Question 1

In regarding the degradation of heme

Accepted Answer

A)   heme is converted first to bilirubin, then to biliverdin, which is secreted in bile.
B)   the breakdown of bilirubin to biliverdin is accompanied by consumption of NADPH and production of NADP.
C)   the initial breakdown step is accomplished by heme oxygenase.
D)   all of the above.
E)   none of the above.F) C) and D)
G) C) and E)

Question 2

The major normal route of phenylalanine catabolism proceeds through

Accepted Answer

A)   phenylpyruvic acid.
B)   tyrosine.
C)   hydroxyphenyllactic acid.
D)   serotonin.
E)   homogentisic acid.F) C) and E)
G) A) and C)

Question 3

The three branched chain amino acids (valine, leucine and isoleucine)

Accepted Answer

A)   share a common enzyme for the oxidative decarboxylation of their alpha-keto analogues.
B)   share a common synthetic pathway in man.
C)   all give rise to the same end products to feed into the tricarboxylic acid cycle.
D)   cannot be transaminated.
E)   must be deaminated by L-amino acid oxidase.F) None of the above
G) B) and D)

Question 4

Which of the following statements concerning bilirubin is/are TRUE?

Accepted Answer

A)   Unconjugated bilirubin is bound to albumin in the serum.
B)   Obstruction of the bile duct may result in increases in serum of both direct and indirect bilirubin.
C)   Defective UDP-glucuronyl transferase may result in above normal values of indirect bilirubin in serum.
D)   A and B only are true.
E)   A, B, and C are true.F) B) and E)
G) C) and E)

Question 5

The naturally occurring porphyrins are the

Accepted Answer

A)   I and II isomers
B)   I and III isomers
C)   II and III isomers
D)   III and IX isomersE) C) and D)
F) B) and C)

Question 6

The rate-limiting reaction in urea production is that catalyzed by

Accepted Answer

A)   argininosuccinase.
B)   argininosuccinate synthetase.
C)   arginase.
D)   ornithine transcarbamoylase.
E)   carbamoyl phosphate synthetase.F) None of the above
G) B) and C) E

Question 7

A genetic disease characterized by accumulation of excess phenylalanine in the tissues, mental retardation, and excretion of phenylalanine metabolites in the urine is caused by a deficiency in

Accepted Answer

A)   phenylalanine transaminase.
B)   tyrosine transaminase.
C)   phenylalanine hydroxylase.
D)   homogentisic acid oxidase.
E)   phenylalanine decarboxylase.F) A) and B)
G) A) and C) C

Question 8

Conjugation of bilirubin occurs

Accepted Answer

A)   in the lungs.
B)   in the reticuloendothelial system.
C)   in erythrocytes.
D)   in the parenchymal cells of the liver.
E)   none of the above.F) A) and D)
G) None of the above

Question 9

The biosynthesis of tyrosine in normal humans requires which of the following amino acids in the diet?

Accepted Answer

A)   phenylalanine
B)   methionine
C)   histidine
D)   threonine
E)   leucineF) A) and E)
G) D) and E)

Question 10

In mammals, the methyl group of S-adenosylmethionine

Accepted Answer

A)   can be transferred to deoxyuridine monophosphate (dUMP)  to form deoxythymidine monophosphate.
B)   is transferred to putrescine to form higher polyamines.
C)   can react with tetrahydrofolate to form 5-methyl tetrahydrofolate.
D)   can react with malonyl CoA to form methylmalonyl CoA.
E)   is incorporated directly into cysteine via the trans-sulfuration pathway.F) C) and D)
G) A) and B)

Question 11

The immediate precursor of heme in its synthesis is

Accepted Answer

A)   protoporphyrin IX.
B)   coproporphyrinogen III.
C)   uroporphyrinogen III.
D)   porphobilinogen.
E)   bilirubin.F) A) and D)
G) B) and E)

Question 12

Pyridoxal phosphate acts as coenzyme in most

Accepted Answer

A)   transmethylation reactions.
B)   carbon dioxide fixation reactions.
C)   transamination reactions.
D)   kinase reactions.
E)   none of the above.F) A) and E)
G) A) and D)

Question 13

Which of the following statements about heme degradation is correct?

Accepted Answer

A)   A heme oxidase localized in the red blood cell catalyzes excision of the alpha-methene group yielding verdohemoglobin
B)   Conversion of biliverdin to bilirubin involves a 2-electron reduction of the biliverdin molecule.
C)   Direct bilirubin measured in the Van den Bergh test is mostly bilirubin diglucuronide.
D)   A and B are correct.
E)   B and C are correct.F) A) and D)
G) None of the above

Question 14

A deficiency in which ONE of the following enzymes would be most likely to cause hyperammonemia?

Accepted Answer

A)   Creatine kinase
B)   L-amino acid oxidase
C)   Serine transhydroxymethylase
D)   Carbamoyl phosphate synthetase I
E)   Phenylalanine hydroxylaseF) B) and E)
G) B) and C)

Question 15

Which compound is not a participant in the urea cycle?

Accepted Answer

A)   argininosuccinate
B)   ornithine
C)   ureidosuccinate
D)   citrulline
E)   carbamoyl phosphateF) None of the above
G) A) and E)

Question 16

The dietary requirement for nicotinic acid may be spared by an adequate amount of which one of the following amino acids?

Accepted Answer

A)   tryptophan
B)   glutamine
C)   histidine
D)   tyrosine
E)   phenylalanineF) A) and B)
G) A) and C)

Question 17

Which amino acid is the precursor of serotonin?

Accepted Answer

A)   Phenylalanine
B)   Tryptophan
C)   Tyrosine
D)   Glutamic acid
E)   ArginineF) A) and E)
G) B) and E)

Question 18

Which amino acid donates the carbon chain in the biosynthesis of cysteine?

Accepted Answer

A)   methionine
B)   cystine
C)   glycine
D)   serine
E)   half-cystineF) A) and E)
G) A) and D)

Question 19

Which statement about enzyme-catalyzed transamination is FALSE?

Accepted Answer

A)   The equilibrium constant is approximately 1.
B)   The reaction involves a Schiff base intermediate.
C)   The reaction is important in the conversion of amino acid nitrogen to urea.
D)   NAD+ or NADP+ is required.
E)   There is no transient release of ammonia.F) All of the above
G) B) and C) D

Question 20

Tetrahydrobiopterin is a cofactor required for which one of the following conversions?

Accepted Answer

A)   Dihydrofolate -> tetrahydrofolate
B)   Phenylalanine -> tyrosine
C)   Methionine -> cysteine
D)   Phenylalanine -> phenylpyruvate
E)   None of the above.F) A) and B)
G) B) and D)

Exam 19: Amino Acid Metabolism

In regarding the degradation of heme

Correct AnswerverifiedShow Answer

The major normal route of phenylalanine catabolism proceeds through

Correct AnswerverifiedShow Answer

The three branched chain amino acids (valine, leucine and isoleucine)

Correct AnswerverifiedShow Answer

Which of the following statements concerning bilirubin is/are TRUE?

Correct AnswerverifiedShow Answer

The naturally occurring porphyrins are the

Correct AnswerverifiedShow Answer

The rate-limiting reaction in urea production is that catalyzed by

Correct AnswerverifiedE

A genetic disease characterized by accumulation of excess phenylalanine in the tissues, mental retardation, and excretion of phenylalanine metabolites in the urine is caused by a deficiency in

Correct AnswerverifiedC

Conjugation of bilirubin occurs

Correct AnswerverifiedShow Answer

The biosynthesis of tyrosine in normal humans requires which of the following amino acids in the diet?

Correct AnswerverifiedShow Answer

In mammals, the methyl group of S-adenosylmethionine

Correct AnswerverifiedShow Answer

The immediate precursor of heme in its synthesis is

Correct AnswerverifiedShow Answer

Pyridoxal phosphate acts as coenzyme in most

Correct AnswerverifiedShow Answer

Which of the following statements about heme degradation is correct?

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A deficiency in which ONE of the following enzymes would be most likely to cause hyperammonemia?

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Which compound is not a participant in the urea cycle?

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The dietary requirement for nicotinic acid may be spared by an adequate amount of which one of the following amino acids?

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Which amino acid is the precursor of serotonin?

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Which amino acid donates the carbon chain in the biosynthesis of cysteine?

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Which statement about enzyme-catalyzed transamination is FALSE?

Correct AnswerverifiedD

Tetrahydrobiopterin is a cofactor required for which one of the following conversions?

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E

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C

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D

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