Question 1

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. 
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. C

Question 2

In mammals,CPS-II is the regulated step in pyrimidine biosynthesis.Which of the following steps in pyrimidine biosynthesis is regulated in bacteria?

Accepted Answer

A) dihydroorotase 
B) aspartate transcarbamoylase (ATCase) 
C) OMP decarboxylase 
D) dihydroorotate dehydrogenase 
A) dihydroorotase 
B) aspartate transcarbamoylase (ATCase) 
C) OMP decarboxylase 
D) dihydroorotate dehydrogenase B

Question 3

Which of the following compounds are inhibitors of purine and pyrimidine biosynthesis?

Accepted Answer

A) eicosanoids and aspirin 
B) NSAIDs and antibiotics 
C) anticancer drugs and antibiotics 
D) antibiotics and eicosanoids 
A) eicosanoids and aspirin 
B) NSAIDs and antibiotics 
C) anticancer drugs and antibiotics 
D) antibiotics and eicosanoids C

Question 4

Which of the following coenzymes responsible for 2 single-carbon additions in purine biosynthesis?

Accepted Answer

A) THF 
B) biotin 
C) SAM 
D) TPP 
A) THF 
B) biotin 
C) SAM 
D) TPP

Question 5

Which of the following compounds is the common product of purine catabolism?

Accepted Answer

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

Question 6

Which of the following characterizes the compound allopurinol?

Accepted Answer

A) It is an analog of hypoxanthine that binds tightly to xanthine oxidase and prevents uric acid formation. 
B) It is an analog of guanine that binds tightly to guanine deaminase and prevents xanthine formation. 
C) It is an analog of inosine that binds tightly to xanthine oxidase and prevents xanthine formation. 
D) It is an analog of hypoxanthine that binds tightly to guanine deaminase and prevents uric acid formation. 
A) It is an analog of hypoxanthine that binds tightly to xanthine oxidase and prevents uric acid formation. 
B) It is an analog of guanine that binds tightly to guanine deaminase and prevents xanthine formation. 
C) It is an analog of inosine that binds tightly to xanthine oxidase and prevents xanthine formation. 
D) It is an analog of hypoxanthine that binds tightly to guanine deaminase and prevents uric acid formation.

Question 7

Which of the following is the limiting substance in the biosynthesis of purines?

Accepted Answer

A) ribose-5-phosphate 
B) 5-phosphoribosyl-b-amine 
C) formylglycinamidine ribonucleotide 
D) 5-phosphoribosyl-a-pyrophosphate (PRPP) 
A) ribose-5-phosphate 
B) 5-phosphoribosyl-b-amine 
C) formylglycinamidine ribonucleotide 
D) 5-phosphoribosyl-a-pyrophosphate (PRPP)

Question 8

Which of the following statements is NOT correct concerning the regulation of the purine biosynthetic pathway?

Accepted Answer

A) PRPP competitively inhibits the enzyme Gln:PRPP amidotransferase. 
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. 
A) PRPP competitively inhibits the enzyme Gln:PRPP amidotransferase. 
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.

Question 9

Which of the following statements explains why sulfonamides are effective antibiotics?

Accepted Answer

A) They serve as analogs of p-aminobenzoic acid and block bacterial synthesis of folate. 
B) They act as inhibitors of bacterial dihydrofolate reductase,thus preventing production of tetrahydrofolate. 
C) They act as suicide substrates for the enzyme dihydropteroate synthetase. 
D) They do not affect humans because folate is a vitamin. 
A) They serve as analogs of p-aminobenzoic acid and block bacterial synthesis of folate. 
B) They act as inhibitors of bacterial dihydrofolate reductase,thus preventing production of tetrahydrofolate. 
C) They act as suicide substrates for the enzyme dihydropteroate synthetase. 
D) They do not affect humans because folate is a vitamin.

Question 10

Which of the following regarding nucleotides is correct?

Accepted Answer

A) Uridine nucleotide derivatives of carbohydrates are common intermediates in cellular transformation of carbohydrates. 
B) The nitrogenous bases serve as energy sources. 
C) Many coenzymes are derivatives of amino acids. 
D) They are produced only in eukaroytes. 
A) Uridine nucleotide derivatives of carbohydrates are common intermediates in cellular transformation of carbohydrates. 
B) The nitrogenous bases serve as energy sources. 
C) Many coenzymes are derivatives of amino acids. 
D) They are produced only in eukaroytes.

Question 11

Which of the following is NOT a substrate of carbamoyl phosphate synthetase II (CPS-II)?

Accepted Answer

A) H₂O 
B) NH₄⁺ 
C) HCO₃- 
D) glutamine 
A) H₂O 
B) NH₄⁺ 
C) HCO₃- 
D) glutamine

Question 12

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

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 2 Fe atoms that generate the free radicals. 
C) R2,but not R1,functions in the delivery of reducing equivalents. 
D) R2 homodimer carries 2 regulatory sites. 
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 2 Fe atoms that generate the free radicals. 
C) R2,but not R1,functions in the delivery of reducing equivalents. 
D) R2 homodimer carries 2 regulatory sites.

Question 13

Which of the following is NOT a characteristic of Lesch-Nyhan syndrome?

Accepted Answer

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

Question 14

Which of the following provides the immediate reducing power of ribonucleotide reductase?

Accepted Answer

A) thioredoxin 
B) ferredoxin 
C) NADH 
D) Fe-S complex 
A) thioredoxin 
B) ferredoxin 
C) NADH 
D) Fe-S complex

Question 15

Which of the following 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 resynthesis of nucleotides from bases in salvage reactions. 
D) They mediate the degradation of IMP. 
A) They are involved in the reversible reactions of purine salvage. 
B) They mediate the degradation of AMP. 
C) They are central to the resynthesis of nucleotides from bases in salvage reactions. 
D) They mediate the degradation of IMP.

Question 16

Hydrogen is often abstracted from substrates as H⁺; however,electronegative fluorine cannot be readily eliminated.Which of the following explains how enzyme inhibitors be fashioned to overcome this?

Accepted Answer

A) by replacing H with F-F at positions where catalysis involves H removal as H⁺ 
B) by replacing H with F- at positions where catalysis involves H removal as H⁺ 
C) by replacing H with F+ at positions where catalysis involves H removal as H⁺ 
D) by replacing H with F at positions where catalysis involves H removal as H⁺ 
A) by replacing H with F-F at positions where catalysis involves H removal as H⁺ 
B) by replacing H with F- at positions where catalysis involves H removal as H⁺ 
C) by replacing H with F+ at positions where catalysis involves H removal as H⁺ 
D) by replacing H with F at positions where catalysis involves H removal as H⁺

Question 17

Which of the following enzymes catalyzes the reaction to remove fumarate after aspartate has formed an amide with a carbonyl group in purine biosynthesis?

Accepted Answer

A) malate dehydrogenase 
B) citrate synthase 
C) fumarase 
D) adenylosuccinase 
A) malate dehydrogenase 
B) citrate synthase 
C) fumarase 
D) adenylosuccinase

Question 18

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

Accepted Answer

A) thyrotropin 
B) epidermal growth factor 
C) cortisol 
D) gonadotropin 
A) thyrotropin 
B) epidermal growth factor 
C) cortisol 
D) gonadotropin

Question 19

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

Accepted Answer

A) competitive inhibitor of dihydrofolate reductase 
B) competitive inhibitor of ribonucleotide reductase 
C) suicide substrate for thymidylate synthase 
D) non-competitive inhibitor of thioredoxin reductase 
A) competitive inhibitor of dihydrofolate reductase 
B) competitive inhibitor of ribonucleotide reductase 
C) suicide substrate for thymidylate synthase 
D) non-competitive inhibitor of thioredoxin reductase

Question 20

Which of the following types of bonds is formed in purine biosynthesis when glycine adds to 5-phosphoribosyl-β-amine?

Accepted Answer

A) glycosidic 
B) anhydride 
C) amine 
D) thioester 
A) glycosidic 
B) anhydride 
C) amine 
D) thioester

Exam 26: Synthesis and Degradation of Nucleotides

What is the importance of the purine nucleoside cycle?

In mammals,CPS-II is the regulated step in pyrimidine biosynthesis.Which of the following steps in pyrimidine biosynthesis is regulated in bacteria?

Which of the following compounds are inhibitors of purine and pyrimidine biosynthesis?

Which of the following coenzymes responsible for 2 single-carbon additions in purine biosynthesis?

Which of the following compounds is the common product of purine catabolism?

Which of the following characterizes the compound allopurinol?

Which of the following is the limiting substance in the biosynthesis of purines?

Which of the following statements is NOT correct concerning the regulation of the purine biosynthetic pathway?

Which of the following statements explains why sulfonamides are effective antibiotics?

Which of the following regarding nucleotides is correct?

Which of the following is NOT a substrate of carbamoyl phosphate synthetase II (CPS-II)?

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

Which of the following is NOT a characteristic of Lesch-Nyhan syndrome?

Which of the following provides the immediate reducing power of ribonucleotide reductase?

Which of the following is the function of phosphoribosyltransferases?

Hydrogen is often abstracted from substrates as H⁺; however,electronegative fluorine cannot be readily eliminated.Which of the following explains how enzyme inhibitors be fashioned to overcome this?

Which of the following enzymes catalyzes the reaction to remove fumarate after aspartate has formed an amide with a carbonyl group in purine biosynthesis?

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

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

Which of the following types of bonds is formed in purine biosynthesis when glycine adds to 5-phosphoribosyl-β-amine?

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

Filters