Question 1

Given the structure of GMP, indicate the source for all carbons and nitrogens in the guanine base.

Accepted Answer

The answer of Given the structure of GMP, indicate the...

Question 2

The end products of the pyrimidine catabolic pathway are ammonia, carbon dioxide and __________.

Accepted Answer

A) asparagine 
B) aspartic acid 
C) dihydrouracil 
D) $\beta$-alanine 
E) glutamate 
A) asparagine 
B) aspartic acid 
C) dihydrouracil 
D) $\beta$-alanine 
E) glutamate D

Question 3

Show the reaction of allopurinol with xanthine dehydrogenase and explain how this molecule functions as an inhibitor of the enzyme.

Accepted Answer

The product, alloxanthine, binds extremely tightly to the enzyme. Thus, allopurinol is a suicide substrate since once the enzyme acts upon it, it becomes almost permanently inhibited.

Question 4

Which enzyme of the pyrimidine synthesis pathway is the most highly regulated?

Accepted Answer

A) carbamoyl phosphate synthetase 
B) aspartate transcarbamoylase 
C) orotate phosphoribosyltransferase 
D) UMP kinase 
E) nucleoside diphosphate kinase 
A) carbamoyl phosphate synthetase 
B) aspartate transcarbamoylase 
C) orotate phosphoribosyltransferase 
D) UMP kinase 
E) nucleoside diphosphate kinase

Question 5

Which of the following sequence of events best explains the formation of carbamate in the mechanism of carbamoyl phosphate synthetase?

Accepted Answer

A) Bicarbonate and ATP form carboxyphosphate, then NH3 performs a nucleophilic attack on carboxyphosphate to form carbamate 
B) Bicarbonate is attacked by NH3 to produce carbamate with ATP hydrolysis occurring solely to drive the reaction to completion 
C) Bicarbonate reacts with ATP forming carboxy adenylate and pyrophosphate, then NH3 performs a nucleophilic attack on carboxy adenylate to form carbamate 
D) NH3 reacts with ATP, which then reacts with bicarbonate followed by loss of phosphate to produce carbamate 
E) none of the above 
A) Bicarbonate and ATP form carboxyphosphate, then NH3 performs a nucleophilic attack on carboxyphosphate to form carbamate 
B) Bicarbonate is attacked by NH3 to produce carbamate with ATP hydrolysis occurring solely to drive the reaction to completion 
C) Bicarbonate reacts with ATP forming carboxy adenylate and pyrophosphate, then NH3 performs a nucleophilic attack on carboxy adenylate to form carbamate 
D) NH3 reacts with ATP, which then reacts with bicarbonate followed by loss of phosphate to produce carbamate 
E) none of the above

Question 6

While endonucleases cleave nucleic acids into smaller oligonucleotides, __________ are responsible for cleaving the oligonucleotides into nucleotides.

Accepted Answer

A) phosphodiesterases 
B) nucleotidase 
C) nucleoside kinases 
D) phosphorylases 
E) phosphoribosyl transferases 
A) phosphodiesterases 
B) nucleotidase 
C) nucleoside kinases 
D) phosphorylases 
E) phosphoribosyl transferases

Question 7

What molecule contributes at least two nitrogen atoms to each purine?

Accepted Answer

A) asparagine 
B) 10-formyltetrahydrofolate 
C) glycine 
D) glutamine 
E) carbamoyl phosphate 
A) asparagine 
B) 10-formyltetrahydrofolate 
C) glycine 
D) glutamine 
E) carbamoyl phosphate

Question 8

What molecule(s)is(are)the source of the two nitrogen atoms for pyrimidine synthesis?

Accepted Answer

A) asparagine 
B) glutamine, glutamate 
C) aspartate, carbamoyl phosphate 
D) carbamoyl phosphate, glutamine 
E) aspartate, glutamate 
A) asparagine 
B) glutamine, glutamate 
C) aspartate, carbamoyl phosphate 
D) carbamoyl phosphate, glutamine 
E) aspartate, glutamate

Question 9

Which of the following is a product of xanthine dehydrogenase?

Accepted Answer

A) hypoxanthine 
B) uric acid 
C) guanine 
D) xanthosine 
E) allantoin 
A) hypoxanthine 
B) uric acid 
C) guanine 
D) xanthosine 
E) allantoin

Question 10

When ATP is bound in the activity site and ______ is bound in the specificity site, _______ will be reduced by ribonucleotide reductase.

Accepted Answer

A) ATP; ADP and GDP 
B) dATP; GDP, UDP and CDP 
C) dTTP; GDP and ADP 
D) dGTP; ADP 
E) none of the above are correct 
A) ATP; ADP and GDP 
B) dATP; GDP, UDP and CDP 
C) dTTP; GDP and ADP 
D) dGTP; ADP 
E) none of the above are correct

Question 11

Which of the following best explains the enzyme(s)involved in ribonucleotide reduction?

Accepted Answer

A) there is 1 enzyme for each of the 4 different nucleotides 
B) 1 enzyme for pyrimidine nucleotides and 1 for purine nucleotides 
C) 1 enzyme for pyrimidine nucleotides, 1 for ADP and 1 for GDP 
D) 1 enzyme for purine nucleotides, 1 for CDP and 1 for UDP 
E) 1 enzyme for all 4 nucleotides 
A) there is 1 enzyme for each of the 4 different nucleotides 
B) 1 enzyme for pyrimidine nucleotides and 1 for purine nucleotides 
C) 1 enzyme for pyrimidine nucleotides, 1 for ADP and 1 for GDP 
D) 1 enzyme for purine nucleotides, 1 for CDP and 1 for UDP 
E) 1 enzyme for all 4 nucleotides

Question 12

The following molecule is an irreversible inhibitor of which enzyme of nucleotide metabolism?

Accepted Answer

A) ribonucleotide reductase 
B) thymidylate synthase 
C) thymidine kinase 
D) dCMP deaminase 
E) CTP synthetase 
A) ribonucleotide reductase 
B) thymidylate synthase 
C) thymidine kinase 
D) dCMP deaminase 
E) CTP synthetase

Question 13

Below is the structure of 3'-azido-2',3'-dideoxythymidine (also known as AZT). Draw the structure of the metabolite of AZT that serves as the inhibitor of reverse transcriptase.

Accepted Answer

The answer of Below is the structure of 3'-azido-2',3'-dideoxythymidine (also...

Question 14

The following reaction is catalyzed by what enzyme?

Accepted Answer

A) xanthine oxidoreductase 
B) hypoxanthine hydroxylase 
C) urate oxidase 
D) guanine oxidase 
E) none of the above 
A) xanthine oxidoreductase 
B) hypoxanthine hydroxylase 
C) urate oxidase 
D) guanine oxidase 
E) none of the above

Question 15

Which of the following best explains the initial steps for the synthesis of deoxynucleotides?

Accepted Answer

A) begins with reduction of the ribose residue in PRPP 
B) deoxy PRPP is formed from deoxyribose-5-phosphate 
C) formed by reduction of ribonucleotide counterparts 
D) formed by oxidation of ribonucleotide counterparts 
E) none of the above 
A) begins with reduction of the ribose residue in PRPP 
B) deoxy PRPP is formed from deoxyribose-5-phosphate 
C) formed by reduction of ribonucleotide counterparts 
D) formed by oxidation of ribonucleotide counterparts 
E) none of the above

Question 16

The molecule below would be an analog of __________ and therefore an effective _________compound.

Accepted Answer

A) adenosine; anticancer 
B) adenosine; antiviral 
C) guanosine; anticancer 
D) guanosine; antiviral 
E) none of the above 
A) adenosine; anticancer 
B) adenosine; antiviral 
C) guanosine; anticancer 
D) guanosine; antiviral 
E) none of the above

Question 17

Which of the following correctly describes the activity or regulation of E coli ribonucleotide reductase?

Accepted Answer

A) the overall activity of the enzyme is controlled by ATP and dATP 
B) the specificity of the enzyme is controlled by all four dNTPs 
C) a tyrosine free radical participates in the reaction 
D) the reduction is not a result of simple hydride transfer 
E) all of the above 
A) the overall activity of the enzyme is controlled by ATP and dATP 
B) the specificity of the enzyme is controlled by all four dNTPs 
C) a tyrosine free radical participates in the reaction 
D) the reduction is not a result of simple hydride transfer 
E) all of the above

Question 18

The ten enzyme activities that convert PRPP to inosinic acid are part of a multienzyme complex known as the _________.

Accepted Answer

A) IMP synthetase complex 
B) purine synthetase complex 
C) purinosome 
D) tetrahydrofolate synthase complex 
E) none of the above 
A) IMP synthetase complex 
B) purine synthetase complex 
C) purinosome 
D) tetrahydrofolate synthase complex 
E) none of the above

Question 19

Which of the following correctly explains the relationship between xanthine dehydrogenase (XDH)and xanthine oxidase (XO)?

Accepted Answer

A) in healthy tissue, XDH is abundant while XO is rarely found 
B) conversion of XDH to XO occurs under conditions that damage cells 
C) XDH is converted to XO by formation of a disulfide bond 
D) XDH is converted to XO by proteolysis 
E) all of the above 
A) in healthy tissue, XDH is abundant while XO is rarely found 
B) conversion of XDH to XO occurs under conditions that damage cells 
C) XDH is converted to XO by formation of a disulfide bond 
D) XDH is converted to XO by proteolysis 
E) all of the above

Question 20

Which enzyme of the inosinic acid biosynthesis pathway is the major control point for purine synthesis?

Accepted Answer

A) phosphoribosyl pyrophosphate amidotransferase 
B) glycinamide ribonucleotide transformylase 
C) formylglycinamidine ribonucleotide amidotransferase 
D) 5-aminoimidazole ribonucleotide synthetase 
E) 5-aminoimidazole ribonucleotide carboxylase 
A) phosphoribosyl pyrophosphate amidotransferase 
B) glycinamide ribonucleotide transformylase 
C) formylglycinamidine ribonucleotide amidotransferase 
D) 5-aminoimidazole ribonucleotide synthetase 
E) 5-aminoimidazole ribonucleotide carboxylase

Exam 22: Nucleotide Metabolism

Given the structure of GMP, indicate the source for all carbons and nitrogens in the guanine base.

The end products of the pyrimidine catabolic pathway are ammonia, carbon dioxide and __________.

Show the reaction of allopurinol with xanthine dehydrogenase and explain how this molecule functions as an inhibitor of the enzyme.

Which enzyme of the pyrimidine synthesis pathway is the most highly regulated?

Which of the following sequence of events best explains the formation of carbamate in the mechanism of carbamoyl phosphate synthetase?

While endonucleases cleave nucleic acids into smaller oligonucleotides, __________ are responsible for cleaving the oligonucleotides into nucleotides.

What molecule contributes at least two nitrogen atoms to each purine?

What molecule(s)is(are)the source of the two nitrogen atoms for pyrimidine synthesis?

Which of the following is a product of xanthine dehydrogenase?

When ATP is bound in the activity site and ______ is bound in the specificity site, _______ will be reduced by ribonucleotide reductase.

Which of the following best explains the enzyme(s)involved in ribonucleotide reduction?

The following molecule is an irreversible inhibitor of which enzyme of nucleotide metabolism?

Below is the structure of 3'-azido-2',3'-dideoxythymidine (also known as AZT). Draw the structure of the metabolite of AZT that serves as the inhibitor of reverse transcriptase.

The following reaction is catalyzed by what enzyme?

Which of the following best explains the initial steps for the synthesis of deoxynucleotides?

The molecule below would be an analog of __________ and therefore an effective _________compound.

Which of the following correctly describes the activity or regulation of E coli ribonucleotide reductase?

The ten enzyme activities that convert PRPP to inosinic acid are part of a multienzyme complex known as the _________.

Which of the following correctly explains the relationship between xanthine dehydrogenase (XDH)and xanthine oxidase (XO)?

Which enzyme of the inosinic acid biosynthesis pathway is the major control point for purine synthesis?

The Scope of Biochemistry

The Matrix of Life: Weak Interactions in an Aqueous Environment

The Energetics of Life

Nucleic Acids

Introduction to Proteins: the Primary Level of Protein Structure

The Three-Dimensional Structure of Proteins

Protein Function and Evolution

Contractile Proteins and Molecular Motors

Carbohydrates: Sugars, Saccharides, Glycans

Lipids, Membranes and Cellular Transport

Enzymes: Biological Catalysts

Chemical Logic of Metabolism

Carbohydrate Metabolism: Glycolysis, Gluconeogenesis, Glycogen Metabolism, and the Pentose Phosphate Pathway

Citric Acid Cycle and Glyoxylate Cycle

Electron Transport, Oxidative Phosphorylation, and Oxygen Metabolism

Photosynthesis

Lipid Metabolism I: Fatty Acids, Triacylglycerols, and Lipoproteins

Interorgan and Intracellular Coordination of Energy Metabolism in Vertebrates

Lipid Metabolism Ii: Membrane Lipids, Steroids, Isoprenoids, and Eicosanoids

Metabolism of Nitrogenous Compounds I: Principles of Biosynthesis, Utilization, and Turnover

Metabolism of Nitogenous Compounds II: Amino Acids, Porphyrins, and Neurotransmitters

Mechanisms of Signal Transduction

Genes, Genomes and Chromosomes

DNA Replication

DNA Restructuring: Repair, Recombination, Rearrangement, Amplification

Information Readout: Transcription and Post-Transcriptional Processing

Information Decoding: Translation and Post-Translational Protein Processing

Regulation of Gene Expression

Filters

When ATP is bound in the activity site and is bound in the specificity site, _ will be reduced by ribonucleotide reductase.

The molecule below would be an analog of __ and therefore an effective _compound.