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Chapter 9 Cellular Respiration and Fermentation

The enzyme that converts acetyl coa to citrate is

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The enzyme that converts acetyl CoA to citrate is shut down when ATP binds to it. (Feedback Inhibition) Feedback inhibition also occurs at two points later in the cycle: 1. NADH binds to the enzyme's active site. (Competitive Inhibition) 2. ATP binds to an allosteric regulatory site. The citric acid cycle can be turned off at multiple points, via several different mechanisms of feedback inhibition. The TCA cycle starts with acetyl and ends with CO 2 . The reactions occur in the mitochodrial matrix, and the potential energy that is released is used to produce NADH, FADH 2 , and ATP or GTP. What Happens to the NADH and FADH 2 ? Glycolysis, pyruvate processing, and the citric acid cycle transfer electrons from glucose to NAD + and FAD, creating NADH and FADH 2 . These molecules then carry the electrons to oxygen, which serves as the final electron acceptor in eukaryotic cells. NADH is oxidized in the inner membrane of the mitochondria and the membranes of cristae. In prokaryotes, the oxidation of NADH occurs in the plasma membrane.
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Components of the Elctron Transport Chain Collectively, the molecules responsible for the oxidation of NADH and FADH 2 are designated the electron transport chain (ETC). As electrons are passed from one protein to another in the chain, the energy released by the redox reactions is used to pump protons across the inner membrane of mitochondria. After the proton gradient is established, a stream of protons through the enzyme ATP synthase makes part of the protein spin, driving the production of ATP from ADP and P i . Because this mode of ATP production links the phosphoylation of ADP with the oxidation of NADH and FADH 2 , it is called oxidative phosphorylation. The inner membrane of the mitochondrion also contains a molecule called ubiquinone, which is not a protein. Also called coenzyme Q or simply Q, ubiquinone consists of a carbon-containing ring attached to a long tail made up of isoprene subunits. The long, isoprene-rich tail is hydrophobic, therefore, Q is lipid soluble and can move throughout the mitochondrial membrane efficiently. In contrast, all but one of the proteins in the ETC are embedded in the membrane. Electrons step down in potential energy from the elctron carriers NADH and FADH 2 through an electron transport chain to a final electron acceptor. When oxygen is the final electron acceptor, water is formed. The Chemiosmosis Hypothesis Mitchell's hypothesis was that the real job of the electron transport chain is to pump protons from the matrix of the mitochondrion through the inner membrane and out to the intermembrance space or the interior of cristae. The intermembrane space and the inside of the cristae would become positively charged relative to the matrix and would have a much higher concentration of protons. Te result would be a strong electrochemical gradient favoring the movement of protons back into the matrix. Mitchell hypothesized that an enzyme in the inner membrane uses this proton-motive force to synthesize
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The enzyme that converts acetyl CoA to citrate is shut down...

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