This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Metabolism of proline takes place in: 
Select and explain. 
A. Mitochondria, B. Cell membrane, C. Ribosome, D. All of the above
A: Mitochondria
Answer: A: Mitochondria 
Explanation: The catabolism of proline takes place in mitochodria. Since proline does not paicipate in transamination, the nitrogen of this imino acid is retained throughout its oxidation to 1-pyrolline-5-carboxylate, ring opening to glutamate--semialdehyde, and oxidation to glutamate, and is only removed during transamination of glutamate to a-ketoglutarate Ref: Harper 28th edition, chapter 29.