Deck 25: Nucleotide Biosynthesis

Question 1

What is the intermediate in the conversion of inosinate to guanylate?

A) adenylate
B) cytidylate
C) guanylate
D) orotidylate
E) xanthylate

Answer 1

E

Question 2

A purine or pyrimidine base linked to a sugar is a _____.

A) nucleotide
B) nucleoside
C) ribonucleotide
D) deoxynucleotide
E) None of the answers is correct.

Answer 2

B

Question 3

_______________ disease is caused by a genetic mutation resulting in the absence of hypoxanthine-guanine phosphoribosyl transferase.

Answer 3

Lesch-Nyhan

Question 4

Amination of _____ produces CTP.

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

Question 5

Which of the following is the final degradation product of purine catabolism?

A) xanthine
B) hypoxanthine
C) inosine
D) urate
E) None of the answers is correct.

Question 6

Which of the following is the methyl donor in the synthesis of dTMP from dUMP?

A) N⁵-methyltetrahydrofolate
B) N⁵, N¹⁰-methylenetetrahydrofolate
C) S-adenosylmethionine
D) methylcobalamin
E) None of the answers is correct.

Question 7

The enzyme that catalyzes the generalized equation XDP + YTP $\rightarrow$ XTP + YDP is _________.

Question 8

Scaffolds on which the ring systems in nucleotides are assembled are the amino acids glycine and _______________.

Question 9

Hypoxanthine-guanine phosphoribosyltransferase catalyzes the formation of guanylate and _______________.

Question 10

The two nucleotides that can serve as energy currency in certain biomolecular paths are ATP and _______________.

Question 11

Assembly of a nucleoside from PRPP and a pre-existing base is known as a(n) _____ pathway.

A) salvage
B) synthetic
C) catabolic
D) anabolic
E) de novo

Question 12

Some individuals with a deficiency in the enzyme adenosine deaminase exhibit _______________ (bubble boy disease).

Question 13

The committed step in purine nucleotide biosynthesis is the conversion of _______________ to phosphoribosylamine.

Question 14

Which nucleotide is most commonly used as an energy currency?

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

Question 15

Which of the following is decarboxylated to form uridylate?

A) adenylate
B) cytidylate
C) guanylate
D) orotidylate
E) None of the answers is correct.

Question 16

What disease is caused by high levels of urate?

A) severe combined immunodeficiency
B) Lesch-Nyhan syndrome
C) gout
D) spina bifida
E) None of the answers is correct.

Question 17

Dihydrofolate reductase is an excellent target for anticancer drugs because it is critical in the synthesis of _______________.

Question 18

The conversion of ribonucleotides to deoxyribonucleotides is catalyzed by ________________.

Question 19

In ______________ biosynthesis, the base is assembled first and then attached to ribose.

Question 20

Assembly of a compound from simpler molecules not salvaged from pre-existing similar molecules is known as a(n) _____ pathway.

A) salvage
B) synthetic
C) catabolic
D) anabolic
E) de novo

Question 21

What is/are the advantage or advantages of channeling intermediates by carbamoyl phosphate synthetase?

Question 22

Allopurinol is used to treat gout and is an inhibitor of the enzyme

A) xanthine oxidase.
B) xanthine hydrolase.
C) hypoxanthine-guanine phosphoribosyl transferase.
D) urate oxidase
E) None of the answers is correct.

Question 23

In de novo synthesis, the pyrimidine ring is assembled using

A) bicarbonate.
B) asparagine
C) NH₃ from glutamine.
D) glycine
E) bicarbonate and NH₃ from glutamine.

Question 24

All of the nitrogen atoms found in nucleotides are ultimately derived from

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

Question 25

The ultimate reductant in synthesis of deoxyribonucleotides is

A) FADH₂.
B) NADH.
C) NADPH.
D) quinine.
E) None of the answers is correct.

Question 26

Given the function of nucleotides, would you expect their synthesis to be simple or complex and diverse?

Question 27

Which of the following is a competitive inhibitor of dihydrofolate reductase that is effective for anticancer chemotherapy?

A) aminopterin
B) methotrexate
C) fluorouracil
D) trimethoprim
E) aminopterin and methotrexate

Question 28

How many ATP molecules are necessary to make carbamoyl phosphate by carbamoyl phosphate synthetase (CPS)?

A) 1
B) 2
C) 3
D) 4
E) It depends whether the reaction takes place in the cytosol or mitochondria.

Question 29

The displacing nucleophile in pyrimidine synthesis is typically

A) ammonia or an amino group.
B) a metal ion.
C) coenzyme A.
D) pyridoxamine.
E) None of the answers is correct.

Question 30

Tetrahydrofolate is generated from dihydrofolate by dihydrofolate reductase and uses the reductant

A) FADH₂.
B) NADH.
C) NADPH.
D) riboflavin.
E) None of the answers is correct.

Question 31

Which enzyme(s), in nucleotide biosynthesis pathways, use(s) a substrate channeling mechanism?

A) carbamoyl phosphate synthetase
B) nucleoside monophosphate kinase
C) glutamine phosphoribosyl amidotransferase
D) aspartate transcarbamoylase
E) carbamoyl phosphate synthetase and glutamine phosphoribosyl amidotransferase

Question 32

In the de novo synthesis of DNA and RNA,

A) ribonucleotides are made from deoxynucleotides.
B) deoxyribonucleotides are made from ribonucleotides.
C) dideoxyribonucleotides are the precursors for both.
D) ribonucleotides and deoxyribonucleotides are made by independent pathways.
E) None of the answers is correct.

Question 33

What is an ATP-grasp fold?

Question 34

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

Question 35

In addition to UTP, the synthesis of CTP from UTP requires __________

A) glutamine and ATP.
B) glycine and ATP.
C) glutamine, ATP, and NADH.
D) glycine and TTP.
E) None of the answers is correct.

Question 36

Why is nucleotide synthesis an important pathway for medical intervention? What types of disease could be treated using this information?

Question 37

TMP is made from

A) dTMP.
B) UTP.
C) CTP.
D) ATP.
E) None of the answers is correct.

Question 38

Briefly describe, in one or two sentences, the reaction by which carbamoyl phosphate synthetase acquires an ammonia to make carbamoyl phosphate.

Question 39

What enzyme carries out this reaction? UMP + ATP $\leftrightarrow$ UDP + ADP

A) nucleoside triphosphate kinase
B) nucleoside diphosphate kinase
C) ATP kinase
D) UMP kinase
E) None of the answers is correct.

Question 40

Inosinate can be converted to

A) AMP.
B) GMP.
C) UMP.
D) CMP.
E) AMP or GMP.

Question 41

What vitamin supplement is taken during the first trimester of pregnancy to prevent the birth defect known as spina bifida?

Question 42

How is ATCase, a key enzyme in pyrimidine biosynthesis, inhibited?

Question 43

What is significant about the fact that E. coli ribonucleotide reductase contains two allosteric sites?

Question 44

What reaction actually forms the six-member ring found in pyrimidines?

Question 45

Why do purine-salvage pathways save the cell energy?

Question 46

How is the reciprocal use of nucleotides useful in purine synthesis?

Question 47

What is the disadvantage of methotrexate as a therapeutic agent?

Question 48

What are advantages of high urate levels such as those found in higher primates (like humans)?

Question 49

What is a general theme in purine ring synthesis, in terms of reaction logic and mechanism?

Question 50

What is the approximate rate change when the enzyme orotidylate decarboxylase decarboxylates orotidylate to form UMP?