Chapter 18

Question 1

Which of these is not a protease that acts in the small intestine?

A) Chymotrypsin
B) Elastase
C) Enteropeptidase
D) Secretin
E) Trypsin

Answer 1

D) Secretin

Question 2

In the digestion of protein that occurs in the small intestine, which enzyme is critical in the activation
of zymogens?

A) Enteropeptidase
B) Hexokinase
C) Papain
D) Pepsin
E) Secretin

Answer 2

A) Enteropeptidase

Question 3

Which of the following is a zymogen that can be converted to an endopeptidase that hydrolyzes
peptide bonds adjacent to Lys and Arg residues?

A) Chymotrypsinogen
B) Pepsin
C) Pepsinogen
D) Trypsin
E) Trypsinogen

Answer 3

E) Trypsinogen

Question 4

In amino acid catabolism, the first reaction for many amino acids is a(n):

A) decarboxylation requiring thiamine pyrophosphate (TPP).
B) hydroxylation requiring NADPH and O2.
C) oxidative deamination requiring NAD+
D) reduction requiring pyridoxal phosphate (PLP).
E) transamination requiring pyridoxal phosphate (PLP).

Answer 4

E) transamination requiring pyridoxal phosphate (PLP).

Question 5

The coenzyme required for all transaminations is derived from:

A) niacin.
B) pyridoxine (vitamin B6).
C) riboflavin.
D) thiamin.
E) vitamin B12.

Answer 5

B) pyridoxine (vitamin B6).

Question 6

The coenzyme involved in a transaminase reaction is:

A) biotin phosphate.
B) lipoic acid.
C) nicotinamide adenine dinucleotide phosphate (NADP+).
D) pyridoxal phosphate (PLP).
E) thiamine pyrophosphate (TPP).

Answer 6

D) pyridoxal phosphate (PLP).

Question 7

Transamination from alanine to a-ketoglutarate requires the coenzyme:

A) biotin.
B) NADH.
C) No coenzyme is involved.
D) pyridoxal phosphate (PLP).
E) thiamine pyrophosphate (TPP)

Answer 7

D) pyridoxal phosphate (PLP).

Question 8

Pyridoxal phosphate is a cofactor in this class of reactions:

A) acetylation.
B) desulfuration.
C) methylation.
D) reduction.
E) transamination.

Answer 8

E) transamination.

Question 9

Which of the following is not true of the reaction catalyzed by glutamate dehydrogenase?

A) It is similar to transamination in that it involves the coenzyme pyridoxal phosphate (PLP).
B) NH4
+ is produced.
C) The enzyme can use either NAD+ or NADP+ as a cofactor.
D) The enzyme is glutamate-specific, but the reaction is involved in oxidizing other amino acids.
E) a-Ketoglutarate is produced from an amino acid.

Answer 9

A) It is similar to transamination in that it involves the coenzyme pyridoxal phosphate (PLP).

Question 10

Glutamate is metabolically converted to a-ketoglutarate and NH4+ by a process described as:

A) deamination.
B) hydrolysis.
C) oxidative deamination.
D) reductive deamination.
E) transamination.

Answer 10

C) oxidative deamination.

Question 11

The conversion of glutamate to an a-ketoacid and NH4+ :

A) does not require any cofactors.
B) is a reductive deamination.
C) is accompanied by ATP hydrolysis catalyzed by the same enzyme.
D) is catalyzed by glutamate dehydrogenase.
E) requires ATP.

Answer 11

D) is catalyzed by glutamate dehydrogenase.

Question 12

Which of the following conversions require more than one step?

1. Alanine ® pyruvate
2. Aspartate ® oxaloacetate
3. Glutamate ® a-ketoglutarate
4. Phenylalanine ® hydroxyphenylpyruvate
5. Proline ® glutamate

A) 1 and 4
B) 1, 2, and 4
C) 1, 3, and 5
D) 2, 4, and 5
E) 4 and 5

Answer 12

E) 4 and 5

Question 13

Urea synthesis in mammals takes place primarily in tissues of the:

A) brain.
B) kidney.
C) liver.
D) skeletal muscle.
E) small intestine.

Answer 13

C) liver.

Question 14

Which substance is not involved in the production of urea from NH4+ via the urea cycle?

A) Aspartate
B) ATP
C) Carbamoyl phosphate
D) Malate
E) Ornithine

Answer 14

D) Malate

Question 15

Which of these directly donates a nitrogen atom for the formation of urea during the urea cycle?

A) Adenine
B) Aspartate
C) Creatine
D) Glutamate
E) Ornithine

Answer 15

B) Aspartate

Question 16

Conversion of ornithine to citrulline is a step in the synthesis of:

A) aspartate.
B) carnitine.
C) pyruvate.
D) tyrosine.
E) urea.

Answer 16

E) urea.

Question 17

In the urea cycle, ornithine transcarbamoylase catalyzes:

A) cleavage of urea to ammonia.
B) formation of citrulline from ornithine and another reactant.
C) formation of ornithine from citrulline and another reactant.
D) formation of urea from arginine.
E) transamination of arginine.

Answer 17

B) formation of citrulline from ornithine and another reactant.

Question 18

Which of the following statements is false in reference to the mammalian synthesis of urea?

A) Krebs was a major contributor to the elucidation of the pathway involved.
B) The amino acid arginine is the immediate precursor to urea.
C) The carbon atom of urea is derived from mitochondrial HCO3–
D) The precursor to one of the nitrogens of urea is aspartate.
E) The process of urea production is an energy-yielding series of reactions.

Answer 18

E) The process of urea production is an energy-yielding series of reactions.

Question 19

Which of the following amino acids are essential for humans?

A) alanine
B) aspartic acid
C) asparagine
D) serine
E) threonine

Answer 19

E) threonine

Question 20

If a person’s urine contains unusually high concentrations of urea, which one of the following diets has he or she probably been eating recently?

A) High carbohydrate, very low protein
B) Very high carbohydrate, no protein, no fat
C) Very very high fat, high carbohydrate, no protein
D) Very high fat, very low protein
E) Very low carbohydrate, very high protein

Answer 20

E) Very low carbohydrate, very high protein

Question 21

Which of these amino acids can be directly converted into a citric acid cycle intermediate by transamination?

A) glutamic acid
B) serine
C) threonine
D) tyrosine
E) proline

Answer 21

A) glutamic acid

Question 22

Which of these amino acids are both ketogenic and glucogenic?

1. Isoleucine
2. Valine
3. Histidine
4. Arginine
5. Tyrosine

A) 1 and 5
B) 1, 3, and 5
C) 2 and 4
D) 2, 3, and 4
E) 2, 4, and 5

Answer 22

A) 1 and 5

Question 23

Tetrahydrofolate (THF) and its derivatives shuttle between different substrates.

A) electrons
B) H+
C) acyl groups
D) one carbon units
E) NH2 groups

Answer 23

D) one carbon units

Question 24

The amino acids serine, alanine, and cysteine can be catabolized to yield:

A) fumarate.
B) pyruvate.
C) succinate.
D) a-ketoglutarate.
E) none of the above.

Answer 24

B) pyruvate.

Question 25

Serine or cysteine may enter the citric acid cycle as acetyl-CoA after conversion to:

A) oxaloacetate.
B) propionate.
C) pyruvate.
D) succinate.
E) succinyl-CoA.

Answer 25

C) pyruvate.

Question 26

The human genetic disease phenylketonuria (PKU) can result from:

A) deficiency of protein in the diet.
B) inability to catabolize ketone bodies.
C) inability to convert phenylalanine to tyrosine.
D) inability to synthesize phenylalanine.
E) production of enzymes containing no phenylalanine

Answer 26

C) inability to convert phenylalanine to tyrosine.

Question 27

In the human genetic disease maple syrup urine disease, the metabolic defect involves:

A) a deficiency of the vitamin niacin.
B) oxidative decarboxylation.
C) synthesis of branched chain amino acids.
D) transamination of an amino acid.
E) uptake of branched chain amino acids into liver.

Answer 27

B) oxidative decarboxylation.