Q: Which of the following reactions is catalyzed by alanine aminotransferase?

$$\mathrm{Alanine + \alpha\text{-}ketoglutarate \rightarrow pyruvate + glutamate}$$

Question 1

Which α-keto acid is produced when alanine undergoes transamination with α-ketoglutarate?

Accepted Answer

Pyruvate

Question 2

In the alanine aminotransferase assay, why is an excess of lactate dehydrogenase and NADH included in the reaction mixture?

Accepted Answer

To ensure that the disappearance of NADH directly reflects the disappearance of alanine

Question 3

Why are alanine and glutamine present in higher concentrations in human blood plasma compared to other amino acids?

Accepted Answer

They serve as major carriers of nitrogen from peripheral tissues to the liver

Question 4

Which of the following best explains the rise in blood ammonia levels in cats fed a diet lacking arginine?

Accepted Answer

Arginine is required for the urea cycle, and its absence prevents ammonia detoxification

Question 5

Which organ transplant would most effectively alleviate the symptoms of maple syrup urine disease, and why?

Accepted Answer

Liver, because it contains the enzymes needed to metabolize branched-chain amino acids

Question 6

During the complete oxidation of alanine to CO$$_2$$ and H$$_2O$$, including the cost of nitrogen excretion as urea, which substrate yields more net ATP: lactate or alanine?

Accepted Answer

Lactate yields more net ATP because alanine oxidation requires ATP for urea synthesis

Question 7

Which of the following best describes the role of pyridoxal phosphate in the reaction catalyzed by serine hydroxymethyltransferase?

Accepted Answer

It acts as a coenzyme, forming a Schiff base with the amino acid substrate

Question 8

Aspartate aminotransferase has the highest activity among liver aminotransferases because:

Accepted Answer

It is essential for both amino acid metabolism and the malate-aspartate shuttle

Question 9

Which of the following is the correct sequence of intermediates in the degradation of isoleucine to propionyl-CoA and acetyl-CoA, analogous to β-oxidation and the citric acid cycle?

Accepted Answer

Transamination, oxidative decarboxylation, dehydrogenation, hydration, cleavage

Question 10

Ornithine can substitute for arginine in the diet of cats because:

Accepted Answer

Ornithine is an intermediate in the urea cycle and can regenerate arginine

Question 11

Which of the following reactions is catalyzed by alanine aminotransferase?

Accepted Answer

$$\mathrm{Alanine + \alpha	ext{-}ketoglutarate ightarrow pyruvate + glutamate}$$

Question 12

Which of the following best describes why arginine is considered an essential amino acid in cats?

Accepted Answer

Cats cannot synthesize sufficient arginine to meet their metabolic needs

Question 13

Which of the following best explains why the absence of arginine in the diet leads to ammonia toxicity in cats?

Accepted Answer

The urea cycle is blocked, preventing ammonia detoxification

Question 14

Which of the following is a correct analogy between isoleucine degradation and the citric acid cycle or β-oxidation?

Accepted Answer

The oxidative decarboxylation of α-keto-β-methylvalerate is analogous to the conversion of α-ketoglutarate to succinyl-CoA

Question 15

Which of the following best describes the mechanism of serine hydroxymethyltransferase in the conversion of serine to glycine?

Accepted Answer

Serine transfers a one-carbon unit to tetrahydrofolate, forming glycine and N$$^5$$,N$$^{10}-$$methylene-THF

Question 16

Which of the following is the correct net reaction for the transamination of aspartate with α-ketoglutarate?

Accepted Answer

$$\mathrm{Aspartate + \alpha	ext{-}ketoglutarate ightarrow oxaloacetate + glutamate}$$

Biochemistry Study Guidance for Amino Acid Metabolism and Enzyme Mechanisms

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