Q: Which of the following reactions is catalyzed by glutamate dehydrogenase?

$$\text{Glutamate} + \text{NAD}^+ + \text{H}_2\text{O} \rightarrow \alpha\text{-ketoglutarate} + \text{NH}_4^+ + \text{NADH} + \text{H}^+$$

Question 1

Which of the following best describes the role of the E3 enzyme in the ubiquitin–proteasome pathway?

Accepted Answer

It transfers ubiquitin from E2 to the target protein, providing substrate specificity.

Question 2

A mutation in the gene encoding the E3 ubiquitin ligase results in the accumulation of a specific protein. Which disease is most likely associated with this defect?

Accepted Answer

Juvenile Parkinson disease

Question 3

Which of the following sequences is most likely to act as a degron, targeting a protein for rapid degradation?

Accepted Answer

A sequence rich in Pro, Glu, Ser, and Thr

Question 4

Which of the following best describes the fate of the α-amino group during amino acid degradation in terrestrial vertebrates?

Accepted Answer

It is converted into urea via the urea cycle.

Question 5

Which of the following statements about the 26S proteasome is correct?

Accepted Answer

The 19S regulatory subunit unfolds substrates and removes ubiquitin before degradation.

Question 6

A patient with a deficiency in carbamoyl phosphate synthetase I would most likely present with which of the following biochemical abnormalities?

Accepted Answer

Elevated blood ammonium (NH4+) levels

Question 7

Which of the following reactions is catalyzed by glutamate dehydrogenase?

Accepted Answer

$$	ext{Glutamate} + 	ext{NAD}^+ + 	ext{H}_2	ext{O} ightarrow \alpha	ext{-ketoglutarate} + 	ext{NH}_4^+ + 	ext{NADH} + 	ext{H}^+$$

Question 8

Which of the following amino acids is considered strictly ketogenic?

Accepted Answer

Leucine

Question 9

A defect in which enzyme would most likely result in the accumulation of phenylpyruvate in the urine?

Accepted Answer

Phenylalanine hydroxylase

Question 10

Which of the following best explains why protein catabolism is advantageous for migratory birds during long flights?

Accepted Answer

Protein catabolism provides more metabolic water than fat catabolism.

Question 11

Which of the following is a direct product of the action of serine dehydratase on serine?

Accepted Answer

Pyruvate

Question 12

Which of the following best describes the function of monooxygenases in amino acid degradation?

Accepted Answer

They incorporate one atom of O$$_2$$ into the substrate and one into water.

Question 13

Which of the following is a key regulatory molecule required for carbamoyl phosphate synthetase I activity in the urea cycle?

Accepted Answer

N-acetylglutamate

Question 14

A patient with maple syrup urine disease is unable to metabolize which of the following types of amino acids?

Accepted Answer

Branched-chain amino acids

Question 15

Which of the following best explains the neurological symptoms observed in untreated phenylketonuria (PKU)?

Accepted Answer

High phenylalanine inhibits transport of tyrosine and tryptophan into the brain.

Question 16

Which of the following best describes the linkage formed between ubiquitin and a target protein?

Accepted Answer

An isopeptide bond between the C-terminal glycine of ubiquitin and the ε-amino group of a lysine residue on the substrate

Question 17

Which of the following best describes the metabolic fate of fumarate produced in the urea cycle?

Accepted Answer

It enters the citric acid cycle and can be converted to oxaloacetate.

Question 18

Which of the following is a treatment for argininosuccinase deficiency?

Accepted Answer

Supplementing the diet with arginine

Question 19

Which of the following best explains why the urea cycle is considered evolutionarily related to nucleotide biosynthesis?

Accepted Answer

Several urea cycle enzymes are homologous to enzymes in pyrimidine and purine synthesis.

Protein Degradation and Amino Acid Catabolism: The Ubiquitin–Proteasome Pathway and Nitrogen Metabolism

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