During the catabolism of most amino acids, the initial step involves the removal of the amino group. This process is crucial for channeling nitrogen into the urea cycle and converting the carbon skeleton for energy production. Which of the following best describes this initial step in amino acid catabolism?
Show answer and explanation
The answer
Correct answer: C. The amino group is transferred from the amino acid to an α-keto acid, typically α-ketoglutarate, forming a new α-keto acid and glutamate.
Tested concept: Amino acid catabolism and transamination
Explanation
The initial step in the catabolism of most amino acids is transamination. In this process, an aminotransferase enzyme transfers the amino group from the amino acid to an α-keto acid, most commonly α-ketoglutarate. This reaction produces a new α-keto acid (from the original amino acid) and glutamate (from α-ketoglutarate). Glutamate then serves as a central molecule for nitrogen excretion via the urea cycle. Distractor 1 is incorrect because direct oxidative deamination to release free ammonia is primarily a subsequent step, often involving glutamate dehydrogenase acting on glutamate, not the initial removal of the amino group from most amino acids. Distractor 2 describes decarboxylation, which is a different metabolic pathway for amino acids, leading to biogenic amines, not the primary catabolic route for nitrogen removal. Distractor 3 describes protein hydrolysis, which is the breakdown of proteins into individual amino acids, not the catabolism of a free amino acid.
io-med tracks every answer and builds your next set around the topics you miss.
Card required, nothing charged today. Then from $33/mo, auto-renews unless you cancel. Cancel in one click from Settings.