This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
Amino acid which is both glucogenic and ketogenic 
Select and explain. 
A. Leucine, B. Alanine, C. Serine, D. Tryptophan
D: Tryptophan
Answer: D: Tryptophan 
Explanation: During metabolism pa of the carbon skeleton of tryptophan enter the ketogenic pathway and other pas to glucogenic pathway. Leucine is purely ketogenic. It is conveed to ketone bodies. remaining amino acid enter only into glucogenic pathwayRef: DM Vasudevan - Textbook of Biochemistry for Medical Students, 7th edition, page no: 27