Deck 18: Amino Acid Oxidation and the Production of Urea

Question 1

Conversion of ammonia to carbamoyl phosphate in mitochondria consumes how many ATP equivalents?

A) none
B) one
C) two
D) three

Answer 1

C

Question 2

Which reaction associated with the urea cycle occurs in the cytosol?

A) the synthesis of carbamoyl phosphate
B) the synthesis of citrulline
C) the synthesis of arginosuccinate
D) the synthesis of both carbamoyl phosphate and citrulline
E) the synthesis of both citrulline and arginosuccinate

Answer 2

C

Question 3

Carbamoyl phosphate synthase I is allosterically activated by what molecule?

A) glutamate
B) arginine
C) N-acetylglutamate
D) carbamoyl phosphate
E) acetyl-CoA

Answer 3

C

Question 4

Which statement is FALSE regarding pepsin?

A) This enzyme is activated by irreversible covalent modification.
B) This enzyme is classified as a hydrolase.
C) This enzyme is highly active at neutral pH.
D) This enzyme is secreted in response to protein ingestion.
E) This enzyme has a specificity for cleavage at aromatic amino acids.

Question 5

Which amino acid can be imported into mitochondria from the cytosol in liver cells?

A) glutamine
B) glutamate
C) ornithine
D) All of the answers are correct.
E) None of the answers is correct.

Question 6

Which cofactor is typically required in transamination reactions?

A) pyridoxal-phosphate
B) coenzyme Q
C) biotin
D) thiamin pyrophosphate
E) nicotinamide adenine dinucleotide

Question 7

Nitrogen from protein is eliminated as what compound in animals?

A) ammonia
B) urea
C) pyrimidine
D) both ammonia and urea
E) both urea and pyrimidine

Question 8

Which statement is FALSE for uric acid?

A) This compound is produced in humans as a result of high-protein diets.
B) This compound is the major means of nitrogen elimination in birds.
C) This compound is a purine base.
D) This compound is a product of both protein and nucleic acid catabolism.
E) None of the statements is false.

Question 9

Which amino acid can be considered to be both glucogenic and ketogenic?

A) threonine
B) aspartate
C) leucine
D) isoleucine
E) both threonine and isoleucine

Question 10

Which hormone is triggered by the entry of acidic stomach content into the intestine?

A) gastrin
B) insulin
C) cholecystokinin
D) secretin

Question 11

Deamination of most amino acids in the liver is accompanied by the conversion of:

A) pyruvate into alanine.
B) glutamate into glutamine.
C) $\alpha$ -ketoglutarate into glutamate.
D) nitrogen into urea.
E) oxaloacetate into aspartate.

Question 12

Which amino acid is used to transport nitrogen to the liver?

A) alanine
B) asparagine
C) glutamine
D) glutamate
E) both alanine and glutamine

Question 13

Which statement is TRUE regarding glutamine synthetase?

A) This enzyme is classified as a ligase.
B) An intermediate in the reaction catalyzed by this enzyme is an acyl phosphate.
C) This enzyme catalyzes a transamination reaction.
D) This enzyme is classified as a ligase, and an intermediate in the reaction catalyzed by this enzyme is an acyl phosphate.
E) This enzyme is classified as a ligase and catalyzes a transamination reaction.

Question 14

Which hormone is triggered by the entry of protein into the stomach?

A) gastrin
B) insulin
C) cholecystokinin
D) secretin

Question 15

In which pair of compounds is the second molecule produced by the deamination of the first molecule?

A) aspartic acid and oxaloacetate
B) glutamine and glutamate
C) alanine and pyruvate
D) All of the answers are correct.
E) None of the answers is correct.

Question 16

What processes are associated with the glucose-alanine cycle?

A) Gluconeogenesis in the liver
B) Glutamate synthesis in both muscle and the liver
C) Glucose export from the liver
D) All of the answers are correct.
E) None of the answers is correct.

Question 17

A possible product of isoleucine catabolism is:

A) acetyl-CoA.
B) succinyl-CoA.
C) conversion to $\alpha$ -keto isoleucine ( $\alpha$ -keto- $\beta$ -methylvalerate).
D) All of the answers are correct.
E) None of the answers is correct.

Question 18

Which statement is FALSE regarding pyridoxal phosphate?

A) This prosthetic group is critical in aminotransferase reactions.
B) This cofactor can form covalent bonds to lysine residues enzyme.
C) This cofactor can form covalent bonds to some intermediates.
D) This cofactor carries both positive and negative formal charges.
E) None of the statements is false.

Question 19

Which reaction is a hydrolysis reaction?

A) the conversion of arginine into urea and ornithine by arginase
B) the conversion of glutamine into glutamate by glutamase
C) the conversion of tyrosine into phenylalanine by phenylalanine hydroxylase
D) both the conversion of the arginine into urea and ornithine by arginase and the conversion of glutamine into glutamate by glutamase
E) both the conversion of glutamine into glutamate by glutamase and the conversion of tyrosine into phenylalanine by phenylalanine hydroxylase

Question 20

What enzyme classes are responsible for interconverting glutamate and $\alpha$ -ketoglutarate?

A) hydrolases
B) transferases
C) ligases
D) All of the answers are correct.
E) None of the answers is correct.

Question 21

Which amino acid enters the citric acid cycle as $\alpha$ -ketoglutarate during their catabolism?

A) proline
B) threonine
C) aspartate
D) leucine
E) None of the answers is correct.

Question 22

If ¹⁵N-labeled glutamate is introduced into liver cells, what compounds in the urea cycle will NOT be rapidly labeled with the nitrogen?

A) ornithine
B) aspartate
C) arginine
D) urea
E) both ornithine and aspartate

Question 23

What enzyme converts arginine into urea and ornithine?

A) arginase
B) urease
C) ornithine synthase
D) arginosuccinase

Question 24

Conversion of serine into glycine requires which cofactor?

A) tetrahydrofolate
B) pyridoxal 5' phosphate
C) NADH
D) All of the answers are correct.
E) None of the answers is correct.

Question 25

Which statement is TRUE regarding tyrosine catabolism?

A) The first step in catabolism of tyrosine is reduction to phenylalanine.
B) Tyrosine can be considered solely glucogenic.
C) Atoms from tyrosine's sidechain enter the citric acid cycle as fumarate.
D) All of the statements are true.
E) None of the statements is true.

Question 26

Which compound is NOT transported across the inner mitochondrial membrane as part of either the urea cycle and aspartate-arginosuccinate shunt?

A) fumarate
B) aspartate
C) ornithine
D) citrulline
E) neither fumarate nor citrulline

Question 27

Which product is created during the conversion of threonine into glycine during amino acid catabolism?

A) acetyl-CoA
B) water
C) NADH
D) both acetyl-CoA and NADH
E) both water and NADH

Question 28

Which compound can be described as glucogenic?

A) leucine
B) isoleucine
C) lysine
D) All of the answers are correct.
E) None of the answers is correct.

Question 29

Catabolism of which substance can enter the citric acid cycle as succinyl-CoA?

A) threonine
B) odd-numbered fatty acids
C) methionine
D) All of the answers are correct.
E) None of the answers is correct.

Question 30

Phenylketoneuria is associated with disorders in the catabolism of which amino acid?

A) phenylalanine
B) tyrosine
C) tryptophan
D) histidine

Question 31

If ¹⁴C-labeled glutamate is introduced into liver cells, what compounds in the urea cycle will be rapidly labeled with the carbon?

A) ornithine
B) aspartate
C) arginine
D) urea
E) None of the answers is correct.

Question 32

Which compound is used in single-carbon transfer reactions?

A) S-adenosyl methionine
B) tetrahydrofolate
C) biotin
D) All of the answers are correct.
E) None of the answers is correct.

Question 33

Which statement is FALSE regarding ketogenic and glucogenic amino acids?

A) Glucogenic amino acids cannot be used to make ketone bodies.
B) Ketogenic amino acids can be used to synthesize fatty acids.
C) Leucine and Isoleucine are both exclusively ketogenic amino acids.
D) Both valine and threonine catabolism produce succinyl-CoA.

Question 34

Which statement is TRUE regarding the conversion of arginine to ornithine in the urea cycle?

A) The enzyme catalyzing this reaction is a hydrolase.
B) This enzyme-catalyzed reaction occurs in the matrix.
C) One of the products of this reaction is fumarate.
D) The enzyme catalyzing this reaction is a ligase.
E) The enzyme catalyzing this reaction is a hydrolase, and the reaction occurs in a matrix.

Question 35

Which compound is NOT an intermediate in the conversion of alanine's carbon skeleton into that of aspartate?

A) acetyl-CoA
B) pyruvate
C) lactate
D) oxaloacetate
E) neither acetyl-CoA nor lactate

Question 36

Serotonin is produced from the metabolism of which amino acid?

A) valine
B) serine
C) cysteine
D) tyrosine
E) tryptophan

Question 37

Methionine synthase uses what substrates to synthesize methionine?

A) cysteine
B) S-adenosyl methionine
C) ATP
D) homocysteine

Question 38

Which compound can be described as exclusively ketogenic?

A) leucine
B) isoleucine
C) lysine
D) both leucine and lysine
E) both isoleucine and lysine

Question 39

Which statement is TRUE regarding lysine?

A) This is a nonessential amino acid.
B) Catabolism of lysine shares multiple steps with that of tryptophan.
C) Carbons of lysine catabolism enter the citric acid cycle at succinyl-CoA.
D) Lysine is both glucogenic and ketogenic enzyme.

Question 40

Which amino acid is catabolized to both succinyl-CoA and acetyl-CoA?

A) leucine
B) isoleucine
C) lysine
D) valine
E) both isoleucine and valine

Question 41

The conversion of glutamate to an $\alpha$ -keto acid 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.

Question 42

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

Question 43

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

Question 44

Which reaction involving an amino acid CANNOT be catalyzed via a PLP-dependent mechanism?

A) hydrolysis
B) decarboxylation
C) racemization
D) transamination
E) transimination

Question 45

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).

Question 46

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

A) adenine
B) aspartate
C) creatine
D) glutamate
E) ornithine

Question 47

The coenzyme required for all transaminations is derived from:

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

Question 48

Which statement 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) $\alpha$ -Ketoglutarate is produced from an amino acid.

Question 49

Transamination from alanine to $\alpha$ -ketoglutarate requires the coenzyme:

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

Question 50

Which statement 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.

Question 51

Which amino acid is essential for humans?

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

Question 52

Which compound is NOT a protease that acts in the small intestine?

A) chymotrypsin
B) elastase
C) enteropeptidase
D) secretin
E) trypsin

Question 53

Which compound 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

Question 54

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

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

Question 55

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.

Question 56

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).

Question 57

Which statement is TRUE regarding the branched-chain $\alpha$ -keto acid dehydrogenase complex?

A) This enzyme is activated by phosphorylation.
B) This enzyme catalyzes a reaction homologous to succinate dehydrogenase.
C) This enzyme catalyzes an oxidative decarboxylation.
D) All of the statements are true.
E) None of the statements is true.

Question 58

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

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

Question 59

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

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

Question 60

Under which circumstances are amino acids NOT metabolized via oxidative degradation?

A) starvation
B) plants growing in nutrient-rich soils
C) normal protein turnover
D) a diet rich in proteins
E) uncontrolled diabetes

Question 61

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.

Question 62

Alanine aminotransferase catalyzes the transamination of alanine and $\alpha$ -ketoglutarate to pyruvate and glutamate, while aspartate transaminase converts aspartate and $\alpha$ -ketoglutarate to oxaloacetate and glutamate. If you have a 50.0-mL reaction volume containing 0.100 M alanine, $\alpha$ -ketoglutarate, glutamate, and oxaloacetate, what will the equilibrium concentration of aspartate be? Assume an equilibrium constant of 1.0 for both enzyme-catalyzed reactions.

Question 63

Define zymogen and describe the role of one zymogen in protein digestion.

Question 64

_____ is NOT a form of the most oxidized state of tetrahydrofolate (THF).

A) N¹⁰-formyl THF
B) N⁵N¹⁰-methenyl THF
C) N⁵N¹⁰-methylene THF
D) N⁵-formyl THF
E) N⁵-formimino THF

Question 65

Describe (briefly) the role of (a) gastrin, (b) pepsinogen, (c) cholecystokinin, and (d) enteropeptidase in protein digestion.

Question 66

The E3 subunit of pyruvate dehydrogenase, $\alpha$ -ketoglutarate dehydrogenase and the branched-chain $\alpha$ -keto acid dehydrogenase complex is identical in each multi-enzyme complex. What reaction is catalyzed by this subunit, and why it does it make sense that it is common while E1 and E2 are not?

Question 67

Outline two paths by which ¹⁴N-labeled glutamate can lead to labeled products in the urea cycle.

Question 68

Which amino acids are both ketogenic and glucogenic?

Question 69

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.

Question 70

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

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

Question 71

The bacterium responsible for gastric ulcers, Helicobacter pylori, survives the acidic pH of the stomach surprisingly well. It does so in part by synthesizing and excreting large amounts of the enzyme urease, which hydrolyzes urea to bicarbonate and ammonia. Explain how these reaction products lead to a less acidic environment for H. pylori.

Question 72

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.

Question 73

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

A) fumarate.
B) pyruvate.
C) succinate.
D) $\alpha$ -ketoglutarate.
E) None of the answers is correct.

Question 74

Which amino acids are converted to -ketoglutarate?

Question 75

If a person's urine contains unusually high concentrations of urea, which diet 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

Question 76

The amino acids leucine, valine, and isoleucine are preferentially catabolized in muscle tissue, while other amino acids are catabolized primarily in the liver. Given the characteristics of these amino acids, why might this be advantageous? Where in the cell would you expect them to be catabolized?

Question 77

In the treatment of diabetes, insulin is given intravenously. Why can't this hormone, a small protein, be taken orally?

Question 78

Both glutamine and alanine transport nitrogen in the bloodstream. Why might be it be considered an advantage to transport glutamine instead of alanine?

Question 79

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

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

Question 80

Transamination reactions are catalyzed by a family of enzymes, all of which require _____ as a coenzyme. In the first step of a transamination, the coenzyme in the aldehyde form condenses with the _____ group of an amino acid to form a(n) _____.