Question 1

What type of reaction gives UMP from OMP?

Accepted Answer

A)  reduction 
B)  decarboxylation 
C)  oxidation 
D)  condensation 
E)  hydrolysis 
A)  reduction 
B)  decarboxylation 
C)  oxidation 
D)  condensation 
E)  hydrolysis

Question 2

Thymine nucleotides are not synthesized directly by cells but indirectly from other pyrimidine deoxyribonucleotides. All of the following statements regarding thymine nucleotide synthesis are true EXCEPT:

Accepted Answer

A)  dUMP is the immediate precursor for dTMP. 
B)  The action of dUTPase allows dUTP to serve as a substrate in DNA synthesis. 
C)  Thymidylate synthase catalyzes the formation of dTMP from dUMP. 
D)  The methyl donor in the reaction of dTMP is N5, N10-methylene-THF. 
E)  THF is used as a cofactor. 
A)  dUMP is the immediate precursor for dTMP. 
B)  The action of dUTPase allows dUTP to serve as a substrate in DNA synthesis. 
C)  Thymidylate synthase catalyzes the formation of dTMP from dUMP. 
D)  The methyl donor in the reaction of dTMP is N5, N10-methylene-THF. 
E)  THF is used as a cofactor.

Question 3

What is the common product of purine catabolism?

Accepted Answer

A)  xanthine 
B)  uric acid 
C)  inosine 
D)  hypoxanthine 
E)  xanthosine 
A)  xanthine 
B)  uric acid 
C)  inosine 
D)  hypoxanthine 
E)  xanthosine

Question 4

​How are nucleotides degraded to uric acid?

Accepted Answer

The various nucleotides are first conver

Question 5

Which of the following statements explains why methotrexate is effective as a cancer chemotherapeutic?

Accepted Answer

A)  it serves as an analog of p-aminobenzoic acid and block bacterial synthesis of folate 
B)  acts as an inhibitor of dihydrofolate reductase, thus preventing production of tetrahydrofolate 
C)  it acts as a suicide substrates for the enzyme dihydropteroate synthetase 
D)  prevents the conversion of N5,N10-methenyl THF to N10-formyl THF which is required in 2 steps of the purine synthesis pathway 
E)  both b and d are correct 
A)  it serves as an analog of p-aminobenzoic acid and block bacterial synthesis of folate 
B)  acts as an inhibitor of dihydrofolate reductase, thus preventing production of tetrahydrofolate 
C)  it acts as a suicide substrates for the enzyme dihydropteroate synthetase 
D)  prevents the conversion of N5,N10-methenyl THF to N10-formyl THF which is required in 2 steps of the purine synthesis pathway 
E)  both b and d are correct

Question 6

Allopurinol is an analog of ____ that tightly binds to ____ and prevents ____ formation.

Accepted Answer

A)  hypoxanthine; xanthine oxidase; uric acid 
B)  guanine; guanine deaminase; xanthine 
C)  inosine; xanthine oxidase; xanthine 
D)  hypoxanthine; guanine deaminase; xanthine 
E)  none of the above 
A)  hypoxanthine; xanthine oxidase; uric acid 
B)  guanine; guanine deaminase; xanthine 
C)  inosine; xanthine oxidase; xanthine 
D)  hypoxanthine; guanine deaminase; xanthine 
E)  none of the above

Question 7

Which of the following statements explains why allopurinol is able to prevent gout?

Accepted Answer

A)  it binds to uric acid thus preventing the formation of uric acid crystals 
B)  it acts as a diuretic to increase the elimination of uric acid 
C)  it inhibits the production of uric acid and allows for the more highly soluble xanthine and hypoxanthine to be excreted from the body 
D)  it stimulates the purine salvage pathway, thus eliminating the need for production of uric acid 
E)  none of the above 
A)  it binds to uric acid thus preventing the formation of uric acid crystals 
B)  it acts as a diuretic to increase the elimination of uric acid 
C)  it inhibits the production of uric acid and allows for the more highly soluble xanthine and hypoxanthine to be excreted from the body 
D)  it stimulates the purine salvage pathway, thus eliminating the need for production of uric acid 
E)  none of the above

Question 8

Enzymatic ribonucleotide reduction is accomplished via a free radical mechanism. Which of the following statements is true regarding this process?

Accepted Answer

A)  The substrate specificity site on the R1 homodimer determines if the enzyme is active or inactive. 
B)  R2 has a single active site containing two Fe atoms that generate the free radicals required for reduction. 
C)  R2, but not R1, function in the delivery of reducing equivalents. 
D)  R2 homodimer carries two regulatory sites. 
E)  A final decarboxylation forms the deoxyribonucleotide product. 
A)  The substrate specificity site on the R1 homodimer determines if the enzyme is active or inactive. 
B)  R2 has a single active site containing two Fe atoms that generate the free radicals required for reduction. 
C)  R2, but not R1, function in the delivery of reducing equivalents. 
D)  R2 homodimer carries two regulatory sites. 
E)  A final decarboxylation forms the deoxyribonucleotide product.

Question 9

Which of the following is a true statement regarding pyrimidine biosynthesis in animals?

Accepted Answer

A)  PRPP and ATP are allosteric inhibitors. 
B)  CTP is a feedback inhibitor. 
C)  It is allosterically regulated at aspartate transcarbomoylase. 
D)  UDP and UTP are feedback inhibitors of CPS-II. 
E)  ACTase catalyzes the committed step in pyrimidine synthesis. 
A)  PRPP and ATP are allosteric inhibitors. 
B)  CTP is a feedback inhibitor. 
C)  It is allosterically regulated at aspartate transcarbomoylase. 
D)  UDP and UTP are feedback inhibitors of CPS-II. 
E)  ACTase catalyzes the committed step in pyrimidine synthesis.

Question 10

Which of the following serves as an activator of CPS-II in mammals?

Accepted Answer

A)  thyrotropin 
B)  epidermal growth factor 
C)  cortisol 
D)  gonadotropin 
E)  none of the above 
A)  thyrotropin 
B)  epidermal growth factor 
C)  cortisol 
D)  gonadotropin 
E)  none of the above

Question 11

Which of the following serves as one of the nitrogen sources for the pyrimidine ring?

Accepted Answer

A)  glutamate 
B)  carbamoyl phosphate 
C)  asparagine 
D)  glycine 
E)  none of the above 
A)  glutamate 
B)  carbamoyl phosphate 
C)  asparagine 
D)  glycine 
E)  none of the above

Question 12

What is the function of phosphoribosyltransferases?

Accepted Answer

A)  they are involved in the reversible reactions of purine salvage. 
B)  they mediate the degradation of AMP. 
C)  they are central to the re-synthesis of nucleotides from bases in salvage reactions. 
D)  they mediate the degradation of IMP. 
E)  they are competitive inhibitors employed in the salvage of purine nucleotides. 
A)  they are involved in the reversible reactions of purine salvage. 
B)  they mediate the degradation of AMP. 
C)  they are central to the re-synthesis of nucleotides from bases in salvage reactions. 
D)  they mediate the degradation of IMP. 
E)  they are competitive inhibitors employed in the salvage of purine nucleotides.

Question 13

All are substrates of carbamoyl phosphate synthetase II (CPS-II) EXCEPT:

Accepted Answer

A)  H2O. 
B)  NH4+. 
C)  HCO3−. 
D)  glutamine. 
E)  2ATP. 
A)  H2O. 
B)  NH4+. 
C)  HCO3−. 
D)  glutamine. 
E)  2ATP.

Question 14

The reaction, base + PRPP → nucleoside-5-phosphate + PPi is catalyzed by the enzyme:

Accepted Answer

A)  nucleotide diphosphate kinase. 
B)  phosphoribosyltransferase. 
C)  ribose-5-phosphate pyrophosphokinase. 
D)  adenylate kinase. 
E)  GMP synthetase. 
A)  nucleotide diphosphate kinase. 
B)  phosphoribosyltransferase. 
C)  ribose-5-phosphate pyrophosphokinase. 
D)  adenylate kinase. 
E)  GMP synthetase.

Question 15

Which of the following is a source of 2 carbon atoms of the purine ring system?

Accepted Answer

A)  aspartate 
B)  carbon dioxide 
C)  glycine 
D)  glutamine 
E)  glutamic acid 
A)  aspartate 
B)  carbon dioxide 
C)  glycine 
D)  glutamine 
E)  glutamic acid

Question 16

The coenzyme for two single carbon additions in purine biosynthesis is:

Accepted Answer

A)  THF. 
B)  biotin. 
C)  SAM. 
D)  TPP. 
E)  none are true. 
A)  THF. 
B)  biotin. 
C)  SAM. 
D)  TPP. 
E)  none are true.

Question 17

Which of the following is an advantage of metabolic channeling?

Accepted Answer

A)  It allows the product of one reaction to be available for a reaction later in another pathway. 
B)  It allows the diffusion of substrates. 
C)  It allows the dilution of substrates. 
D)  It allows a more diverse interaction of substrates, intermediates, and enzymes. 
E)  It does not allow for substrate dilution into the milieu and for the accumulation of intermediates. 
A)  It allows the product of one reaction to be available for a reaction later in another pathway. 
B)  It allows the diffusion of substrates. 
C)  It allows the dilution of substrates. 
D)  It allows a more diverse interaction of substrates, intermediates, and enzymes. 
E)  It does not allow for substrate dilution into the milieu and for the accumulation of intermediates.

Question 18

Which of the following is the mechanism of action of 5-fluorouracil?

Accepted Answer

A)  competitive inhibitor of dihydrofolate reductase 
B)  suicide substrate for thymidylate synthase 
C)  competitive inhibitor of ribonucleotide reductase 
D)  non-competitive inhibitor of thioredoxin reductase 
E)  none of the above 
A)  competitive inhibitor of dihydrofolate reductase 
B)  suicide substrate for thymidylate synthase 
C)  competitive inhibitor of ribonucleotide reductase 
D)  non-competitive inhibitor of thioredoxin reductase 
E)  none of the above

Question 19

Adenylosuccinase (adenylosuccinate lyase) catalyzes the reaction to remove ____ after ____ has formed an amide with a carbonyl group in purine biosynthesis.

Accepted Answer

A)  succinate; glutamate 
B)  succinate; aspartate 
C)  fumarate; alanine 
D)  fumarate; aspartate 
E)  α-ketoglutarate; glutamate 
A)  succinate; glutamate 
B)  succinate; aspartate 
C)  fumarate; alanine 
D)  fumarate; aspartate 
E)  α-ketoglutarate; glutamate

Question 20

All are characteristics of Lesch-Nyhan Syndrome EXCEPT:

Accepted Answer

A)  gouty arthritis due to excessive uric acid accumulation 
B)  severe malfunctions of the nervous system 
C)  complete deficiency in HGPRT activity 
D)  congenital, recessive, sex-linked trait manifested only in males 
E)  all are true 
A)  gouty arthritis due to excessive uric acid accumulation 
B)  severe malfunctions of the nervous system 
C)  complete deficiency in HGPRT activity 
D)  congenital, recessive, sex-linked trait manifested only in males 
E)  all are true

Exam 26: Synthesis and Degradation of Nucleotides

What type of reaction gives UMP from OMP?

Thymine nucleotides are not synthesized directly by cells but indirectly from other pyrimidine deoxyribonucleotides. All of the following statements regarding thymine nucleotide synthesis are true EXCEPT:

What is the common product of purine catabolism?

​How are nucleotides degraded to uric acid?

Which of the following statements explains why methotrexate is effective as a cancer chemotherapeutic?

Allopurinol is an analog of ____ that tightly binds to ____ and prevents ____ formation.

Which of the following statements explains why allopurinol is able to prevent gout?

Enzymatic ribonucleotide reduction is accomplished via a free radical mechanism. Which of the following statements is true regarding this process?

Which of the following is a true statement regarding pyrimidine biosynthesis in animals?

Which of the following serves as an activator of CPS-II in mammals?

Which of the following serves as one of the nitrogen sources for the pyrimidine ring?

What is the function of phosphoribosyltransferases?

All are substrates of carbamoyl phosphate synthetase II (CPS-II) EXCEPT:

The reaction, base + PRPP → nucleoside-5-phosphate + PPi is catalyzed by the enzyme:

Which of the following is a source of 2 carbon atoms of the purine ring system?

The coenzyme for two single carbon additions in purine biosynthesis is:

Which of the following is an advantage of metabolic channeling?

Which of the following is the mechanism of action of 5-fluorouracil?

Adenylosuccinase (adenylosuccinate lyase) catalyzes the reaction to remove ____ after ____ has formed an amide with a carbonyl group in purine biosynthesis.

All are characteristics of Lesch-Nyhan Syndrome EXCEPT:

The Facts of Life: Chemistry Is the Logic of Biological Phenomena

Water: the Medium of Life

Thermodynamics of Biological Systems

Amino Acids and the Peptide Bond

Proteins: Their Primary Structure and Biological Functions

Proteins: Secondary, Tertiary, and Quaternary Structure

Carbohydrates and the Glycoconjugates of Cell Surfaces

Lipids

Membranes and Membrane Transport

Nucleotides and Nucleic Acids

Structure of Nucleic Acids

Recombinant Dna, Cloning, Chimeric Genes, and Synthetic Biology

Enzymeskinetics and Specificity

Mechanisms of Enzyme Action

Enzyme Regulation

Molecular Motors

Metabolism: an Overview

Glycolysis

The Tricarboxylic Acid Cycle

Electron Transport and Oxidative Phosphorylation

Photosynthesis

Gluconeogenesis, Glycogen Metabolism, and the Pentose Phosphate Pathway

Fatty Acid Catabolism

Lipid Biosynthesis

Nitrogen Acquisition and Amino Acid Metabolism

Metabolic Integration and Organ Specialization

Dna Metabolism: Replication, Recombination, and Repair

Transcription and the Regulation of Gene Expression

Protein Synthesis

Completing the Protein Life Cycle: Folding, Processing, and Degradation

The Reception and Transmission of Extracellular Information

Filters

How are nucleotides degraded to uric acid?

Allopurinol is an analog of that tightly binds to and prevents formation.

The reaction, base + PRPP → nucleoside-5-phosphate + PP_i is catalyzed by the enzyme:

Adenylosuccinase (adenylosuccinate lyase) catalyzes the reaction to remove after has formed an amide with a carbonyl group in purine biosynthesis.