Deck 13: Nucleotide Deoxynucleotide Metabolism

Question 1

In purine biosynthesis, amination of PRPP and FGAR, through catalysis by amidophosphoribosyl transferase and formylglycinamide ribonucleotide synthetase, respectively, requires the amino acid

A) glutamate
B) glycine
C) glutamine
D) alanine
E) aspartate

Answer 1

glutamine

Question 2

IMP synthesis from ribose-5-phosphate requires ___ ATP hydrolyses.

A) 2
B) 4
C) 6
D) 8
E) 10

Answer 2

6

Question 3

What coenzyme is used when inosine monophosphate is oxidized to xanthosine monophosphate?

A) NADPH
B) NADP⁺
C) NADH
D) NAD⁺
E) FAD

Answer 3

NAD⁺

Question 4

In Lesch-Nyhan syndrome, ___ is not salvaged, so is metabolized to uric acid, which accumulates in tissues.

A) guanine
B) adenine
C) thymidine
D) Both guanine and adenine
E) All of the above

Question 5

____ is released as adenylosuccinate lyase catalyzes the conversion of adenylosuccinate to AMP.

A) glutamine
B) glutamate
C) aspartate
D) PRPP
E) fumarate

Question 6

Which of the following amino acids is a source of both carbon and nitrogen for IMP?

A) Glu
B) Gln
C) Gly
D) Asp
E) Asn

Question 7

The precursor to AMP and GMP is ______.

Question 8

The conversion of IMP to AMP requires _____; the conversion of IMP to GMP requires _____.

A) Gln; Glu
B) Asp; Gln
C) Asn; Asp
D) Glu; Asn
E) Asp; Glu

Question 9

The energy for the conversion of IMP to GMP is supplied by _____.

A) ATP
B) CTP
C) GTP
D) TTP
E) UTP

Question 10

The following is the structure for acyclovir, an antiviral drug:
Similar to methotrexate and aminopterin, acyclovir is a(n) ______________, substituting for the deoxynucleotide ______________ during DNA synthesis.

Question 11

Which of the following steps in purine biosynthesis are regulated by feedback inhibition by ADP and GDP?
I. ribose-5-phosphate $\rightarrow$ PRPP
II. PRPP $\rightarrow$ 5-phosphoribosame
III. glycine ribonucleotide $\rightarrow$ formylglycinamide ribonucleotide
IV. FAICAR $\rightarrow$ IMP
V. IMP $\rightarrow$ adenylosuccinate

A) I only
B) I and V only
C) II, III, V
D) I and II
E) IV and V

Question 12

The common intermediate of purines AMP and GMP is __________, while the common intermediate of the pyrimidines cytosine, thymidine and uracil is ______.

Question 13

Dihydroorotate is synthesized from

A) glycine and carbamoyl phosphate.
B) arginine and carbamoyl phosphate.
C) aspartate and carbamoyl phosphate.
D) aspartate and glutamine.
E) asparagine and glutamine.

Question 14

Which of the following is correct regarding pyrimidine synthesis?

A)
B)
C)
D) A and C
E) None of the above

Question 15

What step is common to both purine and pyrimidine synthesis?

A) conversion of IMP to adenylosuccinate for AMP production
B) conversion of IMP to xanthosine monophosphate for GMP production
C) conversion of ribose-5-phosphate to 5-phosphoribosyl pyrophosphate
D) conversion of UTP to CTP

Question 16

Which of the following amino acids is a source of both carbon and nitrogen for UMP?

A) Glu
B) Gln
C) Gly
D) Asp
E) Asn

Question 17

Regulation of pyrimidine de novo synthesis in mammals is through allosteric control by

A) aspartate transcarbamoylase (ATCase)
B) OMP decarboxylase
C) dihydroorotase dehydrogenase
D) hypoxanthine-guanine phosphoribosyl transferase (HGPRTase)
E) ribose phosphate pyrophosphokinase

Question 18

In the pyrimidine salvage pathway, cytidine is first deaminated to

A) uridine
B) UMP
C) thymine
D) hypoxanthine
E) PRPP

Question 19

What enzyme is responsible for the conversion of nucleotides to deoxynucleotides?

A) ribonucleotide deoxidase
B) ribonucleotide dehydratase
C) ribonucleotide dehydrogenase
D) ribonucleotide oxidase
E) ribonucleotide reductase

Question 20

In the mechanism of ribonucleotide reductase, a _____ is generated at C3' to stabilize the _____ that is formed at C2'.

A) radical; carbocation
B) radical; carbanion
C) carbocation; radical
D) carbanion; radical
E) carbanion; carbocation

Question 21

What molecule is used to reduce ribonucleotide reductase back to its catalytically active state?

A) NADH
B) NADPH
C) thioredoxin
D) ferredoxin
E) FADH₂

Question 22

Ribonucleotide reductase relies on cofactors

A) Fe or Mn
B) Mn or Mg
C) Cu or Mg
D) Cu
E) None of the above

Question 23

Active site ___ are important to carbocation mechanism of ribonucleotide reductase

A) serines
B) aspartic acids
C) cysteines
D) NAD+ coenzymes
E) glutamines

Question 24

Which of the following are needed to regenerate the reduced form of ribonucleotide reductase?
I. glutredoxin disulfide
II. reduced glutathiones
III. disulfide thioredoxin
IV. FADH2

A) I and II
B) III and IV
C) II and IV
D) I, II and IV
E) All of the above

Question 25

At its allosteric site, ribonucleotide reductase is

A) inhibited by ATP and stimulated by dATP
B) inhibited by dATP and stimulated by ATP
C) inhibited by both ATP and dATP
D) stimulated by both ATP and dATP

Question 26

Important to balancing deoxynucleotide concentrations is control of the enzyme ____.

A) thymidylate synthase
B) ribonucleotide reductase
C) thioredoxin reductase
D) tetrahydrofolate reductase
E) ribose phosphate pyrophosphokinase

Question 27

Having both regulatory and catalytic subunits, ribonucleotide reductase undergoes ___ control

Question 28

The substrates of ribonucleotide reductase are

A) nucleotides
B) nucleotide monophosphates
C) nucleotide diphosphates
D) nucleotide triphosphates
E) deoxynucleotide triphosphates

Question 29

What nucleotide is methylated to produce dTMP?

A) dAMP
B) dCMP
C) dGMP
D) dUMP
E) both dCMP and dUMP can be converted to dTMP

Question 30

Which is NOT a strategy of ribonucleotide reductase to afford a proper balance of dNTPs for the cell? In general:

A) adenosine nucleotides in the regulatory site $\rightarrow$ pyrimidine nucleotides recognized in the catalytic site
B) dGTP in the regulatory site $\rightarrow$ ADP recognized in the catalytic site
C) dATP in the regulatory site $\rightarrow$ GDP recognized in the catalytic site
D) dTTP in the regulatory site $\rightarrow$ GDP in the catalytic site
E) adenosine nucleotides in the regulatory site $\rightarrow$ varied subunit stoichiometries

Question 31

In general, as nucleotides are catabolized,

A) dephosphorylation is followed by deglycosylation then bases undergo deamination/oxidation
B) deglycosylation is followed by dephosphorylation then bases undergo deamination/oxidation
C) bases undergo deamination/oxidation followed by deglycosylation, then dephosphorylation
D) bases undergo deamination/oxidation, followed by dephosphorylation then deglycosylation
E) dephosphorylation is followed by bases undergoing deamination/oxidation, then deglycosylation

Question 32

Defects in adenosine deaminase lead to increased ___ levels, which impact ribonucleotide reductase and further lead to ___ and SCID.

A) dGTP, imbalance of dNTPs
B) dATP, imbalance of dNTPs
C) ATP, deficient metabolic energy
D) GTP, deficient cell signaling ability
E) ATP, imbalance of NTPs

Question 33

SCID devastating effects are due to ___ in immune cells, which must be ___ to be effective

A) decreased DNA synthesis, rapidly growing
B) decreased ATP synthesis, metabolically active
C) decreased antibody synthesis, rapidly growing
D) increased uric acid deposits, able to circulate freely in blood
E) inhibition of uric acid production, apoptotic

Question 34

Which is NOT true of uric acid?

A) It is elevated in Lesch-Nyhan syndrome
B) It is eliminated by the kidneys
C) Crystals of uric acid may accumulate causing kidney stones
D) It is water insoluble
E) Some animals excrete uric acid in solid waste

Question 35

Recombinant forms of the enzyme urate oxidase are available for therapeutic purposes. Based on the information in this chapter, the condition in which this therapy might be useful is _____

Question 36

During the turnover of nucleic acids some purines can be reincorporated into nucleotides via _____ pathways.

Question 37

Gout is treated using the compound ______.

Question 38

Which of the following organisms excrete uric acid?

A) birds
B) reptiles
C) primates
D) A and B are correct
E) all of the above are correct

Question 39

The disease gout is characterized by high levels of _____, which forms crystal deposits of _____, resulting in painful joints

A) urea; uric acid
B) uric acid; monosodium urate
C) sodium urate; urea
D) uric acid; urea
E) none of the above

Question 40

Which of the following is formed as a result of pyrimidine metabolism?

A) alanine
B) aspartate
C) asparagine
D) glycine
E) $\beta$ -alanine