Question

During the citric acid cycle, what happens to acetyl-CoA? It enters the citric acid cycle and gains carbon dioxide to form citric acid, and gains more carbon dioxide through redox reactions to form a 4-carbon molecule. It enters the citric acid cycle and associates with a 4-carbon molecule, forming citric acid, and then through redox reactions regenerates the 4-carbon molecule. It enters glycolysis and associates with a 5-carbon molecule through redox reactions, forming another acetyl-CoA molecule. It enters the citric acid cycle and associates with a 4-carbon molecule, forming a 5-carbon compound, and then through oxidation reactions regenerates the 4-carbon molecule.

Answer 1

The acetyl CoA produced from pyruvate moves into the citric acid cycle to combine with oxaloacetate containing four carbon molecules. This results in the formation of citric acid or citrate, which then undergoes a series of redox reactions to regenerate oxaloacetate.

Further explanation:

The citric acid cycle comprises a series of eight steps forming a closed loop. The four-carbon compound used in the initial step is regenerated in the final step of the cycle. During glycolysis, the pyruvate, which is produced, undergoes either fermentation or aerobic respiration. During aerobic respiration, the fate of pyruvate is to form either lactate or ethyl alcohol through fermentation. To enter the pathway of aerobic respiration, the pyruvate must be transformed into acetyl CoA. The acetyl CoA, thus formed, can enter to begin the cycle.

During the citric acid cycle:

1. Acetyl CoA (2C) reacts with oxaloacetate having four carbons to produce six carbon-containing compounds called citrate.
2. In the next step, citrate is changed into its isomer, which is isocitrate.
3. The isocitrate undergoes oxidation to form α-ketoglutarate (5C) while releasing carbon dioxide.
4. This is followed by a decarboxylation reaction and simultaneous addition of CoA to form succinyl CoA in the fourth step.
5. The succinate is formed from succinyl CoA when the later undergoes substrate-level phosphorylation.
6. In the sixth step, two hydrogen molecules are removed from succinate to form fumarate.
7. On the addition of a molecule of water, fumarate is transformed into malate.
8. The final step involves oxidation of malate to regenerate oxaloacetate, which was initially used in the reaction.
9. The cycle results in the overall production of one GTP or ATP, FADH2 and NADH in the reduced forms and two carbon dioxide molecules.

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Answer details:

Grade: High School

Chapter: The Citric Acid Cycle

Subject: Biology

Keywords:

Citric acid cycle, acetyl CoA, citrate, carbon dioxide, pyruvate, fermentation, aerobic respiration, substrate-level phosphorylation, NADH, FADH2, GTP, ATP.

Answer 2

The correct answer is: It enters the citric acid cycle and associates with a 4-carbon molecule (OXALOACETATE), forming citric acid, and then through redox reactions regenerates the 4-carbon molecule.

The citric acid cycle is a cyclic process (part of the cellular respiration) where acetyl CoA is modified in the mitochondria to produce high-energy intermediate molecules for the oxidative phosphorilation (production of ATP).