7.3 Oxidation of Pyruvate and the Citric Acid Cycle

7.3 Oxidation of Pyruvate and the Citric Acid Cycle

  • This step is catalyzed by an isomerase.
  • The ninth step is enolase's job.
    • The dehydration reaction caused by this enzyme leads to the formation of a double bond that increases the potential energy in the remaining phosphate bond and the production ofPEP.
  • The last step in glycolysis involves the reverse reaction of pyruvate's conversion into PEP and the production of a second ATP molecule by the compound pyruvic.
    • The reverse reactions are named for the enzymes that can do both forward and reverse reactions.
  • You can see the process in action to gain a better understanding of the breakdown of sugar.
  • Two pyruvate molecule, four new ATP molecule, and two molecule of NADH are produced by Glycolysis.
  • If the cell can't catabolize the pyruvate molecule further, it won't be able to harvest any more of the sugar.
    • The process in which organisms convert energy in the presence of oxygen is their sole source of energy.
    • These cells lose their ability to maintain their pumps if glycolysis is interrupted.
  • If pyruvate kinase is not available in sufficient quantities, the last step will not happen.
    • In this situation, the entire pathway will go on, but only two of them will be made in the second half.
    • pyruvate kinase is a rate-limiting enzyme.
  • Aerobic respiration will go forward if oxygen is available.
    • The pyruvate molecule produced at the end of glycolysis is transported into the mitochondria, which are the sites of cellular respiration.
    • There, pyruvate is transformed into an acetyl group that will be picked up and activated by a carrier compound called CoA.
    • CoA is derived from pantothenic acid.
    • The major function of Acetyl CoA is to deliver the acetyl group from pyruvate to the next stage of the pathway.
  • To enter the next pathway, pyruvate must undergo several changes.
    • The conversion is a three-step process.
  • A molecule of carbon dioxide is released when a carboxyl group is removed from pyruvate.
    • The two-carbon hydroxyethyl group is bound to the pyruvate dehydrogenase.
    • This is the first carbon from the original molecule to be removed.
  • The hydroxyethyl group is oxidation to an acetyl group, and the electrons are picked up by NAD+.
    • The high-energy electrons from NADH will be used later.
  • A molecule of acetyl CoA is produced when the acetyl group is transferred to CoA.
  • A multienzyme complex converts pyruvate into acetyl CoA when it enters the mitochondrial matrix.
    • One molecule of NADH is formed when carbon dioxide is released.
  • One of the major end products of cellular respiration is carbon dioxide, which is produced when a carbon atom is removed.
  • In the presence of oxygen, acetyl CoA delivers its acetyl (2C) group to a four-carbon molecule, oxaloacetate, to form citrate, a sixcarbon molecule with three carboxyl groups.
  • The citric acid cycle is similar to the conversion of pyruvate to acetyl CoA.
    • The only exception to the fact that almost all of the citric acid cycle's enzymes aresoluble is the one that is embedded in the innerchondrion.
    • The last part of the pathway regenerates the compound used in the first step of the citric acid cycle.
    • The eight steps of the cycle are a series of dehydration, hydration, and decarboxylation reactions that produce two carbon dioxide molecules, one GTP/ATP, and the reduced carriers.
    • The NADH and FADH2 produced must transfer their electrons to the next pathway in the system in order to be considered an aerobic pathway.
    • The oxidation steps of the citric acid cycle do not occur if this transfer does not occur.
    • The citric acid cycle does not directly consume oxygen.
  • The acetyl group from acetyl CoA is attached to a four-carbon oxacetatealo molecule to form a six-carbon citrate molecule.
    • The acetyl group is fed into the cycle through a series of steps.
    • One FAD molecule is reduced to FADH2, and one ATP or GTP is produced, depending on the cell type.
    • The citric acid cycle runs continuously because the first reactant is the final product.
    • A transitional phase occurs when pyruvic acid is converted to acetyl CoA.
    • The condensation step combines the two-carbon acetyl group with a four-carbon oxaloacetate molecule to form a six-carbon molecule of citrate.
    • CoA diffuses away to combine with another acetyl group.
    • This step is irreversible because it is exergonic.
    • The rate of the reaction is controlled by the amount of ATP available.
    • The rate of this reaction will decrease if the levels of ATP increase.
    • The rate increases if the supply is short.
  • In step two, citrate is converted into its isomer, isocitrate, as it loses one water molecule.
  • A five-carbon molecule, a-ketoglutarate, along with a molecule of CO2 and two electrons, is produced by isocitrate in step three.
    • This step is regulated by negative feedback and a positive effect ofADP.