If pyruvate oxidation is blocked, what will happen to the levels of oxaloacetate and citrate in the citric acid cycle? 1 point There will be no change in the levels of oxaloacetate and citric acid. Oxaloacetate will decrease and citric acid will accumulate. Oxaloacetate will accumulate and citric acid will decrease. Both oxaloacetate and citric acid will decrease. Both oxaloacetate and citric acid will accumulate
The Correct Answer and Explanation is:
Correct Answer: Oxaloacetate will accumulate and citric acid will decrease.
Explanation:
The citric acid cycle (also called the Krebs cycle or tricarboxylic acid cycle) is a central metabolic pathway that operates in the mitochondria and is crucial for cellular respiration. Before entering the citric acid cycle, glucose undergoes glycolysis in the cytoplasm, producing two molecules of pyruvate per glucose molecule. Pyruvate is then transported into the mitochondria, where it undergoes pyruvate oxidation to form acetyl-CoA, which is the key substrate for the citric acid cycle.
During pyruvate oxidation, each pyruvate molecule is converted into one molecule of acetyl-CoA by the pyruvate dehydrogenase complex. This reaction also produces NADH and releases CO₂. Acetyl-CoA then combines with oxaloacetate (a four-carbon molecule) to form citrate (a six-carbon molecule) in the first step of the citric acid cycle, catalyzed by the enzyme citrate synthase.
If pyruvate oxidation is blocked, acetyl-CoA is no longer produced from pyruvate. Without acetyl-CoA, the citric acid cycle cannot proceed because there is no substrate to combine with oxaloacetate to form citrate. As a result:
- Citrate levels decrease because the synthesis of citrate from oxaloacetate and acetyl-CoA is halted.
- Oxaloacetate accumulates because it is not being used to form citrate.
Therefore, blocking pyruvate oxidation disrupts the flow of the citric acid cycle at the very beginning. While other pathways can sometimes feed into the cycle, such as fatty acid oxidation producing acetyl-CoA, in a scenario where pyruvate oxidation is blocked and no alternative sources of acetyl-CoA are available or sufficient, the net effect is a buildup of oxaloacetate and a reduction in citrate levels.
This metabolic block also affects ATP production and the availability of intermediates for biosynthetic processes, highlighting the critical role of pyruvate oxidation in cellular metabolism.
