Which of the following amino acids cannot be directly converted to pyruvate?

a. Glycine

b. Alanine

c. Tryptophan

d. Lysine

d. Lysine

Explanation:

Lysine,

Since it can not be synthesized by human body so it is essential in humans and must be obtained from diet. Catabolism of lysine takes place through one of several pathways, most common is saccharopine pathway which takes place in liver. The product formed is acetyl-CoA which is converted to pyruvate through ketogenic pathway.