MCAT Biochemistry Question 141: Answer and Explanation

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Question: 141

6. Fatty acids enter the catabolic pathway in the form of:

  • A. glycerol.
  • B. adipose tissue.
  • C. acetyl-CoA.
  • D. ketone bodies.

Correct Answer: C

Explanation:

Fat molecules stored in adipose tissue can be hydrolyzed by lipases to fatty acids and glycerol. While glycerol can be converted into glyceraldehyde 3-phosphate, a glycolytic intermediate, a fatty acid must first be activated in the cytoplasm by coupling the fatty acid to CoA–SH, forming fatty acyl-CoA. The fatty acid is then transferred to a molecule of carnitine, which can carry it across the inner mitochondrial membrane. Once inside, the fatty acid is transferred to a mitochondrial CoA–SH, reforming fatty acyl-CoA. Through fatty acid oxidation, this fatty acyl-CoA can become acetyl-CoA, which enters the citric acid cycle.

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