Deck 22: Nucleotide Metabolism

Question 1

Which enzyme of the pyrimidine synthesis pathway is the most highly regulated?

A)carbamoyl phosphate synthetase
B)aspartate transcarbamoylase
C)orotate phosphoribosyltransferase
D)UMP kinase
E)nucleoside diphosphate kinase

Answer 1

B

Question 2

What molecule contributes at least two nitrogen atoms to each purine?

A)asparagine
B)10-formyltetrahydrofolate
C)glycine
D)glutamine
E)carbamoyl phosphate

Answer 2

D

Question 3

Which enzyme of the inosinic acid biosynthesis pathway is the major control point for purine synthesis?

A)phosphoribosyl pyrophosphate amidotransferase
B)glycinamide ribonucleotide transformylase
C)formylglycinamidine ribonucleotide amidotransferase
D)5-aminoimidazole ribonucleotide synthetase
E)5-aminoimidazole ribonucleotide carboxylase

Answer 3

A

Question 4

While endonucleases cleave nucleic acids into smaller oligonucleotides, __________ are responsible for cleaving the oligonucleotides into nucleotides.

A)phosphodiesterases
B)nucleotidase
C)nucleoside kinases
D)phosphorylases
E)phosphoribosyl transferases

Question 5

Which of the following is a product of xanthine dehydrogenase?

A)hypoxanthine
B)uric acid
C)guanine
D)xanthosine
E)allantoin

Question 6

During the conversion of IMP to GMP and AMP, __________ serves as the nitrogen source for GMP, while _________ serves as the nitrogen source for AMP.

A)glutamate, asparagine
B)glutamate, aspartate
C)glutamine, asparagine
D)glutamine, aspartate
E)none of the above

Question 7

The ten enzyme activities that convert PRPP to inosinic acid are part of a multienzyme complex known as the _________.

A)IMP synthetase complex
B)purine synthetase complex
C)purinosome
D)tetrahydrofolate synthase complex
E)none of the above

Question 8

Which of the following correctly describes the activity or regulation of E coli ribonucleotide reductase?

A)the overall activity of the enzyme is controlled by ATP and dATP
B)the specificity of the enzyme is controlled by all four dNTPs
C)a tyrosine free radical participates in the reaction
D)the reduction is not a result of simple hydride transfer
E)all of the above

Question 9

Which of the following coenzymes contains an adenylate group?

A)cobalamin
B)tetrahydrofolate
C)thiamine pyrophosphate
D)pyridoxal phosphate
E)coenzyme A

Question 10

Which of the following is the correct structure for PRPP?

A)
B)
C)
D)
E)none of the above

Question 11

What molecule(s)is(are)the source of the two nitrogen atoms for pyrimidine synthesis?

A)asparagine
B)glutamine, glutamate
C)aspartate, carbamoyl phosphate
D)carbamoyl phosphate, glutamine
E)aspartate, glutamate

Question 12

Which of the following best explains the initial steps for the synthesis of deoxynucleotides?

A)begins with reduction of the ribose residue in PRPP
B)deoxy PRPP is formed from deoxyribose-5-phosphate
C)formed by reduction of ribonucleotide counterparts
D)formed by oxidation of ribonucleotide counterparts
E)none of the above

Question 13

The end products of the pyrimidine catabolic pathway are ammonia, carbon dioxide and __________.

A)asparagine
B)aspartic acid
C)dihydrouracil
D) $\beta$ -alanine
E)glutamate

Question 14

When ATP is bound in the activity site and ______ is bound in the specificity site, _______ will be reduced by ribonucleotide reductase.

A)ATP; ADP and GDP
B)dATP; GDP, UDP and CDP
C)dTTP; GDP and ADP
D)dGTP; ADP
E)none of the above are correct

Question 15

Which of the following shows the correct and complete flow of electrons for ribonucleotide reductase?

A)NADH $\rarr$ FAD $\rarr$ thioredoxin $\rarr$ ribonucleotide reductase
B)NADPH $\rarr$ glutathione $\rarr$ glutaredoxin $\rarr$ ribonucleotide reductase
C)NADPH $\rarr$ thioredoxin $\rarr$ cytochrome-b $\rarr$ ribonucleotide reductase
D)FADH₂ $\rarr$ glutathione $\rarr$ glutaredoxin $\rarr$ ribonucleotide reductase
E)none of the above

Question 16

The following reaction is catalyzed by what enzyme?

A)xanthine oxidoreductase
B)hypoxanthine hydroxylase
C)urate oxidase
D)guanine oxidase
E)none of the above

Question 17

Which of the following correctly explains the relationship between xanthine dehydrogenase (XDH)and xanthine oxidase (XO)?

A)in healthy tissue, XDH is abundant while XO is rarely found
B)conversion of XDH to XO occurs under conditions that damage cells
C)XDH is converted to XO by formation of a disulfide bond
D)XDH is converted to XO by proteolysis
E)all of the above

Question 18

Which of the following describes the coenzyme involved with thymidylate synthase?

A)5-methyl-THF serves as the methyl donor
B)10-methyl-THF serves as the methyl donor
C)5,10-methylene-THF serves as both methylene donor and reducing agent
D)5,10-methenyl-THF serves as both methylene donor and reducing agent
E)S-adenosylmethionine serves as the methyl donor

Question 19

Which of the following best explains the enzyme(s)involved in ribonucleotide reduction?

A)there is 1 enzyme for each of the 4 different nucleotides
B)1 enzyme for pyrimidine nucleotides and 1 for purine nucleotides
C)1 enzyme for pyrimidine nucleotides, 1 for ADP and 1 for GDP
D)1 enzyme for purine nucleotides, 1 for CDP and 1 for UDP
E)1 enzyme for all 4 nucleotides

Question 20

Which of the following sequence of events best explains the formation of carbamate in the mechanism of carbamoyl phosphate synthetase?

A)Bicarbonate and ATP form carboxyphosphate, then NH₃ performs a nucleophilic attack on carboxyphosphate to form carbamate
B)Bicarbonate is attacked by NH₃ to produce carbamate with ATP hydrolysis occurring solely to drive the reaction to completion
C)Bicarbonate reacts with ATP forming carboxy adenylate and pyrophosphate, then NH₃ performs a nucleophilic attack on carboxy adenylate to form carbamate
D)NH₃ reacts with ATP, which then reacts with bicarbonate followed by loss of phosphate to produce carbamate
E)none of the above

Question 21

Show the reaction of allopurinol with xanthine dehydrogenase and explain how this molecule functions as an inhibitor of the enzyme.

Question 22

Below is the structure of 3'-azido-2',3'-dideoxythymidine (also known as AZT). Draw the structure of the metabolite of AZT that serves as the inhibitor of reverse transcriptase.

Question 23

Given the structure of GMP, indicate the source for all carbons and nitrogens in the guanine base.

Question 24

The following molecule is an irreversible inhibitor of which enzyme of nucleotide metabolism?

A)ribonucleotide reductase
B)thymidylate synthase
C)thymidine kinase
D)dCMP deaminase
E)CTP synthetase

Question 25

The molecule below would be an analog of __________ and therefore an effective _________compound.

A)adenosine; anticancer
B)adenosine; antiviral
C)guanosine; anticancer
D)guanosine; antiviral
E)none of the above