Amino acids contain a special atom not found in the other major building blocks (glucose and fatty acids), and when oxidized this atom cannot be exhaled. Most of this special atom is excreted into the urine as part of the molecule called:单项选择题
A
protein
B
urea
C
nitric oxide gas
D
amino acids
E
it cannot be excreted

Question

Amino acids contain a special atom not found in the other major building blocks (glucose and fatty acids), and when oxidized this atom cannot be exhaled. Most of this special atom is excreted into the urine as part of the molecule called:单项选择题

A

protein

B

urea

C

nitric oxide gas

D

amino acids

E

it cannot be excreted

BlackTom AI · Accepted Answer

In this question, we’re focusing on what happens to the nitrogen-containing portion of amino acids after they are degraded. The prompt notes that amino acids have a special atom not found in glucose or fatty acids, and that when oxidized this atom cannot be exhaled. This points toward the nitrogen atom of the amino group that is processed through nitrogen metabolism pathways.
Option 1: protein. While proteins are made of amino acids and contain nitrogen, the statement here would imply that the nitrogen from amino acids is excreted as intact protein, which is not how nitrogen disposal works. Proteins are not excreted as a waste product in urine; they are broken down and the nitrogen is recycled or converted to other waste forms.
Option 2: urea. This is the classic nitrogenous waste product formed predominantly in the liver via the urea cycle. The majority of amino nitrogen is converted to urea and then excreted in urine. Urea formation is a key adaptation for safely removing excess nitrogen when amino acids are catabolized, especially after protein-rich meals or during fasting.
Option 3: nitric oxide gas. Nitric oxide is a signaling molecule produced from certain amino acids (notably arginine) and can be exhaled in trace amounts, but it is not the primary route by which excess nitrogen is disposed of. Its production is regulated and purpose-driven, rather than serving as the main excretory form of nitrogen.
Option 4: amino acids. The idea that nitrogen is excreted as free amino acids isn’t correct for humans. Amino acids are primarily catabolized to remove nitrogen, and the remaining nitrogen is converted to urea (and some creatinine, ammonia in other contexts) rather than being excreted as intact amino acids in urine.
Option 5: it cannot be excreted. This is inaccurate because humans do excrete nitrogenous waste; the body has specific pathways to dispose of nitrogen, with urea being the main end product in most organisms capable of forming urea.
Overall, the options contrast the concept of nitrogen disposal versus direct excretion of larger molecules or signaling gases. The most consistent description with mammalian nitrogen excretion is that the nitrogen from amino acid catabolism is converted into a soluble waste product suitable for urine excretion, namely urea.

Amino acids contain a special atom not found in the other major building blocks (glucose and fatty acids), and when oxidized this atom cannot be exhaled. Most of this special atom is excreted into the urine as part of the molecule called:单项选择题

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