Question 1

In mammals CPS-II is the regulated step on pyrimidine biosynthesis; however, in bacteria ____ is the regulated step.

Accepted Answer

A)  dihydroorotase 
B)  aspartate transcarbamoylase (ATCase) 
C)  OMP decarboxylase 
D)  dehydroorotate dehydrogenase 
E)  none are true 
A)  dihydroorotase 
B)  aspartate transcarbamoylase (ATCase) 
C)  OMP decarboxylase 
D)  dehydroorotate dehydrogenase 
E)  none are true B

Question 2

How do cells salvage purines?​

Accepted Answer

Salvage pathways exist to recover free purines in useful form. Purine salvage is the only way to form purine nucleotides in some parasitic organisms. Salvage reactions involve resynthesis of nucleotides from bases via phosphoribosyltransferases.

The subsequent hydrolysis of PP_i to inorganic phosphate by pyrophosphatases renders the phosphoribosyltransferase reaction effectively irreversible. The purine phosphoribosyltransferases are adenine phosphoribosyltransferase (APRT), which mediates AMP formation, and hypoxanthine-guanine phosphoribosyltransferase (HGPRT), which can act on either hypoxanthine to form IMP or guanine to form GMP.

Question 3

Many ____ and ____ are inhibitors of purine and pyrimidine biosynthesis.

Accepted Answer

A)  eicosanoids; aspirin 
B)  NSAIDs; antibiotics 
C)  antibiotics; eicosanoids 
D)  anticancer drugs; antibiotics 
E)  anticancer drugs; eicosanoids 
A)  eicosanoids; aspirin 
B)  NSAIDs; antibiotics 
C)  antibiotics; eicosanoids 
D)  anticancer drugs; antibiotics 
E)  anticancer drugs; eicosanoids D

Question 4

Explain the regulation of pyrimidine biosynthesis in bacteria and animals.​

Accepted Answer

Pyrimidine biosynthesis in bacteria is a

Question 5

Thymidylate synthase synthesizes dTMP from ____ by ____ utilizing the coenzyme ____.

Accepted Answer

A)  dCTP; carboxylation; biotin 
B)  dUMP; methylation; THF 
C)  dCMP; methylation; THF 
D)  dGMP; phosphorylation; ATP 
E)  dUMP; phosphorylation; ATP 
A)  dCTP; carboxylation; biotin 
B)  dUMP; methylation; THF 
C)  dCMP; methylation; THF 
D)  dGMP; phosphorylation; ATP 
E)  dUMP; phosphorylation; ATP

Question 6

Discuss the regulation of the purine biosynthetic pathway after the formation of inosine monophosphate (IMP).​

Accepted Answer

The purine biosynthetic pathway splits a

Question 7

Unlike hydrogen, which is often abstracted from substrates as H+, electronegative ____ cannot be readily eliminated as ____, thus enzyme inhibitors can be fashioned in which ____ replaces H at positions where catalysis involves H-removal as H+.

Accepted Answer

A)  sodium; Na+; Na 
B)  potassium; K+; K 
C)  deuterium; D+; D 
D)  fluorine; F+; F 
E)  all are true 
A)  sodium; Na+; Na 
B)  potassium; K+; K 
C)  deuterium; D+; D 
D)  fluorine; F+; F 
E)  all are true

Question 8

​Discuss the role of thioredoxin in the synthesis of deoxynucleotides.

Accepted Answer

The immediate source of reducing equival

Question 9

All of the following are true concerning the regulation of the purine biosynthetic pathway EXCEPT:

Accepted Answer

A)  ATP is the energy source for AMP synthesis. 
B)  ADP and GDP are feedback inhibitors of ribose-5-phosphate pyrophosphokinase. 
C)  "A" and "C" nucleotides allosterically inhibit glutamine phosphoribosyl pyrophosphate amidotransferase (Gln:PRPP amidotransferase). 
D)  The rate of IMP formation is dependent on the levels of the adenine and guanine nucleotides produced. 
E)  PRPP competitively inhibits the enzyme Gln:PRPP amidotransferase. 
A)  ATP is the energy source for AMP synthesis. 
B)  ADP and GDP are feedback inhibitors of ribose-5-phosphate pyrophosphokinase. 
C)  "A" and "C" nucleotides allosterically inhibit glutamine phosphoribosyl pyrophosphate amidotransferase (Gln:PRPP amidotransferase). 
D)  The rate of IMP formation is dependent on the levels of the adenine and guanine nucleotides produced. 
E)  PRPP competitively inhibits the enzyme Gln:PRPP amidotransferase.

Question 10

Which form of the folate coenzyme is directly involved in sythesis of the purine ring?

Accepted Answer

A)  N5,N10-methenyl THF 
B)  N10-formyl THF 
C)  N5-formyl THF 
D)  tetrahydrofolate 
E)  dihydrofolate 
A)  N5,N10-methenyl THF 
B)  N10-formyl THF 
C)  N5-formyl THF 
D)  tetrahydrofolate 
E)  dihydrofolate

Question 11

The immediate reducing power of ribonucleotide reductase is provided by:

Accepted Answer

A)  thioredoxin. 
B)  Ferredoxin. 
C)  NADH. 
D)  Fe−S complex. 
E)  Cyt P-450. 
A)  thioredoxin. 
B)  Ferredoxin. 
C)  NADH. 
D)  Fe−S complex. 
E)  Cyt P-450.

Question 12

Which of the following would cause an increase in the conversion of IMP to GMP?

Accepted Answer

A)  high levels of CMP 
B)  high levels of dTTP 
C)  high levels of UMP 
D)  high levels of AMP 
E)  none of the above 
A)  high levels of CMP 
B)  high levels of dTTP 
C)  high levels of UMP 
D)  high levels of AMP 
E)  none of the above

Question 13

The fate of IMP is regulated by relative levels of ____ and ____; and energy to drive AMP synthesis is provided by ____, and energy for GMP synthesis by ____.

Accepted Answer

A)  IMP; PRPP; ATP; GTP 
B)  PRPP; ATP; ATP; GTP 
C)  AMP; ATP; GTP; ATP 
D)  AMP; GMP; GTP; ATP 
E)  IMP; GMP; ATP; GTP 
A)  IMP; PRPP; ATP; GTP 
B)  PRPP; ATP; ATP; GTP 
C)  AMP; ATP; GTP; ATP 
D)  AMP; GMP; GTP; ATP 
E)  IMP; GMP; ATP; GTP

Question 14

In purine biosynthesis when glycine adds to 5-phosphoribosyl-β-amine, the bond formed is a(n):

Accepted Answer

A)  ester. 
B)  imine. 
C)  amine. 
D)  amide. 
E)  lactam. 
A)  ester. 
B)  imine. 
C)  amine. 
D)  amide. 
E)  lactam.

Question 15

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

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. 
E)  It is subject to feed-forward activation by ADP. 
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. 
E)  It is subject to feed-forward activation by ADP.

Question 16

All of the following statements about nucleotides are true EXCEPT:

Accepted Answer

A)  They are produced by nearly all organisms. 
B)  The rate of proliferation of a cell can determine the amount of DNA and RNA synthesized per unit of time. 
C)  Uridine nucleotide derivatives of carbohydrates are common intermediates in cellular transformation of carbohydrates. 
D)  Many coenzymes are derivatives of nucleotides. 
E)  The nitrogenous bases serve as energy sources. 
A)  They are produced by nearly all organisms. 
B)  The rate of proliferation of a cell can determine the amount of DNA and RNA synthesized per unit of time. 
C)  Uridine nucleotide derivatives of carbohydrates are common intermediates in cellular transformation of carbohydrates. 
D)  Many coenzymes are derivatives of nucleotides. 
E)  The nitrogenous bases serve as energy sources.

Question 17

All are characteristics of xanthine oxidase EXCEPT:

Accepted Answer

A)  present in large amounts in liver, intestinal mucosa and milk. 
B)  uses molecular oxygen and produces H2O2. 
C)  involved in production of urea. 
D)  possesses an electron-transport chain with FAD, Fe−S cluster and molybdenum cofactor. 
E)  all are true. 
A)  present in large amounts in liver, intestinal mucosa and milk. 
B)  uses molecular oxygen and produces H2O2. 
C)  involved in production of urea. 
D)  possesses an electron-transport chain with FAD, Fe−S cluster and molybdenum cofactor. 
E)  all are true.

Question 18

About 30% of severe combined immunodeficiency syndrome (SCIDS) patients suffer from a deficiency in the activity of the enzyme ____ that is a ____-dependent enzyme and ____ deficiency can also lead to reduced immune function.

Accepted Answer

A)  HGPRT; Ca2+; Ca2+ 
B)  nucleosidase; Ca2+; Ca2+ 
C)  nucleoside phosphorylase; Pi; Pi 
D)  adenosine deaminase; Zn2+; Zn2+ 
E)  none are true 
A)  HGPRT; Ca2+; Ca2+ 
B)  nucleosidase; Ca2+; Ca2+ 
C)  nucleoside phosphorylase; Pi; Pi 
D)  adenosine deaminase; Zn2+; Zn2+ 
E)  none are true

Question 19

What is the limiting substance in the biosynthesis of purines?

Accepted Answer

A)  ribose-5-phosphate 
B)  5-phosphoribosyl-β amine 
C)  formylglycinamidine ribonucleotide 
D)  5-phosphoribosyl-α-pyrophosphate (PRPP) 
E)  α-D-ribose-5-phosphate 
A)  ribose-5-phosphate 
B)  5-phosphoribosyl-β amine 
C)  formylglycinamidine ribonucleotide 
D)  5-phosphoribosyl-α-pyrophosphate (PRPP) 
E)  α-D-ribose-5-phosphate

Question 20

What is the importance of the purine nucleoside cycle?

Accepted Answer

A)  It participates in the conversion of purines into pyrimidines. 
B)  It generates fumarate, which inhibits the formation of AMP from IMP. 
C)  It provides fumarate as an anaplerotic enhancement of the citric acid cycle. 
D)  It inhibits the citric acid cycle in skeletal muscles. 
E)  It is used in energy metabolism in the liver. 
A)  It participates in the conversion of purines into pyrimidines. 
B)  It generates fumarate, which inhibits the formation of AMP from IMP. 
C)  It provides fumarate as an anaplerotic enhancement of the citric acid cycle. 
D)  It inhibits the citric acid cycle in skeletal muscles. 
E)  It is used in energy metabolism in the liver.

Exam 26: Synthesis and Degradation of Nucleotides

In mammals CPS-II is the regulated step on pyrimidine biosynthesis; however, in bacteria ____ is the regulated step.

How do cells salvage purines?​

Many ____ and ____ are inhibitors of purine and pyrimidine biosynthesis.

Explain the regulation of pyrimidine biosynthesis in bacteria and animals.​

Thymidylate synthase synthesizes dTMP from ____ by ____ utilizing the coenzyme ____.

Discuss the regulation of the purine biosynthetic pathway after the formation of inosine monophosphate (IMP).​

Unlike hydrogen, which is often abstracted from substrates as H+, electronegative ____ cannot be readily eliminated as ____, thus enzyme inhibitors can be fashioned in which ____ replaces H at positions where catalysis involves H-removal as H+.

​Discuss the role of thioredoxin in the synthesis of deoxynucleotides.

All of the following are true concerning the regulation of the purine biosynthetic pathway EXCEPT:

Which form of the folate coenzyme is directly involved in sythesis of the purine ring?

The immediate reducing power of ribonucleotide reductase is provided by:

Which of the following would cause an increase in the conversion of IMP to GMP?

The fate of IMP is regulated by relative levels of ____ and ____; and energy to drive AMP synthesis is provided by ____, and energy for GMP synthesis by ____.

In purine biosynthesis when glycine adds to 5-phosphoribosyl-β-amine, the bond formed is a(n):

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

All of the following statements about nucleotides are true EXCEPT:

All are characteristics of xanthine oxidase EXCEPT:

About 30% of severe combined immunodeficiency syndrome (SCIDS) patients suffer from a deficiency in the activity of the enzyme ____ that is a ____-dependent enzyme and ____ deficiency can also lead to reduced immune function.

What is the limiting substance in the biosynthesis of purines?

What is the importance of the purine nucleoside cycle?

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 do cells salvage purines?

Many and are inhibitors of purine and pyrimidine biosynthesis.

Explain the regulation of pyrimidine biosynthesis in bacteria and animals.

Thymidylate synthase synthesizes dTMP from by utilizing the coenzyme .

Discuss the regulation of the purine biosynthetic pathway after the formation of inosine monophosphate (IMP).

Unlike hydrogen, which is often abstracted from substrates as H⁺, electronegative cannot be readily eliminated as , thus enzyme inhibitors can be fashioned in which replaces H at positions where catalysis involves H-removal as H⁺.

Discuss the role of thioredoxin in the synthesis of deoxynucleotides.

The fate of IMP is regulated by relative levels of and ; and energy to drive AMP synthesis is provided by , and energy for GMP synthesis by .

About 30% of severe combined immunodeficiency syndrome (SCIDS) patients suffer from a deficiency in the activity of the enzyme that is a -dependent enzyme and deficiency can also lead to reduced immune function.