Which two amino acids are exclusively ketogenic, yielding acetyl-CoA or acetoacetyl-CoA with no net contribution to gluconeogenesis?

• A Phenylalanine and tyrosine
• B Isoleucine and tryptophan
• C Threonine and methionine
• D Leucine and lysine ✓

Explanation

Leucine and lysine are the only purely ketogenic amino acids. Leucine breaks down to acetyl-CoA and acetoacetate, while lysine yields acetoacetyl-CoA, and neither can supply carbon for glucose. Phenylalanine, tyrosine, isoleucine, tryptophan, threonine, and methionine are all both glucogenic and ketogenic, which eliminates options A, B, and C. This classification is examined frequently alongside maple syrup urine disease, where leucine accumulation drives the neurotoxicity.

Reference: Lippincott Illustrated Reviews: Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.