Chapter 32 Nucleotide Metabolism
Matching Questions
Use the following to answer questions 1–10:
Choose the correct answer from the list below. Not all of the answers will be used.
a) de novo
b) xanthylate
c) riboflavin
d) amino acids
e) UTP
f) N5, N10-methylenetetrahydrofolate
g) nucleotide
h) gout
i) nucleoside
j) ATP
k) urate
l) salvage
1.
Purines and pyrimidines are derived from _________________.
2.
Assembly of a compound from simpler molecules is known as a(n) _______________ pathway.
Ans:
Section: 32.1
3.
Assembly of a compound from phophoribosylpyrophosphate (PRPP) and a base is known as
a(n) _________________ pathway.
Ans:
Section: 32.1
4.
A purine or pyrimidine base linked to a sugar is a(n) _________________.
Ans:
Section: 32.1
5.
A purine or pyrimidine base linked to a sugar and to a phosphate ester is a(n)
_________________.
Section: 32.1
6.
CTP is formed by the amination of _________________.
Ans:
Section: 32.2
7.
The intermediate between inosinate and guanylate is _________________.
Ans:
b
Section: 32.3
Ans:
d
Section: Introduction
Chapter 32 Nucleotide Metabolism
2
8.
The methyl donor to make TMP is _________________.
9.
High levels of urate cause the disease _________________.
Ans:
h
Section: 32.6
10.
The final product of purine degradation is _________________.
Ans:
k
Section: 32.6
Fill–in-the-Blank Questions
11.
DNA is built from _____.
Ans: deoxyribonucleotides Section: 32.1
12.
Scaffolds for the ring systems in nucleotides are from the amino acids glycine and _____.
Ans: aspartate Sections: 32.2, 32.3
13.
In _____ biosynthesis the base is assembled first and then attached to ribose.
Ans: pyrimidine Section: 32.2
14.
Hypoxanthine-guanine phosphoribosyltransferase catalyzes the formation of guanylate and
_____.
Ans: inosinate Section: 32.3
15.
Fluorouracil acts as an analog of _____.
Ans: dUMP Section: 32.4
16.
Dihydrofolate reductase is an excellent target for anticancer drugs because it is critical in the
synthesis of _____.
Ans: thymidylate Section: 32.4
17.
The conversion of ribonucleotides to deoxyribonucleotides is catalyzed by _____.
Ans: ribonucleotide reductase Section: 32.4
18.
The committed step in purine nucleotide biosynthesis is the conversion of _____ to 5-
phosphoribosyl-1-amine.
Ans: PRPP Section: 32.3
19.
_____ disease is caused by a genetic mutation resulting in the absence of hypoxanthine-guanine
phosphoribosyltransferase.
Ans: Lesch-Nyhan Section: 32.6
20.
Some individuals with a deficiency in the enzyme adenosine deaminase exhibit _____.
Ans: severe combined immunodeficiency (SCID) Section: 32.6
Ans:
Section: 32.4
Chapter 32 Nucleotide Metabolism
3
Multiple-Choice Questions
21.
The source(s) of NH2 groups in the synthesis of nucleotides is(are)
A)
aspartate.
B)
glutamine.
C)
glycine.
D)
A and B.
E)
A, B, and C.
22.
Both de novo and salvage paths are used in the synthesis of
A)
ribonucleotides.
B)
deoxyribonucleotides.
C)
dideoxyribonucleotides.
D)
All of the above.
E)
None of the above.
Ans: A Section: 32.2, 32.3
23.
TMP is made from
A)
dTMP.
B)
dUMP.
C)
CTP.
D)
ATP.
E)
None of the above.
Ans: B Section: Figure 32.4
24.
In de novo synthesis, the pyrimidine ring is assembled using
A)
bicarbonate.
B)
aspartate.
C)
glutamine.
D)
A and B.
E)
A, B, and C.
Ans: E Section: 32.3
25.
How many ATP molecules are necessary to make carbamoyl phosphate by carbamoyl phosphate
synthetase (CPS)?
A)
1
B)
4
C)
2
D)
3
E)
None of the above.
Ans: C Section: 32.1
26.
Which enzyme carries out this reaction: XDP + YTP ↔ XTP + YDP?
A)
nucleoside triphosphate kinase
B)
nucleoside diphosphate kinase
C)
nucleoside diphosphate phosphorylase
D)
nucleoside triphosphate phosphorylase
E)
None of the above.
Ans: B Section: 32.2
Ans: D Section: 32.2
Chapter 32 Nucleotide Metabolism
4
27.
The synthesis of CTP from UTP requires UTP and
A)
glutamine and ATP.
B)
glycine and ATP.
C)
glutamine, ATP, and NADH.
D)
All of the above.
E)
None of the above.
28.
Which enzyme(s) catalyze(s) the first step in de novo nucleotide biosynthesis?
A)
aspartate transcarbamylase
B)
nucleoside monophosphate kinase
C)
glutamine phosphoribosyl amidotransferase
D)
A and B.
E)
A and C.
Ans: C Section: 32.3
29.
The displacing nucleophile in pyrimidine synthesis is typically
A)
ammonia or an amino group.
B)
a metal ion.
C)
coenzyme A.
D)
All of the above.
E)
None of the above.
Ans: A Section: 32.2
30.
Inosinate can be converted to
A)
AMP.
B)
GMP.
C)
UMP.
D)
A or B.
E)
A, B, or C.
Ans: D Section: 32.3
31.
The ultimate reductant in synthesis of deoxyribonucleotides is
A)
FADH2.
B)
NADH.
C)
NADPH.
D)
quinone.
E)
None of the above.
Ans: C Section: 32.4
32.
Which amino acid side chain in thymidylate synthase activates the ring of dUMP, making C-5 a
good nucleophile?
A)
cysteine
B)
aspartate
C)
glutamine
D)
tyrosine
E)
serine
Ans: A Section: 32.4
Ans: A Section: 32.2
Chapter 32 Nucleotide Metabolism
5
33.
Tetrahydrofolate is generated from dihydrofolate by dihydrofolate reductase and uses the
reductant
A)
FADH2.
B)
NADH.
C)
NADPH.
D)
riboflavin.
E)
None of the above.
34.
The competitive inhibitor(s) of dihydrofolate reductase is(are)
A)
aminopterin.
B)
methotrexate.
C)
fluorouracil.
D)
A and B.
E)
B and C.
Ans: D Section: 32.4
35.
Allopurinol is used to treat gout and is an inhibitor of the enzyme(s)
A)
xanthine oxidase.
B)
xanthine hydrolase.
C)
hypoxanthine-guanine phosphoribosyltransferase.
D)
All of the above.
E)
None of the above.
Ans: A Section: 32.6
36.
Sulfa drugs are analogs of p-aminobenzoate, a compound necessary for N10–
formyltetrahydrofolate. How do these drugs act on bacterial infections and why are humans not
susceptible?
A)
N10-formyltetrahydrofolate is a ferredoxin analog and a potent inhibitor of ribonucleotide
reductase in bacteria but not humans.
B)
N10-formyltetrahydrofolate is a ferredoxin analog and a potent inhibitor of ribonucleotide
reductase, but humans consume sufficient quantities of ferredoxin in their diet to saturate
the reductase.
C)
N10-formyltetrahydrofolate is an NADPH analog and a potent inhibitor of ribonucleotide
reductase in bacteria but not humans.
D)
N10-formyltetrahydrofolate twice transfers a formyl group during de novo synthesis of the
purine ring. Bacteria dihydrofolate reductase is blocked by sulfa drugs, whereas the
human enzyme is not.
E)
N10-formyltetrahydrofolate twice transfers a formyl group during de novo synthesis of the
purine ring. Bacteria synthesize their own folate, whereas humans get theirs from eating
green plants.
Ans: E Section: 32.3
Ans: C Section: 32.4
Chapter 32 Nucleotide Metabolism
6
37.
What intermediate in pyrimidine synthesis will accumulate if a strain of bacteria is lacking in
aspartate?
A)
orotidylate
B)
orotate
C)
dihydroorotate
D)
5-phosphoribosyl-1-amine
E)
carbamoyl phosphate
38.
Pyrimidine biosynthesis is allowed to take place in the presence of [15N]aspartate. What position
would be labeled in the newly synthesized nucleotides?
A)
N3 in IMP
B)
N7 in IMP
C)
N9 in Imp
D)
N1 in UTP
E)
N3 in UTP
Ans: D Section: 32.1
39.
Human beings contain two different carbamoyl phosphate synthetase enzymes. If you wanted to
study the enzyme inhibition for the enzyme specific for nucleotide synthesis, which of the
following analogs would you choose?
A)
analog for bicarbonate
B)
analog for carboxyphosphate
C)
analog for carbamic acid
D)
analog for NH3
E)
analog for glutamine
Ans: E Section: 32.2
40.
How is the purine nucleotide cycle linked to the citric acid cycle?
A)
The purine nucleotide cycle serves as an anapleurotic reaction for the formation of
oxaloacetate.
B)
The purine nucleotide cycle serves as an anapleurotic reaction for the formation of
fumarate.
C)
The purine nucleotide cycle serves as an anapleurotic reaction for the formation of
pyruvate.
D)
The condensation of IMP with glutamate generates adenylosuccinate, which is
hydrolyzed to form succinate.
E)
The condensation of IMP with glutamine generates adenylosuccinate, which is
hydrolyzed to form succinate.
Ans: B Section: 32.3
Short-Answer Questions
Ans: E Section: 32.2
Chapter 32 Nucleotide Metabolism
7
41.
Why is nucleotide synthesis an important pathway for medical intervention? What types of
disease could be treated using this information?
42.
Given the function of nucleotides, would you expect their synthesis to be simple or complex and
diverse?
reactions were utilized and small metabolic pathway differences developed that
accompanied the need to make different nucleotides.
Section: 32.1
43.
Describe the reaction by which carbamoyl phosphate synthetase acquires an ammonia to make
carbamoyl phosphate.
Ans:
A component of the enzyme hydrolyzes glutamine, forming glutamate and ammonia.
Section: 32.2
44.
What is the advantage of channeling intermediates by carbamoyl phosphate synthetase?
then channeled to the site of carbamoyl phosphate synthesis. The substrates are protected
from hydrolysis, and not lost by diffusion.
Section: 32.2
45.
What reaction actually forms the six-member ring found in pyrimidines?
nitrogen poised near a carboxylic acid group. These groups react and cyclization results
in dihydroorotate formation.
Section: 32.2
46.
How is pyrimidine biosynthesis regulated?
transcarbamoylase (ATCase). ATCase is activated by ATP and is inhibited by the final
product of de novo pyrimidine synthesis, CTP.
Section: 32.5
47.
Why do purine salvage pathways save the cell energy?
Ans:
Free purines can be attached to PRPP in a single-step reaction to form nucleoside
monophosphates.
Section: 32.3
48.
What is a general theme in purine ring synthesis, in terms of reaction logic and mechanism?
carbon-bound oxygen atom, followed by loss of the phosphoryl group, via a displacement
reaction in which a nucleophile acts as the displacing agent.
Section: 32.3
in cancer therapy.
Sections: 32.5 and 32.6
Chapter 32 Nucleotide Metabolism
8
49.
How is the reciprocal use of nucleotides useful in purine synthesis?
50.
What is the disadvantage of methotrexate as a therapeutic agent?
loss of immune system protection, nausea, and hair loss.
Section: 32.6
51.
How is ATCase, a key enzyme in pyrimidine biosynthesis, inhibited?
classic example of feedback inhibition.
Section: 32.5
52.
Which vitamin supplement is taken during the first trimester of pregnancy to prevent the birth
defect known as spina bifida?
precursors required during frequent cell division and substantial DNA synthesis.
Section: 32.6
53.
What are advantages of high urate levels?
Ans:
Urate is a highly effective scavenger of reactive oxygen species (ROS).
Section: 32.6
an opportunity for balance in the regulatory processes.
Section: 32.3