Question 1

Which enzyme is responsible for activating glycogen phosphorylase in response to glucagon or epinephrine signaling in muscle cells?

Accepted Answer

Phosphorylase b kinase

Question 2

During the digestion of dietary proteins, which hormone stimulates the secretion of HCl by parietal cells in the stomach?

Accepted Answer

Gastrin

Question 3

What is the role of pyridoxal phosphate (PLP) in aminotransferase-catalyzed reactions?

Accepted Answer

It alternates between an aldehyde and aminated form to accept and donate amino groups.

Question 4

Which of the following statements about amino acid storage in animals is correct?

Accepted Answer

Amino acids are not stored in the body and excess is degraded.

Question 5

In the urea cycle, which enzyme catalyzes the formation of carbamoyl phosphate from ammonium ions?

Accepted Answer

Carbamoyl phosphate synthetase I

Question 6

Which molecule typically accepts the amino group during transamination reactions in the liver?

Accepted Answer

α-Ketoglutarate ($$\alpha-$$ketoglutarate)

Question 7

What is the fate of the α-keto acids produced from amino acid oxidation?

Accepted Answer

They undergo oxidation to $$CO_2$$ and $$H_2O$$ for energy or provide carbon units for gluconeogenesis.

Question 8

Which of the following best describes the glucose-alanine cycle during vigorous muscle activity?

Accepted Answer

Alanine carries ammonia and pyruvate from muscle to liver, where ammonia is excreted and pyruvate is used for gluconeogenesis.

Question 9

Which of the following enzymes is inactivated by phosphorylation?

Accepted Answer

Glycogen synthase

Question 10

What is the primary function of glutamine in the bloodstream?

Accepted Answer

To transport excess ammonia safely to the liver, kidneys, and intestine.

Question 11

Which step in the urea cycle directly produces urea?

Accepted Answer

Arginase

Question 12

A patient with a deficiency in ornithine transcarbamoylase would most likely accumulate which metabolite?

Accepted Answer

Carbamoyl phosphate

Question 13

Which of the following statements about the regulation of glycogen synthesis is correct?

Accepted Answer

Glycogen synthase is active in its dephosphorylated form.

Question 14

Which metabolic circumstance leads to intentional breakdown of body proteins for amino acid catabolism?

Accepted Answer

Starvation or diabetes mellitus when carbohydrates are in short supply

Question 15

What is the main fate of ammonium ions released by glutamate dehydrogenase in the liver mitochondria?

Accepted Answer

They are excreted as urea via the urea cycle.

Question 16

Which of the following amino acids is exclusively ketogenic and not glucogenic?

Accepted Answer

Leucine

Question 17

Which process links the urea cycle to the citric acid cycle?

Accepted Answer

Aspartate-argininosuccinate shunt

Question 18

Which hormone stimulates the pancreas to secrete bicarbonate into the small intestine?

Accepted Answer

Secretin

Question 19

In muscle, which molecule allosterically activates glycogen phosphorylase to promote glucose release?

Accepted Answer

AMP

Question 20

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

Accepted Answer

It transfers the amino group from glutamate to pyruvate, forming alanine.

Amino Acid Oxidation and the Production of Urea: Digestion, Catabolism, and Nitrogen Disposal

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