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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.
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