Question 1

Which of the following best describes the fate of the amino group during the catabolism of most amino acids in the human body?

Accepted Answer

It is transferred to $$\alpha-$$ketoglutarate to form glutamate via transamination.

Question 2

Which vitamin-derived coenzyme is essential for most transamination reactions?

Accepted Answer

Pyridoxal phosphate (PLP)

Question 3

In the urea cycle, which compound reacts with ammonia and carbon dioxide to form carbamoyl phosphate?

Accepted Answer

ATP

Question 4

Which of the following statements about ketogenic and glucogenic amino acids is correct?

Accepted Answer

Glucogenic amino acids yield intermediates that can enter the citric acid cycle and be used for gluconeogenesis.

Question 5

Which of the following is a direct product of oxidative deamination of glutamate?

Accepted Answer

Ammonia ($$\mathrm{NH}_3)$$

Question 6

A patient with a genetic defect in the enzyme ornithine transcarbamylase would most likely accumulate which compound?

Accepted Answer

Carbamoyl phosphate

Question 7

Which of the following best explains why the urea cycle is essential for terrestrial animals?

Accepted Answer

It converts toxic ammonia into a less toxic, water-soluble compound for excretion.

Question 8

Which of the following is NOT a product of the degradation of the heme portion of hemoglobin?

Accepted Answer

Aspartate

Question 9

Which of the following statements about the fate of amino acid carbon skeletons is correct?

Accepted Answer

Some carbon skeletons are converted to citric acid cycle intermediates.

Question 10

Which of the following is a key regulatory step in the urea cycle?

Accepted Answer

The synthesis of carbamoyl phosphate from ammonia, CO$$_2$$, and ATP

Question 11

Which of the following best describes the role of glutamine in nitrogen metabolism?

Accepted Answer

It is a major carrier of ammonia in the bloodstream.

Question 12

Which of the following is a correct statement about the conversion of amino acids to urea?

Accepted Answer

The amino group is first transferred to $$\alpha-$$ketoglutarate to form glutamate.

Question 13

Which of the following is a possible fate of the carbon skeleton of an amino acid after deamination?

Accepted Answer

Entry into the citric acid cycle as an intermediate

Question 14

Which of the following statements about the biosynthesis of nonessential amino acids is INCORRECT?

Accepted Answer

All but six of the standard amino acids can be biosynthesized from the essential amino acids only.

Question 15

Which of the following is a direct reactant in the formation of carbamoyl phosphate in the urea cycle?

Accepted Answer

Carbon dioxide

Question 16

Which of the following conversions could occur as part of a transamination reaction?

Accepted Answer

Pyruvate to alanine

Question 17

Which of the following is a nitrogen-containing product of oxidative deamination?

Accepted Answer

Ammonia ($$\mathrm{NH}_3)$$

Question 18

Which of the following statements about the compound urea is correct?

Accepted Answer

It is a white solid in the pure state.

Question 19

Which of the following is a product of the degradation of the heme portion of hemoglobin that gives feces its brown color?

Accepted Answer

Stercobilin

Question 20

Which of the following statements about amino acid metabolism is correct?

Accepted Answer

Amino acids can be converted to glucose via gluconeogenesis.

Protein Metabolism: Organic Chemistry of Amino Acid Catabolism and Urea Cycle

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