$$\text{Glutamate} + \text{NH}_4^+ + \text{ATP} \rightarrow \text{Glutamine} + \text{ADP} + \text{Pi}$$

$$\text{Amino acid}_1 + \text{\alpha-ketoglutarate} \rightarrow \text{\alpha-keto acid}_1 + \text{Glutamate}$$

$$\text{Glutamate} + \text{NAD}^+ + \text{H}_2O \rightarrow \text{\alpha-ketoglutarate} + \text{NH}_4^+ + \text{NADH} + \text{H}^+$$

Question 1

Which enzyme is responsible for converting glutamate to glutamine for transport to the liver?

Accepted Answer

Glutamine synthetase

Question 2

What is the overall reaction catalyzed by glutamine synthetase?

Accepted Answer

$$	ext{Glutamate} + 	ext{NH}_4^+ + 	ext{ATP} ightarrow 	ext{Glutamine} + 	ext{ADP} + 	ext{Pi}$$

Question 3

Which molecule is used to transport excess nitrogen from muscle to the liver?

Accepted Answer

Alanine

Question 4

In the glucose-alanine cycle, what is the fate of alanine in the liver?

Accepted Answer

It is converted to pyruvate and ammonia

Question 5

Which enzyme catalyzes the conversion of glutamine to glutamate in the liver, releasing ammonia?

Accepted Answer

Glutaminase

Question 6

What is the main purpose of the urea cycle in amino acid metabolism?

Accepted Answer

To convert toxic ammonia to urea for excretion

Question 7

Which of the following reactions is catalyzed by a transaminase enzyme?

Accepted Answer

$$	ext{Amino acid}_1 + 	ext{\alpha-ketoglutarate} ightarrow 	ext{\alpha-keto acid}_1 + 	ext{Glutamate}$$

Question 8

Which intermediate of the citric acid cycle can be converted to aspartate for entry into the urea cycle?

Accepted Answer

Oxaloacetate

Question 9

A patient with elevated blood ammonia levels may have a defect in which metabolic pathway?

Accepted Answer

Urea cycle

Question 10

Which of the following is a correct description of the glucose-alanine cycle?

Accepted Answer

Muscle exports alanine to the liver, where it is converted to pyruvate and ammonia; pyruvate is used for gluconeogenesis.

Question 11

Which of the following is a product of the reaction catalyzed by glutaminase?

Accepted Answer

Ammonia ($$	ext{NH}_4^+)$$

Question 12

Which of the following conditions can lead to increased blood levels of AST and ALT?

Accepted Answer

Liver damage due to heart attack or infection

Question 13

Which of the following reactions is an example of oxidative deamination?

Accepted Answer

$$	ext{Glutamate} + 	ext{NAD}^+ + 	ext{H}_2O ightarrow 	ext{\alpha-ketoglutarate} + 	ext{NH}_4^+ + 	ext{NADH} + 	ext{H}^+$$

Question 14

Which of the following is NOT a function of transaminase enzymes?

Accepted Answer

Directly producing ammonia from amino acids

Question 15

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

Accepted Answer

It acts as a carrier of ammonia from peripheral tissues to the liver.

Question 16

Which of the following is a consequence of a defect in the urea cycle?

Accepted Answer

Hyperammonemia

Question 17

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

Accepted Answer

Fumarate can enter the citric acid cycle and be converted to aspartate.

Question 18

Which of the following is a correct sequence of events in the transport of nitrogen from muscle to liver?

Accepted Answer

Amino acids are transaminated to form alanine, which is transported to the liver and converted to pyruvate and ammonia.

Question 19

Which of the following is a key diagnostic marker for liver damage?

Accepted Answer

Elevated levels of AST and ALT in the blood

Question 20

Which of the following best explains why ammonia must be converted to urea in the body?

Accepted Answer

Ammonia is highly toxic, especially to the brain, and urea is much less toxic and can be safely excreted.

Amino Acid Oxidation and Nitrogen Metabolism

Study Guide - Practice Questions