Question 1

Tyr122 is important in the mechanism of the E.coli ribonucleotide reductase.The function of this amino acid in the mechanism is to

Accepted Answer

A)  carry out a nucleophilic attack on the substrate. 
B)  coordinate water in the active site. 
C)  generate the Cys439 radical species. 
D)  hydrogen-bond to the phosphates of the substrate. 
A)  carry out a nucleophilic attack on the substrate. 
B)  coordinate water in the active site. 
C)  generate the Cys439 radical species. 
D)  hydrogen-bond to the phosphates of the substrate. C

Question 2

During the biosynthesis of UMP from carbamoyl phosphate and aspartate,dihydroorotate is converted to which of the following compounds?

Accepted Answer

A)  carbamoyl aspartate 
B)  orotate 
C)  orotidine-   -monophosphate 
D)  quinone 
A)  carbamoyl aspartate 
B)  orotate 
C)  orotidine-   -monophosphate 
D)  quinone B

Question 3

Contrast the source of the nitrogen required for the conversion of UTP to CTP in humans and bacteria.

Accepted Answer

Humans use glutamine,whereas bacteria use ammonia (NH₄₊).

Question 4

The activity site of ribonucleotide reductase can bind two different molecules,whereas the specificity site can bind several.Construct a situation where the activity of the enzyme is inhibited by choosing the identity of the molecules bound to each site.

Accepted Answer

The enzyme would be inhibited

Question 5

Two biosynthesis steps are necessary to incorporate the carbon from HCO3     
into carbamoyl aspartate.Describe the intermediate compound generated during this conversion.

Accepted Answer

Carbamoyl phosphate,which is f

Question 6

Consider the breakdown of the four compounds below.Which would be expected to generate   -alanine?

Accepted Answer

A)  dATP 
B)  dGMP 
C)  dCMP 
D)  dTMP 
A)  dATP 
B)  dGMP 
C)  dCMP 
D)  dTMP

Question 7

To determine the role of glutaredoxin in the generation of deoxyribonucleotides by ribonucleotide reductase,which organisms would be the best to study?

Accepted Answer

A)  bony fish 
B)  bacteria 
C)  humans 
D)  amphibians 
A)  bony fish 
B)  bacteria 
C)  humans 
D)  amphibians

Question 8

Several cysteines play important roles in the mechanism of E.coli ribonucleotide reductase.Which is NOT a role carried out by cysteine in this enzyme?

Accepted Answer

A)  donation of a hydrogen atom to the substrate 
B)  removal of a hydrogen atom from the substrate 
C)  donation of a proton to ultimately form water 
D)  reduction of thioredoxin 
A)  donation of a hydrogen atom to the substrate 
B)  removal of a hydrogen atom from the substrate 
C)  donation of a proton to ultimately form water 
D)  reduction of thioredoxin

Question 9

Analysis of enzyme activities in a cell in the absence and presence of AMP and GMP is completed.Which enzyme would show lower activity when AMP is added but not when GMP is added?

Accepted Answer

A)  glutamine-PRPP aminotransferase 
B)  adenylosuccinate synthase 
C)  IMP dehydrogenase 
D)  PRPP synthetase 
A)  glutamine-PRPP aminotransferase 
B)  adenylosuccinate synthase 
C)  IMP dehydrogenase 
D)  PRPP synthetase

Question 10

Glutamine-PRPP amidotransferase is a tetrameric enzyme that displays sigmoidal kinetics when no inhibitors are present.In the presence of either GTP or ATP the kinetics curve is sigmoidal.Why does this difference in kinetics occur?

Accepted Answer

Both GTP a

Question 11

Analysis of AMP and GMP synthesized in E.coli grown in medium containing 15N-labeled aspartate would show that

Accepted Answer

A)  AMP contained twice as much 15N than GMP. 
B)  GMP contained twice as much 15N than AMP. 
C)  AMP contained three times as much 15N than GMP. 
D)  they contain the same levels of 15N. 
A)  AMP contained twice as much 15N than GMP. 
B)  GMP contained twice as much 15N than AMP. 
C)  AMP contained three times as much 15N than GMP. 
D)  they contain the same levels of 15N.

Question 12

The transformation of ribose-5-phosphate to AIR in the first stage of purine biosynthesis in E.coli consumes the equivalent of 5 ATP.The second stage consumes

Accepted Answer

A)  an additional 5 ATP. 
B)  more than 5 ATP. 
C)  less than 5 ATP and generates 1 ATP. 
D)  less than 5 ATP. 
A)  an additional 5 ATP. 
B)  more than 5 ATP. 
C)  less than 5 ATP and generates 1 ATP. 
D)  less than 5 ATP.

Question 13

The nitrogen atoms of a purine originate from all of the following amino acids EXCEPT

Accepted Answer

A)  glycine. 
B)  aspartate. 
C)  cysteine. 
D)  glutamine. 
A)  glycine. 
B)  aspartate. 
C)  cysteine. 
D)  glutamine.

Question 14

The carbon atoms of a purine originate from glycine and

Accepted Answer

A)  N10-formyl-THF. 
B)  aspartate. 
C)  glycinamide. 
D)  glutamate. 
A)  N10-formyl-THF. 
B)  aspartate. 
C)  glycinamide. 
D)  glutamate.

Question 15

Consider a cell that is provided aspartate in which all carbons are radioactively labeled.Compounds in the cell are analyzed after the biosynthesis and subsequent breakdown of pyrimidines.Which of the following compounds would display no radioactivity signal during the analysis?

Accepted Answer

A)    -alanine 
B)  glutamine 
C)    -aminoisobutyrate 
D)  dihydrouracil 
A)    -alanine 
B)  glutamine 
C)    -aminoisobutyrate 
D)  dihydrouracil

Question 16

Explain how the feedback inhibition of IMP dehydrogenase by GMP can increase the flux of the ATP synthesis pathway.

Accepted Answer

IMP is a common precursor for

Question 17

When analyzing the production of dTMP by thymidylate synthase in a cell-free system,which of the following compounds would be found as an additional product of this enzyme?

Accepted Answer

A)  7,8-dihydrofolate 
B)  NADP+ 
C)  N5,N10-methylenetetrahydrofolate 
D)  glycine 
A)  7,8-dihydrofolate 
B)  NADP+ 
C)  N5,N10-methylenetetrahydrofolate 
D)  glycine

Question 18

What would be the effect on thymidylate synthase activity if raltitrexed is present?

Accepted Answer

Thymidylat

Question 19

Which answer INCORRECTLY pairs a substrate and subsequent product of dihydropyrimidine dehydrogenase?

Accepted Answer

A)  thymine; dihydrothymine 
B)  uracil; dihydrouracil 
C)  adenine; dihydroadenine 
D)  5-fluorouracil; fluorodihydrouracil 
A)  thymine; dihydrothymine 
B)  uracil; dihydrouracil 
C)  adenine; dihydroadenine 
D)  5-fluorouracil; fluorodihydrouracil

Question 20

Which of the following is a coenzyme that is derived from ATP?

Accepted Answer

A)  coenzyme Q 
B)  FAD 
C)  heme 
D)  Fe4-S4 cluster 
A)  coenzyme Q 
B)  FAD 
C)  heme 
D)  Fe4-S4 cluster

Exam 18: Nucleotide Metabolism

Tyr122 is important in the mechanism of the E.coli ribonucleotide reductase.The function of this amino acid in the mechanism is to

During the biosynthesis of UMP from carbamoyl phosphate and aspartate,dihydroorotate is converted to which of the following compounds?

Contrast the source of the nitrogen required for the conversion of UTP to CTP in humans and bacteria.

The activity site of ribonucleotide reductase can bind two different molecules,whereas the specificity site can bind several.Construct a situation where the activity of the enzyme is inhibited by choosing the identity of the molecules bound to each site.

Two biosynthesis steps are necessary to incorporate the carbon from HCO3 into carbamoyl aspartate.Describe the intermediate compound generated during this conversion.

Consider the breakdown of the four compounds below.Which would be expected to generate -alanine?

To determine the role of glutaredoxin in the generation of deoxyribonucleotides by ribonucleotide reductase,which organisms would be the best to study?

Several cysteines play important roles in the mechanism of E.coli ribonucleotide reductase.Which is NOT a role carried out by cysteine in this enzyme?

Analysis of enzyme activities in a cell in the absence and presence of AMP and GMP is completed.Which enzyme would show lower activity when AMP is added but not when GMP is added?

Glutamine-PRPP amidotransferase is a tetrameric enzyme that displays sigmoidal kinetics when no inhibitors are present.In the presence of either GTP or ATP the kinetics curve is sigmoidal.Why does this difference in kinetics occur?

Analysis of AMP and GMP synthesized in E.coli grown in medium containing 15N-labeled aspartate would show that

The transformation of ribose-5-phosphate to AIR in the first stage of purine biosynthesis in E.coli consumes the equivalent of 5 ATP.The second stage consumes

The nitrogen atoms of a purine originate from all of the following amino acids EXCEPT

The carbon atoms of a purine originate from glycine and

Consider a cell that is provided aspartate in which all carbons are radioactively labeled.Compounds in the cell are analyzed after the biosynthesis and subsequent breakdown of pyrimidines.Which of the following compounds would display no radioactivity signal during the analysis?

Explain how the feedback inhibition of IMP dehydrogenase by GMP can increase the flux of the ATP synthesis pathway.

When analyzing the production of dTMP by thymidylate synthase in a cell-free system,which of the following compounds would be found as an additional product of this enzyme?

What would be the effect on thymidylate synthase activity if raltitrexed is present?

Which answer INCORRECTLY pairs a substrate and subsequent product of dihydropyrimidine dehydrogenase?

Which of the following is a coenzyme that is derived from ATP?

Principles of Biochemistry

Physical Biochemistry: Energy Conversion,water,and Membranes

Nucleic Acid Structure and Function

Protein Structure

Methods in Protein Biochemistry

Protein Function

Enzyme Mechanisms

Cell Signaling Systems

Glycolysis: a Paradigm of Metabolic Regulation

The Citrate Cycle

Oxidative Phosphorylation

Photosynthesis

Carbohydrate Structure and Function

Carbohydrate Metabolism

Lipid Structure and Function

Lipid Metabolism

Amino Acid Metabolism

Metabolic Integration

Dna Replication, repair, and Recombination

Rna Synthesis, processing, and Gene Silencing

Protein Synthesis, posttranslational Modification, and Transport

Gene Regulation

Filters

Two biosynthesis steps are necessary to incorporate the carbon from HCO₃ into carbamoyl aspartate.Describe the intermediate compound generated during this conversion.

Analysis of AMP and GMP synthesized in E.coli grown in medium containing ¹⁵N-labeled aspartate would show that