16) Precursors for the biosynthesis of the pyrimidine ring system include: a) ca
ID: 831063 • Letter: 1
Question
16) Precursors for the biosynthesis of the pyrimidine ring system include:
a) carbamoyl phosphate and aspartate.
b) glutamate, NH3, and CO2.
c) glycine and succinyl-CoA.
d) glycine, glutamine, CO2, and aspartate.
e) inosine and aspartate.
17) Which of the following is not true of the reaction catalyzed by ribonucleotide
reductase?
a) Glutathione is part of the path of electron transfer.
b) It acts on nucleoside diphosphates.
c) Its mechanism involves formation of a free radical.
d) There is a separate enzyme for each nucleotide (ADP, CDP, GDP, UDP).
e) Thioredoxin acts as an essential electron carrier.
18) The anticancer drug FUdR (fluorodeoxyuridine) is metabolized by cells to the
nucleotide FdUMP, a dTMP analog and suicide substrate inhibitor of
thymidylate synthase. The nucleotide salvage metabolic enzyme that catalyzes
the conversion of FUdR to FdUMP is:
a) Thymidine phosphorylase
b) Thymidylate kinase
c) Thymidine kinase
d) (d)NMP kinase
e) thymidine phosphoribosyl transferase
Chem 4413 Homework 1 Spring 2014
19) A cell that is unable to synthesize or obtain tetrahydrofolic acid (H4 folate)
would probably be deficient in the biosynthesis of:
a) CMP.
b) GMP.
c) orotate.
d) thymidylate (TMP).
e) UMP.
20) An intermediate of purine degradation in humans is:
a) glutamate.
b) NH4
c) succinate.
d) urea.
e) uric acid.
Explanation / Answer
16)d) glycine, glutamine, CO2, and aspartate.
17)b) It acts on nucleoside diphosphates
18)c) Thymidine kinase.
19)d) thymidylate (TMP).
20)d) urea.
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