Question 1

Which are purines?

Accepted Answer

A)  adenine and thymine 
B)  guanine and adenine 
C)  cytosine and thymine 
D)  uracil and guanine 
A)  adenine and thymine 
B)  guanine and adenine 
C)  cytosine and thymine 
D)  uracil and guanine

Question 2

The pyrimidine ring system is shown below. What is the source of the N-1 during the de novo biosynthesis of pyrimidines?

Accepted Answer

A)  aspartate 
B)  urea 
C)  asparagine 
D)  IMP 
A)  aspartate 
B)  urea 
C)  asparagine 
D)  IMP

Question 3

During de novo biosynthesis of the purine nucleotides, the purine ring is first formed as a free base before being attached to the ribose 5-phosphate moiety.

Accepted Answer

A) True 
 B)False

Question 4

Allopurinol may be used to treat gout due to an excess of uric acid production because it can be converted to oxypurinol by , and oxypurinol strongly inhibits .

Accepted Answer

A)  xanthine oxidase; urease 
B)  urease; xanthine oxidase 
C)  xanthine oxidase; xanthine oxidase 
D)  urease; urease 
E)  xanthine oxidase; sodium urate 
A)  xanthine oxidase; urease 
B)  urease; xanthine oxidase 
C)  xanthine oxidase; xanthine oxidase 
D)  urease; urease 
E)  xanthine oxidase; sodium urate

Question 5

The first nucleotide product in the de novo biosynthetic pathway of purines is

Accepted Answer

A)  AMP. 
B)  GMP. 
C)  IMP. 
D)  XMP. 
A)  AMP. 
B)  GMP. 
C)  IMP. 
D)  XMP.

Question 6

Which type of enzymes catalyze the phosphorylation of dADP, dGDP and dCDP?

Accepted Answer

A)  nucleotide phosphorylases 
B)  nucleoside diphosphate kinases 
C)  triphosphatases 
D)  deoxyribosylphosphatases 
A)  nucleotide phosphorylases 
B)  nucleoside diphosphate kinases 
C)  triphosphatases 
D)  deoxyribosylphosphatases

Question 7

The reduction of ribonucleotides by ribonucleotide reductase requires the formation of a/an .

Accepted Answer

A)  covalent intermediate 
B)  free radical protein 
C)  intermediate methyl group 
D)  acid-base catalyst 
A)  covalent intermediate 
B)  free radical protein 
C)  intermediate methyl group 
D)  acid-base catalyst

Question 8

Which is the correct order for the synthesis of CTP?

Accepted Answer

A)  UMP → UDP→ UTP → CTP 
B)  GMP → GDP→ GTP → CTP 
C)  UTP → TTP→ CTP 
D)  UMP → CMP→ CDP → CTP 
A)  UMP → UDP→ UTP → CTP 
B)  GMP → GDP→ GTP → CTP 
C)  UTP → TTP→ CTP 
D)  UMP → CMP→ CDP → CTP

Question 9

The first step in the de novo biosynthesis of IMP is a reaction between glutamine and PRPP. Which statement is not true about this reaction?

Accepted Answer

A)  An amine group is attached to the anomeric carbon atom of the ribose ring. 
B)  The configuration of the anomeric carbon atom is inverted from β to α. 
C)  A pyrophosphate is lost from PRPP. 
D)  The reaction is catalyzed by glutamine-PRPP aminotransferase. 
A)  An amine group is attached to the anomeric carbon atom of the ribose ring. 
B)  The configuration of the anomeric carbon atom is inverted from β to α. 
C)  A pyrophosphate is lost from PRPP. 
D)  The reaction is catalyzed by glutamine-PRPP aminotransferase.

Question 10

The ribonucleotides that are reduced to deoxyribonucleotides in most organisms are .

Accepted Answer

A)  nucleosides 
B)  mononucleotides 
C)  dinucleotides 
D)  trinucleotides 
A)  nucleosides 
B)  mononucleotides 
C)  dinucleotides 
D)  trinucleotides

Question 11

Which structure below is PRPP?

Accepted Answer

A)  I 
B)  II 
C)  III 
D)  IV 
A)  I 
B)  II 
C)  III 
D)  IV

Question 12

In the reactions catalyzed by xanthine oxidase, electrons are transferred to to form .

Accepted Answer

A)  O2; H2O2  
B)  H2O2; O2  
C)  H2O; O2  
D)  O2; H2O 
A)  O2; H2O2  
B)  H2O2; O2  
C)  H2O; O2  
D)  O2; H2O

Question 13

Which enzyme catalyzes the step in purine nucleotide biosynthesis that is the principal site of regulation for the pathway?

Accepted Answer

A)  adenylsuccinate lyase 
B)  OPM decarboxylase 
C)  IMP cyclohydrolase 
D)  glutamine-PRPP amidotransferase 
A)  adenylsuccinate lyase 
B)  OPM decarboxylase 
C)  IMP cyclohydrolase 
D)  glutamine-PRPP amidotransferase

Question 14

Which is the source of the ribose ring in purine nucleotides?

Accepted Answer

A)  ATP 
B)  AMP 
C)  PRPP 
D)  cGDP 
A)  ATP 
B)  AMP 
C)  PRPP 
D)  cGDP

Question 15

The pyrimidine ring system is shown below. What is the source of the N-3 during the de novo biosynthesis of pyrimidines?

Accepted Answer

A)  ammonia 
B)  glutamine 
C)  arginine 
D)  urea 
A)  ammonia 
B)  glutamine 
C)  arginine 
D)  urea

Question 16

The source of the hydrogen to form water during the reduction of nucleoside triphosphates is .

Accepted Answer

A)  thioredoxin 
B)  NADP 
C)  NADH 
D)  NADPH 
E)  FADH2 
A)  thioredoxin 
B)  NADP 
C)  NADH 
D)  NADPH 
E)  FADH2

Question 17

Which is a common precursor in the de novo synthesis of purine nucleotides?

Accepted Answer

A)  inosine 5ʹ-monophosphate 
B)  xanthosine monophosphate 
C)  orotate 
D)  adenylosuccinate 
A)  inosine 5ʹ-monophosphate 
B)  xanthosine monophosphate 
C)  orotate 
D)  adenylosuccinate

Question 18

The purine ring system is shown below. What is the source of the N-1 atom during de novo biosynthesis of purines?

Accepted Answer

A)  glycine 
B)  glutamine 
C)  aspartate 
D)  arginine 
A)  glycine 
B)  glutamine 
C)  aspartate 
D)  arginine

Question 19

The conversion of UTP to CTP involves .

Accepted Answer

A)  hydrolysis of a phosphate group 
B)  oxidation of an OH group 
C)  transfer of an NH2 group 
D)  formation of a carbon-carbon double bond 
A)  hydrolysis of a phosphate group 
B)  oxidation of an OH group 
C)  transfer of an NH2 group 
D)  formation of a carbon-carbon double bond

Question 20

Four of the ten enzymes required for the biosynthesis of IMP are listed below. In which order do the reactions these enzymes catalyze occur during the synthesis of IMP? 1. IMP cyclohydrolase
2. GAR synthase
3. glutamine-PRPP amidotransferase
4. AIR carboxylase

Accepted Answer

A)  1 → 2 → 3 → 4 
B)  4 → 3 → 2 → 1 
C)  3 → 2 → 4 → 1 
D)  2 → 3 → 4 → 1 
A)  1 → 2 → 3 → 4 
B)  4 → 3 → 2 → 1 
C)  3 → 2 → 4 → 1 
D)  2 → 3 → 4 → 1

Exam 18: Nucleotide Metabolism

Which are purines?

The pyrimidine ring system is shown below. What is the source of the N-1 during the de novo biosynthesis of pyrimidines?

During de novo biosynthesis of the purine nucleotides, the purine ring is first formed as a free base before being attached to the ribose 5-phosphate moiety.

Allopurinol may be used to treat gout due to an excess of uric acid production because it can be converted to oxypurinol by , and oxypurinol strongly inhibits .

The first nucleotide product in the de novo biosynthetic pathway of purines is

Which type of enzymes catalyze the phosphorylation of dADP, dGDP and dCDP?

The reduction of ribonucleotides by ribonucleotide reductase requires the formation of a/an .

Which is the correct order for the synthesis of CTP?

The first step in the de novo biosynthesis of IMP is a reaction between glutamine and PRPP. Which statement is not true about this reaction?

The ribonucleotides that are reduced to deoxyribonucleotides in most organisms are .

Which structure below is PRPP?

In the reactions catalyzed by xanthine oxidase, electrons are transferred to to form .

Which enzyme catalyzes the step in purine nucleotide biosynthesis that is the principal site of regulation for the pathway?

Which is the source of the ribose ring in purine nucleotides?

The pyrimidine ring system is shown below. What is the source of the N-3 during the de novo biosynthesis of pyrimidines?

The source of the hydrogen to form water during the reduction of nucleoside triphosphates is .

Which is a common precursor in the de novo synthesis of purine nucleotides?

The purine ring system is shown below. What is the source of the N-1 atom during de novo biosynthesis of purines?

The conversion of UTP to CTP involves .

Four of the ten enzymes required for the biosynthesis of IMP are listed below. In which order do the reactions these enzymes catalyze occur during the synthesis of IMP? 1. IMP cyclohydrolase 2. GAR synthase 3. glutamine-PRPP amidotransferase 4. AIR carboxylase

Introduction to Biochemistry

Water

Amino Acids and the Primary Structures of Proteins

Proteins: Three-Dimensional Structure and Function

Properties of Enzymes

Mechanisms of Enzymes

Coenzymes and Vitamins

Carbohydrates

Lipids and Membranes

Introduction to Metabolism

Glycolysis

Gluconeogenesis, the Pentose Phosphate Pathway, and Glycogen Metabolism

The Citric Acid Cycle

Electron Transport and Oxidative Phosphorylation

Photosynthesis

Lipid Metabolism

Amino Acid Metabolism

Nucleic Acids

Dna Replication, Repair, and Recombination

Transcription and Rna Processing

Protein Synthesis

Recombinant Dna Technology

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