Question

A young dog has never had much energy. He is brought to a veterinarian for help and she decides to conduct several diagnostic tests. She discovers that the dog's mitochondria can use only fatty acids and amino acids for respiration, and his cells produce more lactate than normal. Of the following, which is the best explanation of the dog's condition? A) His cells cannot move NADH from glycolysis into the mitochondria. B) His mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane. C) His cells have a defective electron transport chain, so glucose goes to lactate instead of to acetyl CoA. D) His cells lack the enzyme in glycolysis that forms pyruvate.

Answer 1

Answer: B

Explanation:

Under aerobic conditions, pyruvate is converted to acetyl CoA which enters the TCA cycle to be oxidized to carbon IV oxide.

Glycolysis takes place in the cytoplasm. So pyruvate is generated in the cytoplasm. This is transported into the mitochondria by pyruvate transporter.

For pyruvate to be decarboxylated to acetyl CoA in the mitochondria, a transport protein found on the cell membrane of mitochondria is needed to transport pyruvate across the inner membrane of mitochondria for pyruvate dehydrogenase reaction.

Answers is that the dog’s mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane.

When pyruvate is not converted to acetyl CoA, it will increase the level of lactate and/or alanine in anaerobic conditions.