Q: Which of the following is a correct equation for the transamination of glutamate with an a-keto acid?

$$\mathrm{Glutamate} + \mathrm{a\text{-}ketoacid} \rightarrow \mathrm{a\text{-}ketoglutarate} + \mathrm{a\text{-}aminoacid}$$

Question 1

Which process in the nitrogen cycle is responsible for converting atmospheric dinitrogen ($$N_2) $$into ammonia ($$NH_3) $$usable by living organisms?

Accepted Answer

Biological nitrogen fixation

Question 2

Why is nitrogen availability often a limiting factor for growth in most organisms?

Accepted Answer

Because dinitrogen ($$N_2) is $$abundant but few organisms can convert it to ammonia ($$NH_3)$$

Question 3

Which enzyme catalyzes the conversion of folate to tetrahydrofolate (THF), the active coenzyme in one-carbon metabolism?

Accepted Answer

Dihydrofolate reductase (DHFR)

Question 4

Tetrahydrofolate (THF) is essential in metabolism because it:

Accepted Answer

Carries activated one-carbon units for the formation of C-S, C-C, and C-N bonds

Question 5

A patient with a deficiency in the enzyme asparaginase is likely to have trouble with which metabolic process?

Accepted Answer

Degradation of asparagine to oxaloacetate

Question 6

Which of the following amino acids is considered essential in the human diet?

Accepted Answer

Leucine

Question 7

During protein turnover in mammals, what is the fate of most nitrogen from degraded proteins?

Accepted Answer

It is excreted in urine or incorporated into new proteins

Question 8

Which metabolic pathway is responsible for the conversion of excess ammonia to a less toxic compound for excretion in mammals?

Accepted Answer

Urea cycle (Krebs-Henseleit cycle)

Question 9

Transamination reactions in amino acid degradation typically result in the formation of which compound from the amino group?

Accepted Answer

a-Ketoglutarate

Question 10

Which of the following is a correct equation for the transamination of glutamate with an a-keto acid?

Accepted Answer

$$\mathrm{Glutamate} + \mathrm{a	ext{-}ketoacid} ightarrow \mathrm{a	ext{-}ketoglutarate} + \mathrm{a	ext{-}aminoacid}$$

Question 11

Which amino acids are degraded to pyruvate in mammals?

Accepted Answer

Alanine, cysteine, glycine, serine, threonine

Question 12

A child diagnosed with acute lymphoblastic leukemia is often treated with an enzyme that depletes asparagine. What is the rationale for this therapy?

Accepted Answer

Cancer cells cannot synthesize asparagine efficiently and rely on external sources

Question 13

Which coenzyme is derived from folic acid and is crucial for the transfer of one-carbon units in biosynthetic reactions?

Accepted Answer

Tetrahydrofolate (THF)

Question 14

Which amino acids are considered both glucogenic and ketogenic?

Accepted Answer

Isoleucine, phenylalanine, tryptophan, tyrosine

Question 15

What is the main function of the 20S proteasome in mammalian cells?

Accepted Answer

Degradation of intracellular proteins

Question 16

Which of the following statements about essential amino acids is correct?

Accepted Answer

They must be obtained from the diet because biosynthetic pathways are insufficient

Question 17

Which intermediate is a common precursor for the biosynthesis of several nonessential amino acids?

Accepted Answer

Intermediates of glycolysis and the citric acid cycle

Question 18

A mutation that impairs the urea cycle would most likely result in which clinical symptom?

Accepted Answer

Hyperammonemia

Question 19

Which of the following reactions is catalyzed by 5,10-methylenetetrahydrofolate?

Accepted Answer

Transfer of a methylene group to form new C-C bonds

Question 20

In the context of nitrogen metabolism, what is the significance of the experiment by Rudolf Schoenheimer using $$^{15}N-$$labeled tyrosine in rats?

Accepted Answer

It showed that nitrogen equilibrium is maintained through continuous protein turnover

Amino Acid and Nitrogen Metabolism: Biochemistry Study Notes

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