Deck 18: Nitrogen Metabolism

Question 1

How many ATP and electrons are required for the reduction of one molecule of nitrogen to two molecules of ammonia in the reaction catalyzed by nitrogenase?

A) 8 ATP and 8 electrons
B) 16 ATP and 8 electrons
C) 16 ATP and 16 electrons
D) 8 ATP and 16 electrons
E) 16 ATP and 6 electrons

Answer 1

16 ATP and 8 electrons

Question 2

Which of the following are required by nitrogenase to carry out the reduction of nitrogen?

A) an iron-molybdenum cofactor
B) iron-sulfur centers
C) a strong reducing agent such as ferredoxin
D) the absence of oxygen
E) all of the above

Answer 2

all of the above

Question 3

In the process of nitrification, nitrate reductase converts _____ into _____.

A) nitrate; nitrogen
B) nitrate; ammonia
C) nitrate; nitrite
D) nitrate; nitric oxide
E) nitrogen; nitrate

Answer 3

nitrate; nitrite

Question 4

Given the following reaction, what is the missing product of the net reaction of glutamine synthetase and glutamate synthase?
$\alpha$ -ketoglutarate + NH₄⁺ + NADPH + ATP $\rarr$ NADP⁺ + ADP + P_i + _____

A) aspartate
B) asparagine
C) glutamate
D) glutamine
E) none of the above

Question 5

What are the products of the following transamination reaction?
$\alpha$ -ketoglutarate + alanine _____ + _____

A) aspartate; oxaloacetate
B) glutamate; oxaloacetate
C) aspartate; pyruvate
D) glutamate; pyruvate
E) none of the above

Question 6

What amino acid is attached to the pyridoxal-5'-phosphate in a typical transaminase?

A) Ser
B) His
C) Arg
D) Gln
E) Lys

Question 7

When the transaminase enzyme is in the _____ form, it will only react with _____.

A) pyridoxal; $\alpha$ -keto acid
B) pyridoxal; $\alpha$ -amino acid
C) pyridoxamine; $\alpha$ -amino acid
D) pyridoxal; $\beta$ -keto acid
E) pyridoxamine; $\beta$ -amino acid

Question 8

Which of the following nonessential amino acids is correctly paired with the essential amino acid that is required for its synthesis?

A) Phe: Trp
B) Cys: Met
C) Ser: Gly
D) Asp: Glu
E) His: Gln

Question 9

Which of the following amino acids is properly paired with the amino acid from which it is derived?

A) Gln: Asp
B) Pro: Ala
C) Arg: Lys
D) Tyr: Phe
E) Ser: Cys

Question 10

What coenzyme is required for the conversion of serine to glycine?

A) pyridoxal phosphate
B) lipoic acid
C) tetrahydrofolate
D) biotin
E) cobalamin

Question 11

What form of the folate coenzyme is required for the conversion of homocysteine to methionine?

A) methyl-tetrahydrofolate
B) methylene-tetrahydrofolate
C) methenyl-tetrahydrofolate
D) formyl-tetrahydrofolate
E) dihydrofolate

Question 12

Which of the following amino acids cannot be produced in a plant that has been treated with glyphosate?

A) Cys
B) Phe
C) Leu
D) Arg
E) Pro

Question 13

What amino acid is the precursor for the neurotransmitters epinephrine and norepinephrine?

A) tryptophan
B) serine
C) tyrosine
D) aspartate
E) glutamate

Question 14

Which of the following neurotransmitters is correctly paired with the amino acid from which it is synthesized?

A) dopamine: tyrosine
B) $\gamma$ -aminobutyric acid: glutamate
C) serotonin: tryptophan
D) epinephrine: tyrosine
E) all of the above

Question 15

The molecule _____ which is synthesized from _____, stimulate vasodilation.

A) nitric oxide; arginine
B) nitrous oxide; arginine
C) nitric oxide; citrulline
D) nitrous oxide; citrulline
E) none of the above

Question 16

Which of the following correctly describes the general synthesis of purine nucleotides?

A) The basic ring structure, orotate, is synthesized and then linked to PRPP
B) The basic ring structure, orotate, is synthesized stepwise on PRPP
C) The basic ring structure, inosine, is synthesized and then linked to PRPP
D) The basic ring structure, inosine, is synthesized stepwise on PRPP
E) none of the above

Question 17

What are the products of the glycine cleavage system?

A) formyl-tetrahydrofolate, ammonia and carbon dioxide
B) methylene-tetrahydrofolate, ammonia and carbon dioxide
C) methyl-tetrahydrofolate, ammonia and carbon dioxide
D) methylene-tetrahydrofolate and carbamoyl phosphate
E) methyl-tetrahydrofolate and carbamoyl phosphate

Question 18

Threonine is considered both ketogenic and glucogenic because it is converted to _____ and _____.

A) pyruvate; acetyl-CoA
B) ammonia; acetoacetate
C) carbamoyl phosphate; acetoacetate
D) glycine; acetyl-CoA
E) glycine; glutaryl-CoA

Question 19

The enzyme _____ is missing in phenylketonuria while _____ is missing in alkaptonuria.

A) tyrosine transaminase; phenylalanine hydroxylase
B) phenylalanine hydroxylase; p-hydroxy-phenylpyruvate dioxygenase
C) phenylalanine hydroxylase; homogentisate oxidase
D) p-hydroxy-phenylpyruvate dioxygenase; homogentisate oxidase
E) homogentisate oxidase; tyrosine transaminase

Question 20

The amino acids metabolized by the branched chain keto acid dehydrogenase complex are _____.

A) Val, Leu and Ile
B) Thr, Val and Pro
C) Pro, Leu and Met
D) Ile, Thr and Pro
E) none of the above

Question 21

Based upon the following, what is the net ATP production for the synthesis of one molecule of urea in the urea cycle? Consider that one nitrogen atom comes from glutamate dehydrogenase and the other comes from aspartate.
The conversion of fumarate to oxaloacetate gives 1 NADH (oxaloacetate is transaminated to aspartate)
Carbamoyl phosphate synthesis requires 2 ATP equivalents
Argininosuccinate synthesis requires 2 ATP equivalents
Glutamate dehydrogenase produces 1 NADH

A) -4 ATP
B) -1.5 ATP
C) -1 ATP
D) +1 ATP
E) +3 ATP