Chapter 18 Amino Acid and Nitrogen Metabolism

N2 gas can be converted to NH3 by:

A) most organisms.

B) mammals.

C) all plants.

D) all bacteria.

E) legumes.

E

Nitrate can be reduced to ammonia by virtually all organisms.

FALSE

Which of the following enzymes is NOT involved in the conversion of NH3 to an organic

nitrogen-containing compound?

A) Glutamate dehydrogenase

B) Carbamoyl phosphate dehydrogenase

C) Glutamate-oxaloacetate transaminase

D) Glutamine synthetase

E) Asparagine synthetase

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C

Nitrogen fixation requires the hydrolysis of 8 ATPs to produce 2 NH3 molecules from 1 N2.

TRUE

The proteasome is a large multisubunit ATP-dependent protease that degrades proteins that

have been modified by the attachment of ________.

ubiquitin

Pyridoxal phosphate is a versatile coenzyme as it is capable of forming a stable ________

base between an amino acid substrate and the coenzyme.

Schiff

Tetrahydrofolate is a coenzyme involved in the mobilization and utilization of single carbon

functional units in the:

A) metabolism of serine, glycine, methionine, and histidine.

B) biosynthesis of purine nucleotides.

C) biosynthesis of thymine.

D) biosynthesis of formylmethionyl-tRNA.

E) all of the above.

E

In the degradation of amino acids in muscle NH4

+ is carried to the liver for conversion into

urea by:

A) glutamine.

B) asparagine.

C) alanine.

D) either alanine or glutamine.

E) any amino acid

C

Transamination reactions can be used to degrade or synthesize amino acids because they have

an ________ that has a value close to one.

equilibrium constant

With appropriate nutrition, animals maintain nitrogen intake and excretion at equivalent

rates.

TRUE

The Krebs-Henseleit urea cycle takes place in liver cells entirely within the mitochondrion.

FALSE

In mammals excess dietary protein is degraded with amino acid nitrogen being excreted as

________.

UREA

________ high energy phosphates from ATP are consumed in each turn of the urea cycle.

FOUR

Which of the following amino acids is both glucogenic and ketogenic?

A) Lysine

B) Leucine

C) Tryptophan

D) Cysteine

E) Arginine

C

Which of the following amino acids cannot be used to provide an intermediate of the citric

acid cycle?

A) Histidine

B) Proline

C) Phenylalanine

D) Lysine

E) Tyrosine

D

The H2S produced by metabolism of cysteine is a waste product with no physiological or

biochemical function.

FALSE

The oxidation of branched chain amino acids shares a similar chemical strategy with β-

oxidation of fatty acids.

TRUE

The common degradation product of lysine, tryptophan, phenylalanine and tyrosine is

________.

acetoacetate

Arginine and methionine can be synthesized by mammals but are generally classed as

essential amino acids.

TRUE

All amino acids can be synthesized from intermediates of the:

A) glycolytic pathway alone.

B) glycolytic pathway and the pentose phosphate pathway.

C) citric acid cycle alone.

D) the glycolytic pathway and citric acid cycle.

E) the glycolytic pathway, the pentose phosphate pathway and citric acid cycle.

E

Folate deficiency results in increased risk of cardiovascular disease associated with

abnormally high levels of serum ________ due to decreased levels of tetrahydrofolate cofactors

required for the methionine synthase reaction.

homocysteine

Apart from in the synthesis of methionine, S-adenosylmethionine is the only biological

________ group donor.

methyl

Tyrosine is the precursor of serotonin which has a number of roles in the nervous system.

FALSE

The catecholamine neurotransmitters are derived from ________.

tyrosine