Amino Group Removal in Urea Synthesis

Steps:

• Amino acids undergo deamination, removing the amino group to release ammonia.
• Ammonia is toxic and converted to urea via the urea cycle in the liver.
• The amino group (NH2) from the alpha carbon is the source of nitrogen for urea.
• Other parts like the carboxyl group form keto acids for energy or glucose.

Why A is correct:

• The amino group provides the nitrogen atoms incorporated into urea, as per the urea cycle formula: 2NH3 + CO2 → H2N-CO-NH2 + H2O.

Why the others are wrong:

• B (carboxyl group): Forms alpha-keto acids, not used in urea production.
• C (R group): Retained in the carbon skeleton for metabolism, unrelated to urea.
• D (alpha carbon): Forms the backbone of metabolites, not removed for urea.

Final answer: A