs, thus being one of the main sites of production of superoxide.[3]

text: The pathway of electrons is as follows:

text: NADH is oxidized to NAD+, by reducing Flavin mononucleotide to FMNH2 in one two-electron step. FMNH2 is then oxidized in two one-electron steps, through a semiquinone intermediate. Each electron thus transfers from the FMNH2 to an Fe-S cluster, from the Fe-S cluster to ubiquinone (Q). Transfer of the first electron results in the free-radical (semiquinone) form of Q, and transfer of the second electron reduces the semiquinone form to the ubiquinol form, QH2. During this process, four protons are translocated from the mitochondrial matrix to the intermembrane space. [4] As the electrons become continuously oxidized and reduced throughout the complex an electron current is produced along the 180 Angstrom width of the complex within the membrane. This current powers the active transport of four protons to the intermembrane space per two electrons from NADH.[5]

text: Complex II[edit]

text: In Complex II (succinate dehydrogenase or succinate-CoQ reductase; EC 1.3.5.1) additional electrons are delivered into the quinone pool (Q) originating from succinate and transferred (via flavin adenine dinucleotide (FAD)) to Q. Complex II consists of four protein subunits: succinate dehydrogenase, (SDHA); succinate dehydrogenase [ubiquinone] iron-sulfur subunit, mitochondrial, (SDHB); succinate dehydrogenase complex subunit C, (SDHC) and succinate dehydrogenase complex, subunit D, (SDHD). Other electron donors (e.g., fatty acids and glycerol 3-phosphate) also direct electrons into Q (via FAD). Complex 2 is a parallel electron transport pathway to complex 1, but unlike complex 1, no protons are transported to the intermembrane space in this pathway. Therefore, the pathway through complex 2 contributes less energy to the overall electron transport chain process.

text: Complex III[edit]

text: In Complex III (cytochrome bc1 complex or CoQH2-cytochrome c reductase; EC 1.10.2.2), the Q-cycle contributes to the proton gradient by an asymmetric absorption/release of protons. Two electrons are removed from QH2 at the QO site and sequentially transferred to two molecules of cytochrome c, a water-soluble electron carrier located within the intermembrane space. The two other electrons sequentially pass across the protein to the Qi site where the quinone part of ubiquinone is reduced to quinol. A proton gradient is formed by one quinol (2H+2e-) oxidations at the Qo site to form one quinone (2H+2e-) at the Qi site. (in total four protons are translocated: two protons reduce quinone to quinol and two protons are released from two ubiquinol molecules).

text: When electron transfer is reduced (by a high membrane potential or respiratory inhibitors such as antimycin A), Complex III may leak electrons to molecular oxygen, resulting in superoxide formation.

text: Complex IV[edit]

text: In Complex IV (cytochrome c oxidase; EC 1.9.3.1), sometimes called cytochrome AA3, four electrons are removed from four molecules of cytochrome c and transferred to molecular oxygen (O2), producing two molecules of water. At the same time, eight protons are removed from the mitochondrial matrix (although only four are translocated across the membrane), contributing to the proton gradient. The activity of cytochrome c oxidase is inhibited by cyanide.

text: Coupling with oxidative phosphorylation[edit]

text:
According to the chemiosmotic coupling hypothesis, proposed by Nobel Prize in Chemistry winner Peter D. Mitchell, the electron transport chain and oxidative phosphorylation are coupled by a proton gradient across the inner mitochondrial membrane. The efflux of protons from the mitochondrial matrix creates an electrochemical gradient (proton gradient). This gradient is used by the FOF1 ATP synthase complex to make ATP via oxidative phosphorylation. ATP synthase is sometimes described as Complex V of the electron transport chain.[6] The FO component of ATP synthase acts as an ion channel that provides for a proton flux back into the mitochondrial matrix. It is composed of a, b and c subunits. Protons in the inter-membranous space of mitochondria first enters the ATP synthase complex through a subunit channel. Then protons move to the c subunits.[7] The number of c subunits it has determines how many protons it will require to make the FO turn one full revolution. For example, in humans, there are 8 c subunits, thus 8 protons are required.[8] After c subunits, protons finally enters matrix using a subunit channel that opens into the mitochondrial matrix.[7] This reflux releases free energy produced during the generation of the oxidized forms of the electron carriers (NAD+ and Q). The free energy is used to drive ATP synthesis, catalyzed by the F1 component of the complex.[9]
Coupling with oxidative phosphorylation is a key step for ATP production. However, in specific cases, uncoupling the two processes may be biologically useful. The uncoupling protein, thermogenin—present in the inner mitochondrial membrane of brown adipose tissue—provides for an alternative flow of protons back to the inner mitochondrial matrix. This alternative flow results in thermogenesis rather than ATP production.[10] Synthetic uncouplers (e.g., 2,4-dinitrophenol) also exist, and, at high doses, are lethal.[citation needed]

text: Summary[edit]

text: In the mitochondrial electron transport chain electrons move from an electron donor (NADH or QH2) to a terminal electron acceptor (O2) via a series of redox reactions. These reactions are coupled to the creation of a proton gradient across the mitochondrial inner membrane. There are three proton pumps: I, III, and IV. The resulting transmembrane proton gradient is used to make ATP via ATP synthase.

text: The reactions catalyzed by Complex I and Complex III work roughly at equilibrium. This means that these reactions are readily reversible, by increasing the concentration of the products relative to the concentration of the reactants (for example, by increasing the proton gradient). ATP synthase is also readily reversible. Thus ATP can be used to build a proton gradient, which in turn can be used to make NADH. This process of reverse electron transport is important in many prokaryotic electron transport chains.[11]

text: In bacteria[edit]

text: In eukaryotes, NADH is the most important electron donor. The associated electron transport chain is

text: NADH → Complex I → Q → Complex III → cytochrome c → Complex IV → O2 where Complexes I, III and IV are proton pumps, while Q and cytochrome c are mobile electron carriers. The electron acceptor is molecular oxygen.

text: In prokaryotes (bacteria and archaea) the situation is more complicated, because there are several different electron donors and several different electron acceptors. The generalized electron transport chain in bacteria is:

text: Note that electrons can enter the chain at three levels: at the level of a dehydrogenase, at the level of the quinone pool, or at the level of a mobile cytochrome electron carrier. These levels correspond to successively more positive redox potentials, or to successively decreased potential differences relative to the terminal electron acceptor. In other words, they correspond to successively smaller Gibbs free energy changes for the overall redox reaction Donor → Acceptor.

text: Individual bacteria use multiple electron transport chains, often simultaneously. Bacteria can use a number of different electron donors, a number of different dehydrogenases, a number of different oxidases and reductases, and a number of different electron acceptors. For example, E. coli (when growing aerobically using glucose as an energy source) uses two different NADH dehydrogenases and two different quinol oxidases, for a total of four different electron transport chains operating simultaneously.

text: A common feature of all electron transport chains is the presence of a proton pump to create a transmembrane proton gradient. Bacterial electron transport chains may contain as many as three proton pumps, like mitochondria, or they may contain only one or two. They always contain at least one proton pump.

text: Electron donors[edit]

text: In the present day biosphere, the most common electron donors are organic molecules. Organisms that use organic molecules as an energy source are called organotrophs. Organotrophs (animals, fungi, protists) and phototrophs (plants and algae) constitute the vast majority of all familiar life forms.

text: Some prokaryotes can use inorganic matter as an energy source. Such an organism is called a lithotroph ("rock-eater"). Inorganic electron donors include hydrogen, carbon monoxide, ammonia, nitrite, sulfur, sulfide, manganese oxide, and ferrous iron. Lithotrophs have been found growing in rock formations thousands of meters below the surface of Earth. Because of their volume of distribution, lithotrophs may actually outnumber organotrophs and phototrophs in our biosphere.

text: The use of inorganic electron donors as an energy source is of particular interest in the study of evolution. This type of metabolism must logically have preceded the use of organic molecules as an energy source.

text: Dehydrogenases[edit]

text: Bacteria can use a number of different electron donors. When organic matter is the energy source, the donor may be NADH or succinate, in which case electrons enter the electron transport chain via NADH dehydrogenase (similar to Complex I in mitochondria) or succinate dehydrogenase (similar to Complex II). Other dehydrogenases may be used to process different energy sources: formate dehydrogenase, lactate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, H2 dehydrogenase (hydrogenase), etc. Some dehydrogenases are also proton pumps; others funnel electrons into the quinone pool. Most dehydrogenases show induced expression in the bacterial cell in response to metabolic needs triggered by the environment in which the cells grow.[citation needed]

text: Quinone carriers[edit]

text: Quinones are mobile, lipid-soluble carriers that shuttle electrons (and protons) between large, relatively immobile macromolecular complexes embedded in the membrane. Bacteria use ubiquinone (the same quinone that mitochondria use) and related quinones such as menaquinone. Another name for ubiquinone is Coenzyme Q10.

text: Proton pumps[edit]

text: A proton pump is any process that creates a proton gradient across a membrane. Protons can be physically moved across a membrane; this is seen in mitochondrial Complexes I and IV. The same effect can be produced by moving electrons in the opposite direction. The result is the disappearance of a proton from the cytoplasm and the appearance of a proton in the periplasm. Mitochondrial Complex III uses this second type of proton pump, which is mediated by a quinone (the Q cycle).

text: Some dehydrogenases are proton pumps; others are not. Most oxidases and reductases are proton pumps, but some are not. Cytochrome bc1 is a proton pump found in many, but not all, bacteria (it is not found in E. coli). As the name implies, bacterial bc1 is similar to mitochondrial bc1 (Complex III).

text: Proton pumps are the heart of the electron transport process. They produce the transmembrane electrochemical gradient that enables ATP Synthase to synthesize ATP.

text: Cytochrome electron carriers[edit]

text: Cytochromes are pigments that contain iron. They are found in two very different environments.

text: Some cytochromes are water-soluble carriers that shuttle electrons to and from large, immobile macromolecular structures imbedded in the membrane. The mobile cytochrome electron carrier in mitochondria is cytochrome c. Bacteria use a number of different mobile cytochrome electron carriers.

text: Other cytochromes are found within macromolecules such as Complex III and Complex IV. They also function as electron carriers, but in a very different, intramolecular, solid-state environment.

text: Electrons may enter an electron transport chain at the level of a mobile cytochrome or quinone carrier. For example, electrons from inorganic electron donors (nitrite, ferrous iron, etc.) enter the electron transport chain at the cytochrome level. When electrons enter at a redox level greater than NADH, the electron transport chain must operate in reverse to produce this necessary, higher-energy molecule.

text: Terminal oxidases and reductases[edit]

text: When bacteria grow in aerobic environments, the terminal electron acceptor (O2) is reduced to water by an enzyme called an oxidase. When bacteria grow in anaerobic environments, the terminal electron acceptor is reduced by an enzyme called a reductase.

text: In mitochondria the terminal membrane complex (Complex IV) is cytochrome oxidase. Aerobic bacteria use a number of different terminal oxidases. For example, E. coli does not have a cytochrome oxidase or a bc1 complex. Under aerobic conditions, it uses two different terminal quinol oxidases (both proton pumps) to reduce oxygen to water.

text: Anaerobic bacteria, which do not use oxygen as a terminal electron acceptor, have terminal reductases individualized to their terminal acceptor. For example, E. coli can use fumarate reductase, nitrate reductase, nitrite reductase, DMSO reductase, or trimethylamine-N-oxide reductase, depending on the availability of these acceptors in the environment.

text: Most terminal oxidases and reductases are inducible. They are synthesized by the organism as needed, in response to specific environmental conditions.

text: Electron acceptors[edit]

text: Just as there are a number of different electron donors (organic matter in organotrophs, inorganic matter in lithotrophs), there are a number of different electron acceptors, both organic and inorganic. If oxygen is available, it is invariably used as the terminal electron acceptor, because it generates the greatest Gibbs free energy change and produces the most energy.[citation needed]

text: In anaerobic environments, different electron acceptors are used, including nitrate, nitrite, ferric iron, sulfate, carbon dioxide, and small organic molecules such as fumarate.

text: Since electron transport chains are redox processes, they can be described as the sum of two redox pairs. For example, the mitochondrial electron transport chain can be described as the sum of the NAD+/NADH redox pair and the O2/H2O redox pair. NADH is the electron donor and O2 is the electron acceptor.

text: Not every donor-acceptor combination is thermodynamically possible. The redox potential of the acceptor must be more positive than the redox potential of the donor. Furthermore, actual environmental conditions may be far different from standard conditions (1 molar concentrations, 1 atm partial pressures, pH = 7), which apply to standard redox potentials. For example, hydrogen-evolving bacteria grow at an ambient partial pressure of hydrogen gas of 10−4 atm. The associated redox reaction, which is thermodynamically favorable in nature, is thermodynamic impossible under "standard" conditions.[citation needed]

text: Summary[edit]

text: Bacterial electron transport pathways are, in general, inducible. Depending on their environment, bacteria can synthesize different transmembrane complexes and produce different electron transport chains in their cell membranes. Bacteria select their electron transport chains from a DNA library containing multiple possible dehydrogenases, terminal oxidases and terminal reductases. The situation is often summarized by saying that electron transport chains in bacteria are branched, modular, and inducible.

text: Photosynthetic[edit]

text: In oxidative phosphorylation, electrons are transferred from a low-energy electron donor (e.g., NADH) to an acceptor (e.g., O2) through an electron transport chain. In photophosphorylation, the energy of sunlight is used to create a high-energy electron donor and an electron acceptor. Electrons are then transferred from the donor to the acceptor through another electron transport chain.

text: Photosynthetic electron transport chains have many similarities to the oxidative chains discussed above. They use mobile, lipid-soluble carriers (quinones) and mobile, water-soluble carriers (cytochromes, etc.). They also contain a proton pump. It is remarkable that the proton pump in all photosynthetic chains resembles mitochondrial Complex III.

text: Photosynthetic electron transport chains are discussed in greater detail in the articles Photophosphorylation, Photosynthesis, Photosynthetic reaction center and Light-dependent reaction.

text: Summary[edit]

text: Electron transport chains are redox reactions that transfer electrons from an electron donor to an electron acceptor. The transfer of electrons is coupled to the translocation of protons across a membrane, producing a proton gradient. The proton gradient is used to produce useful work. About 30 work units are produced per electron transport.