Question 1

Order the following steps involving the regeneration of ribonucleotide reductase that occurs in most animals so that it may carry out the formation of deoxyribonucleotides. (Note that not all steps are shown.) 1. Reduction of thioredoxin
2) Reduction of ribonucleotide reductase
3) Oxidation of thioredoxin reductase
4) Reduction of thioredoxin reductase

Accepted Answer

The answer of Order the following steps involving the regeneration...

Question 2

Which answer INCORRECTLY pairs a substrate and subsequent product of dihydropyrimidine dehydrogenase?

Accepted Answer

Dihydropyrimidine dehydrogenase is not involved in the catabolism of adenine, so dihydroadenine is not a correct product. A, B, and D are correct pairings of substrates and products for dihydropyrimidine dehydrogenase.

Question 3

To purify glutathione reductase to carry out a kinetics analysis, which organism would be the best source of the enzyme?

Accepted Answer

E. coli is a commonly used organism for protein expression and purification, making it the most practical choice for obtaining large quantities of glutathione reductase for kinetics analysis. The other organisms may also produce the enzyme, but may be less accessible or yield less protein.

Question 4

Complete the following pathway of the degradation of UMP. UMP $\rightarrow$ Uridine $\rightarrow$ __________ $\rightarrow$ Dihydrouracil $\rightarrow$ NH₄⁺+ HCO₃- + $\beta$-alanine

Accepted Answer

The degradation pathway of UMP involves the conversion of uridine to uracil, which is then converted to dihydrouracil, and finally to NH₄⁺, HCO₃⁻, and β-alanine.

Question 5

Consider a cell that is provided aspartate in which all carbons are radioactively labeled. Compounds in the cell are analyzed after the biosynthesis and subsequent breakdown of pyrimidines. Which of the following compounds would display no radioactivity signal during the analysis?

Accepted Answer

Glutamine is not derived from aspartate in the biosynthesis or breakdown of pyrimidines, so it would not display radioactivity if only the aspartate carbons were labeled.

Question 6

CTP synthetase is inhibited by __________ and activated by _.

Accepted Answer

CTP synthetase is feedback inhibited by its product CTP (cytidine triphosphate) and is activated by the presence of GTP (guanosine triphosphate).

Question 7

The chemotherapy agent 5-fluorouracil is usually degraded by which of the following enzymes, which requires administration of higher doses?

Accepted Answer

5-fluorouracil is degraded by dihydropyrimidine dehydrogenase, which requires higher doses of the drug for sufficient metabolism. Option A is a fabricated enzyme name and option B is actually involved in activating 5-fluorouracil. Option D is not involved in the degradation of 5-fluorouracil.

Question 8

$\beta$-aminoisobutyrate is a breakdown product of

Accepted Answer

The answer of $\beta$-aminoisobutyrate is a breakdown product of
...

Question 9

How many ATP are converted to ADP during the biosynthesis of CTP from UMP?

Accepted Answer

The answer of How many ATP are converted to ADP...

Question 10

What is the name of the compound below, which is an intermediate in the breakdown of some pyrimidines?

Accepted Answer

The compound shown is N-carbamoyl-beta-alanine, which is an intermediate in the breakdown of some pyrimidines. Choice A is incorrect because it includes the incorrect amino acid (alanine instead of beta-alanine). Choice C is incorrect because it shows a different compound altogether (dihydrothymine). Choice D is incorrect because it does not include the "N-carbamoyl" portion of the name.

Question 11

Dihydropyrimidine dehydrogenase deficiencies exist in approximately of humans and can result in complications when 5-fluorouracil is administered as a therapy.

Accepted Answer

Dihydropyrimidine dehydrogenase deficiency affects approximately 5% of the population and can lead to severe toxic reactions when patients are treated with the chemotherapy drug 5-fluorouracil (5-FU), which is commonly used in cancer treatment.

Question 12

An oncologist has a patient with dihydropyrimidine dehydrogenase deficiency. Which of the following is a chemotherapy agent that the doctor should be cautious about using with this patient because of serious side effects?

Accepted Answer

Patients with dihydropyrimidine dehydrogenase deficiency have a higher risk of serious side effects, including life-threatening toxicity, when treated with chemotherapy agents like 5-fluorouracil. Therefore, the oncologist should be cautious about using this drug with the patient.

Question 13

Dihydropyrimidine dehydrogenase deficiencies can lead to an intolerance of high doses of 5-fluorouracil because 5-fluorouracil dihydropyrimidine dehydrogenase.

Accepted Answer

Dihydropyrimidine dehydrogenase is the enzyme primarily responsible for the metabolism of 5-fluorouracil. Deficiencies in this enzyme can lead to an accumulation of 5-fluorouracil in the body, causing toxicity.

Question 14

Consider the breakdown of the four compounds below. Which would be expected to generate $\beta$-alanine?

Accepted Answer

dCMP (deoxycytidine monophosphate) breakdown can generate F1F1F1S1βF1F1F10-alanine, as it is a nucleotide that, upon degradation, can lead to the formation of this compound through its connection to pyrimidine metabolism.

Question 15

To determine the role of glutaredoxin in the generation of deoxyribonucleotides by ribonucleotide reductase, which organisms would be the best to study?

Accepted Answer

Glutaredoxin is a small protein that contains a conserved active site cysteine residue that functions as a disulfide reductase. It has been shown to have a role in the maturation and activation of bacterial ribonucleotide reductase, which catalyzes the conversion of ribonucleotides to deoxyribonucleotides. Therefore, studying glutaredoxin in bacteria would be the best choice to investigate its role in this process.

Question 16

The biosynthesis of CTP is allosterically regulated at many steps. Which of the following is a major point of regulation?

Accepted Answer

The answer of The biosynthesis of CTP is allosterically regulated...

Question 17

How many PRPP are required to synthesize two UMP and two CTP from carbamoyl aspartate?

Accepted Answer

Carbamoyl aspartate is a precursor to the synthesis of Uridine Monophosphate (UMP) and Cytidine Triphosphate (CTP). The process of synthesizing UMP and CTP from carbamoyl aspartate requires 4 molecules of Phosphoribosyl pyrophosphate (PRPP). Therefore, the correct answer is C) 4.

Question 18

Tyr122 is important in the mechanism of the E. coli ribonucleotide reductase. The function of this amino acid in the mechanism is to

Accepted Answer

Tyr122 is important in the mechanism of the E. coli ribonucleotide reductase because it is responsible for generating the Cys439 radical species, which is necessary for the conversion of ribonucleotides to deoxyribonucleotides.

Question 19

A mutation in may alter the rate at which UT is converted to CTP.

Accepted Answer

CTP synthetase is the enzyme responsible for converting UTP (uridine triphosphate) to CTP (cytidine triphosphate), thus a mutation in this enzyme could alter the rate of this conversion.

Question 20

The biosynthesis of deoxynucleosides is important, yet different organisms require different sets of enzymes to carry it out. If 100 different species were analyzed, which enzyme is most likely to be found in all of them?

Accepted Answer

Ribonucleotide reductase is a universally conserved enzyme that plays a crucial role in the biosynthesis of deoxynucleosides in all organisms, making it the most likely enzyme to be found in all 100 different species. Thioredoxin, glutaredoxin, and glutathione reductase, on the other hand, are not as universally conserved and are only present in certain groups of organisms.

Quiz 18: Nucleotide Metabolism

Which answer INCORRECTLY pairs a substrate and subsequent product of dihydropyrimidine dehydrogenase?

To purify glutathione reductase to carry out a kinetics analysis, which organism would be the best source of the enzyme?

Consider a cell that is provided aspartate in which all carbons are radioactively labeled. Compounds in the cell are analyzed after the biosynthesis and subsequent breakdown of pyrimidines. Which of the following compounds would display no radioactivity signal during the analysis?

CTP synthetase is inhibited by __________ and activated by _.

The chemotherapy agent 5-fluorouracil is usually degraded by which of the following enzymes, which requires administration of higher doses?

$\beta$ -aminoisobutyrate is a breakdown product of

How many ATP are converted to ADP during the biosynthesis of CTP from UMP?

Dihydropyrimidine dehydrogenase deficiencies exist in approximately of humans and can result in complications when 5-fluorouracil is administered as a therapy.

An oncologist has a patient with dihydropyrimidine dehydrogenase deficiency. Which of the following is a chemotherapy agent that the doctor should be cautious about using with this patient because of serious side effects?

Dihydropyrimidine dehydrogenase deficiencies can lead to an intolerance of high doses of 5-fluorouracil because 5-fluorouracil dihydropyrimidine dehydrogenase.

Consider the breakdown of the four compounds below. Which would be expected to generate $\beta$ -alanine?

To determine the role of glutaredoxin in the generation of deoxyribonucleotides by ribonucleotide reductase, which organisms would be the best to study?

The biosynthesis of CTP is allosterically regulated at many steps. Which of the following is a major point of regulation?

How many PRPP are required to synthesize two UMP and two CTP from carbamoyl aspartate?

Tyr122 is important in the mechanism of the E. coli ribonucleotide reductase. The function of this amino acid in the mechanism is to

A mutation in may alter the rate at which UT is converted to CTP.

The biosynthesis of deoxynucleosides is important, yet different organisms require different sets of enzymes to carry it out. If 100 different species were analyzed, which enzyme is most likely to be found in all of them?

Quiz 18: Nucleotide Metabolism

Which answer INCORRECTLY pairs a substrate and subsequent product of dihydropyrimidine dehydrogenase?

To purify glutathione reductase to carry out a kinetics analysis, which organism would be the best source of the enzyme?

Complete the following pathway of the degradation of UMP. UMP →\rightarrow→ Uridine →\rightarrow→ __________ →\rightarrow→ Dihydrouracil →\rightarrow→ NH4+ + HCO3- + β\betaβ -alanine

Consider a cell that is provided aspartate in which all carbons are radioactively labeled. Compounds in the cell are analyzed after the biosynthesis and subsequent breakdown of pyrimidines. Which of the following compounds would display no radioactivity signal during the analysis?

CTP synthetase is inhibited by __________ and activated by _.

The chemotherapy agent 5-fluorouracil is usually degraded by which of the following enzymes, which requires administration of higher doses?

β\betaβ -aminoisobutyrate is a breakdown product of

How many ATP are converted to ADP during the biosynthesis of CTP from UMP?

What is the name of the compound below, which is an intermediate in the breakdown of some pyrimidines?

Dihydropyrimidine dehydrogenase deficiencies exist in approximately of humans and can result in complications when 5-fluorouracil is administered as a therapy.

An oncologist has a patient with dihydropyrimidine dehydrogenase deficiency. Which of the following is a chemotherapy agent that the doctor should be cautious about using with this patient because of serious side effects?

Dihydropyrimidine dehydrogenase deficiencies can lead to an intolerance of high doses of 5-fluorouracil because 5-fluorouracil dihydropyrimidine dehydrogenase.

Consider the breakdown of the four compounds below. Which would be expected to generate β\betaβ -alanine?

To determine the role of glutaredoxin in the generation of deoxyribonucleotides by ribonucleotide reductase, which organisms would be the best to study?

The biosynthesis of CTP is allosterically regulated at many steps. Which of the following is a major point of regulation?

How many PRPP are required to synthesize two UMP and two CTP from carbamoyl aspartate?

Tyr122 is important in the mechanism of the E. coli ribonucleotide reductase. The function of this amino acid in the mechanism is to

A mutation in may alter the rate at which UT is converted to CTP.

The biosynthesis of deoxynucleosides is important, yet different organisms require different sets of enzymes to carry it out. If 100 different species were analyzed, which enzyme is most likely to be found in all of them?

$\beta$ -aminoisobutyrate is a breakdown product of

Consider the breakdown of the four compounds below. Which would be expected to generate $\beta$ -alanine?