Question 1

The first nucleotide product in the de novo biosynthetic pathway of purines is

Accepted Answer

A)  AMP.
B)  GMP.
C)  IMP.
D)  XMP.E) A) and B)
F) A) and C)

Question 2

Which catalytic site is not contained in the eukaryotic multifunctional protein dihydroorotate synthase?

Accepted Answer

A)  Orotate phosphoribosyltransferase.
B)  ATCase.
C)  Carbamoyl phosphate synthetase II.
D)  Dihydroorotase.E) A) and B)
F) A) and C)

Question 3

The pyrimidine ring system is shown below.What is the source of the N-3 during the de novo biosynthesis of pyrimidines?

Accepted Answer

A)  Ammonia.
B)  Glutamine.
C)  Arginine.
D)  Urea.E) C) and D)
F) A) and D)

Question 4

Virtually all organisms and tissues can synthesize nucleotides.

Accepted Answer

A) True 
 B)False

Question 5

Which enzyme catalyzes the step in purine nucleotide biosynthesis that is the principal site of regulation for the pathway?

Accepted Answer

A)  Adenylsuccinate lyase.
B)  OPM decarboxylase.
C)  IMP cyclohydrolase.
D)  Glutamine-PRPP amidotransferase.E) B) and D)
F) C) and D)

Question 6

During de novo biosynthesis of the purine nucleotides,the purine ring is first formed as a free base before being attached to the ribose 5-phosphate moiety.

Accepted Answer

A) True 
 B)False

Question 7

The pathway for the synthesis of IMP releases considerable energy and is an important source of ATP.

Accepted Answer

A) True 
 B)False

Question 8

Humans and other terrestrial organisms lack the enzyme urease which,if present,would cause a toxic level of ammonia.

Accepted Answer

A) True 
 B)False

Question 9

Although dUTP can be synthesized from UDP and ATP,it is not accidentally incorporated into DNA in place of ________ because it is rapidly hydrolyzed

Accepted Answer

A)  dATP
B)  dGTP
C)  dCTP
D)  dTTPE) A) and C)
F) None of the above

Question 10

Which is not a direct precursor of pyrimidines in their de novo biosynthesis?

Accepted Answer

A)  HCO3-.
B)  Glutamine.
C)  Glycine.
D)  Aspartate.E) None of the above
F) A) and B)

Question 11

dUTP is not a direct precursor of dTTP because ________.

Accepted Answer

A)  there are no enzymes for this reaction
B)  dUTP controls DNA synthesis
C)  it could possibly be incorporated into DNA
D)  All of the aboveE) All of the above
F) None of the above

Question 12

5-methylcytidine is a common modified base in mammalian DNA that plays roles in ________.

Accepted Answer

A)  restriction endonucleases
B)  regulation of transcription
C)  chromatin assembly
D)  both B and CE) A) and B)
F) A) and C)

Question 13

The purine ring system is shown below.What is the source of the C-6 atom during de novo biosynthesis of purines?

Accepted Answer

A)  Carbon dioxide.
B)  Tetrahydrofolate.
C)  Carbamoyl phosphate.
D)  Glycine.E) None of the above
F) A) and D)

Question 14

In pyrimidine nucleotide biosynthesis orotate is the molecule that displaces the pyrophosphate group on PRPP.

Accepted Answer

A) True 
 B)False

Question 15

Channeling is an important process in the biosynthesis of pyrimidine nucleotides in mammals.

Accepted Answer

A) True 
 B)False

Question 16

Allopurinol may be used to treat gout due to an excess of uric acid production because it can be converted to oxypurinol by ________,and oxypurinol strongly inhibits ________.

Accepted Answer

A)  xanthine dehydrogenase;xanthine dehydrogenase
B)  xanthine dehydrogenase;sodium urate
C)  urease;xanthine dehydrogenase
D)  xanthine dehydrogenase;urease
E)  urease;ureaseF) B) and D)
G) A) and C)

Question 17

Which are purines?

Accepted Answer

A)  Adenine and thymine.
B)  Guanine and adenine.
C)  Cytosine and thymine.
D)  Uracil and guanine.E) All of the above
F) C) and D)

Question 18

The major end product of purine degradation in humans is

Accepted Answer

A)  allantoin.
B)  guanine.
C)  urate.
D)  ammonia.E) B) and C)
F) All of the above

Question 19

Carbamoyl phosphate synthetase I is located in the ________ in eukaryotes and uses ________ as a nitrogen source.

Accepted Answer

A)  mitochondria;glutamine
B)  mitochondria;ammonia
C)  cytosol;glutamine
D)  cytosol;ammoniaE) A) and B)
F) B) and C)

Question 20

PRPP synthetase is inhibited by several purine ribonucleotides but only at concentrations lower than those usually found in the cell so there remains a supply for other cell reactions.

Accepted Answer

A) True 
 B)False

Exam 18: Nucleotide Metabolism

Channeling is an important process in the biosynthesis of pyrimidine nucleotides in mammals.

Correct AnswerverifiedShow Answer

Although dUTP can be synthesized from UDP and ATP,it is not accidentally incorporated into DNA in place of ________ because it is rapidly hydrolyzed

Correct AnswerverifiedShow Answer

dUTP is not a direct precursor of dTTP because ________.

Correct AnswerverifiedShow Answer

During de novo biosynthesis of the purine nucleotides,the purine ring is first formed as a free base before being attached to the ribose 5-phosphate moiety.

Correct AnswerverifiedShow Answer

Humans and other terrestrial organisms lack the enzyme urease which,if present,would cause a toxic level of ammonia.

Correct AnswerverifiedShow Answer

Which catalytic site is not contained in the eukaryotic multifunctional protein dihydroorotate synthase?

Correct AnswerverifiedShow Answer

The first nucleotide product in the de novo biosynthetic pathway of purines is

Correct AnswerverifiedShow Answer

The purine ring system is shown below.What is the source of the C-6 atom during de novo biosynthesis of purines?

Correct AnswerverifiedShow Answer

Allopurinol may be used to treat gout due to an excess of uric acid production because it can be converted to oxypurinol by ________,and oxypurinol strongly inhibits ________.

Correct AnswerverifiedShow Answer

The major end product of purine degradation in humans is

Correct AnswerverifiedShow Answer

PRPP synthetase is inhibited by several purine ribonucleotides but only at concentrations lower than those usually found in the cell so there remains a supply for other cell reactions.

Correct AnswerverifiedShow Answer

Carbamoyl phosphate synthetase I is located in the ________ in eukaryotes and uses ________ as a nitrogen source.

Correct AnswerverifiedShow Answer

Which enzyme catalyzes the step in purine nucleotide biosynthesis that is the principal site of regulation for the pathway?

Correct AnswerverifiedShow Answer

The pathway for the synthesis of IMP releases considerable energy and is an important source of ATP.

Correct AnswerverifiedShow Answer

Which are purines?

Correct AnswerverifiedShow Answer

Which is not a direct precursor of pyrimidines in their de novo biosynthesis?

Correct AnswerverifiedShow Answer

Virtually all organisms and tissues can synthesize nucleotides.

Correct AnswerverifiedShow Answer

In pyrimidine nucleotide biosynthesis orotate is the molecule that displaces the pyrophosphate group on PRPP.

Correct AnswerverifiedShow Answer

The pyrimidine ring system is shown below.What is the source of the N-3 during the de novo biosynthesis of pyrimidines?

Correct AnswerverifiedShow Answer

5-methylcytidine is a common modified base in mammalian DNA that plays roles in ________.

Correct AnswerverifiedShow Answer

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Allopurinol may be used to treat gout due to an excess of uric acid production because it can be converted to oxypurinol by ,and oxypurinol strongly inhibits .

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Carbamoyl phosphate synthetase I is located in the in eukaryotes and uses as a nitrogen source.

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