Question 1

Which of the following enzymes catalyzes this reaction?
Base + PRPP → nucleoside-5-phosphate + PPᵢ

Accepted Answer

A) nucleotide diphosphate kinase 
B) phosphoribosyltransferase 
C) ribose-5-phosphate pyrophosphokinase 
D) adenylate kinase 
A) nucleotide diphosphate kinase 
B) phosphoribosyltransferase 
C) ribose-5-phosphate pyrophosphokinase 
D) adenylate kinase

Question 2

Glutamine phosphoribosyl pyrophosphate amidotransferase catalyzes step 2 in the biosynthesis of purines.Which of the following regarding the regulation of this enzyme is correct?

Accepted Answer

A) It is accelerated by an input of ATP or GTP. 
B) It is sensitive to activation by azaserine. 
C) It is accelerated by an input of AMP or GMP. 
D) The G series of nucleotides as well as the adenine nucleotides act as competitive inhibitors. 
A) It is accelerated by an input of ATP or GTP. 
B) It is sensitive to activation by azaserine. 
C) It is accelerated by an input of AMP or GMP. 
D) The G series of nucleotides as well as the adenine nucleotides act as competitive inhibitors.

Question 3

Which of the following is characteristic characteristic of xanthine oxidase?

Accepted Answer

A) present in small amounts in liver,intestinal mucosa,and milk 
B) uses H₂O₂ to produce molecular oxygen 
C) possesses an electron-transport chain with FAD,Fe-S cluster,and molybdenum cofactor 
D) involved in production of urea 
A) present in small amounts in liver,intestinal mucosa,and milk 
B) uses H₂O₂ to produce molecular oxygen 
C) possesses an electron-transport chain with FAD,Fe-S cluster,and molybdenum cofactor 
D) involved in production of urea

Question 4

Which of the following regarding pyrimidine biosynthesis in animals is correct?

Accepted Answer

A) PRPP and ATP are allosteric inhibitors. 
B) CTP is a feedback inhibitor. 
C) ATCase catalyzes the committed step in pyrimidine synthesis. 
D) UDP and UTP are feedback inhibitors of CPS-II. 
A) PRPP and ATP are allosteric inhibitors. 
B) CTP is a feedback inhibitor. 
C) ATCase catalyzes the committed step in pyrimidine synthesis. 
D) UDP and UTP are feedback inhibitors of CPS-II.

Question 5

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

Accepted Answer

A) Allopurinol binds to uric acid,thus preventing the formation of uric acid crystals. 
B) Allopurinol acts as a diuretic to increase the elimination of uric acid. 
C) Allopurinol inhibits the production of uric acid and allows for the more highly soluble xanthine and hypoxanthine to be excreted from the body. 
D) Allopurinol stimulates the purine salvage pathway,thus eliminating the need for production of uric acid. 
A) Allopurinol binds to uric acid,thus preventing the formation of uric acid crystals. 
B) Allopurinol acts as a diuretic to increase the elimination of uric acid. 
C) Allopurinol inhibits the production of uric acid and allows for the more highly soluble xanthine and hypoxanthine to be excreted from the body. 
D) Allopurinol stimulates the purine salvage pathway,thus eliminating the need for production of uric acid.

Question 6

Which of the following mechanisms explains how thymidylate synthase synthesizes dTMP from dUMP?

Accepted Answer

A) by methylation utilizing the coenzyme biotin 
B) by carboxylation utilizing the coenzyme THF 
C) by phosphorylation utilizing the coenzyme ATP 
D) by reduction utilizing the coenzyme ATP 
A) by methylation utilizing the coenzyme biotin 
B) by carboxylation utilizing the coenzyme THF 
C) by phosphorylation utilizing the coenzyme ATP 
D) by reduction utilizing the coenzyme ATP

Question 7

Which of the following is an advantage of metabolic channelling?

Accepted Answer

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

Question 8

Which of the following types of reactions gives UMP from OMP?

Accepted Answer

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

Question 9

Which of the following enzyme activities is deficient in about 30% of severe combined immunodeficiency syndrome (SCIDS)patients?

Accepted Answer

A) HGPRT 
B) nucleosidase 
C) nucleoside phosphorylase 
D) adenosine deaminase 
A) HGPRT 
B) nucleosidase 
C) nucleoside phosphorylase 
D) adenosine deaminase

Question 10

Thymine nucleotides are not synthesized directly by cells but indirectly from other pyrimidine deoxyribonucleotides.Which of these statements is NOT correct regarding thymine nucleotide synthesis?

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) The methyl donor in the reaction of dTMP is N5,N10-methylene-THF. 
D) 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) The methyl donor in the reaction of dTMP is N5,N10-methylene-THF. 
D) THF is used as a cofactor.

Question 11

Which of the following factors regulates the fate of IMP?

Accepted Answer

A) the relative levels of PRPP and GTP 
B) the relative levels of PRPP and ATP 
C) the relative levels of ATP and GTP 
D) the relative levels of AMP and GMP 
A) the relative levels of PRPP and GTP 
B) the relative levels of PRPP and ATP 
C) the relative levels of ATP and GTP 
D) the relative levels of AMP and GMP

Question 12

Which of the following is a result of high ATP levels with respect to the regulation of ribonucleotide reductase?

Accepted Answer

A) an increase in the concentration of dADP 
B) decreased dTTP concentration 
C) oxidation of UDP and CDP to dUDP and dCDP 
D) a rise in dGTP levels 
A) an increase in the concentration of dADP 
B) decreased dTTP concentration 
C) oxidation of UDP and CDP to dUDP and dCDP 
D) a rise in dGTP levels

Exam 26: Synthesis and Degradation of Nucleotides

Which of the following enzymes catalyzes this reaction? Base + PRPP → nucleoside-5-phosphate + PPᵢ

Glutamine phosphoribosyl pyrophosphate amidotransferase catalyzes step 2 in the biosynthesis of purines.Which of the following regarding the regulation of this enzyme is correct?

Which of the following is characteristic characteristic of xanthine oxidase?

Which of the following regarding pyrimidine biosynthesis in animals is correct?

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

Which of the following mechanisms explains how thymidylate synthase synthesizes dTMP from dUMP?

Which of the following is an advantage of metabolic channelling?

Which of the following types of reactions gives UMP from OMP?

Which of the following enzyme activities is deficient in about 30% of severe combined immunodeficiency syndrome (SCIDS)patients?

Thymine nucleotides are not synthesized directly by cells but indirectly from other pyrimidine deoxyribonucleotides.Which of these statements is NOT correct regarding thymine nucleotide synthesis?

Which of the following factors regulates the fate of IMP?

Which of the following is a result of high ATP levels with respect to the regulation of ribonucleotide reductase?

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

Water: the Medium of Life

Thermodynamics of Biological Systems

Amino Acids

Proteins: Their Primary Structure and Biological Functions

Proteins: Secondary, tertiary, and Quaternary Structure

Carbohydrates and the Glycoconjugates of Cell Surfaces

Lipids

Lipid Biosynthesis

Membranes and Membrane Transport

The Reception and Transmission of Extracellular Information

Enzymes Kinetics and Specificity

Mechanisms of Enzyme Action

Enzyme Regulation

Molecular Motors

Nutrition and the Organization of Metabolism

Glycolysis

The Tricarboxylic Acid Cycle

Electron Transport and Oxidative Phosphorylation

Photosynthesis

Gluconeogenesis, glycogen Metabolism, and the Pentose Phosphate Pathway

Fatty Acid Catabolism

Nitrogen Acquisition and Amino Acid Metabolism

Nucleotides and Nucleic Acids

Structure of Nucleic Acids

Recombinant Dna: Cloning and Creation of Chimeric Genes

DNA Metabolism: Replication, recombination, and Repair

Transcription and the Regulation of Gene Expression

Protein Synthesis

Post-Transcriptional Regulation of Gene Expression

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

Metabolic Integration and Organ Specialization

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