Question 1

Which of the following is a true statement regarding pyrimidine biosynthesis in animals?

Accepted Answer

The answer of Which of the following is a true...

Question 2

Which of the following statements regarding the activity of ribonucleotide reductase is correct?

Accepted Answer

The answer of Which of the following statements regarding the...

Question 3

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

Accepted Answer

5-fluorouracil is a suicide substrate for thymidylate synthase, meaning that it incorporates into DNA as a false nucleotide, leading to DNA damage and ultimately cell death.

Question 4

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

Accepted Answer

N¹⁰-formyl THF is directly involved in the synthesis of the purine ring by donating formyl groups required for the formation of purine bases.

Question 5

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

Accepted Answer

Thymidylate synthase synthesizes dTMP from dUMP by methylating it with a methyl group derived from the coenzyme tetrahydrofolate (THF). THF is a carrier of one-carbon units and is involved in the synthesis of nucleotides and amino acids. Choice A is incorrect because dCTP is not a substrate for thymidylate synthase and biotin is not a coenzyme involved in the reaction. Choice C is incorrect because dCMP is not a substrate for thymidylate synthase. Choice D is incorrect because thymidylate synthase does not phosphorylate nucleotides and ATP is not a coenzyme involved in the reaction. Choice E is incorrect because thymidylate synthase does not phosphorylate nucleotides and ATP is not a coenzyme involved in the reaction.

Question 6

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

Accepted Answer

IMP can be converted into GMP through the IMP dehydrogenase (IMPDH) pathway. High levels of AMP can activate AMP-activated protein kinase (AMPK) which, in turn, phosphorylates and activates IMPDH, leading to an increase in the conversion of IMP to GMP. Therefore, high levels of AMP would cause an increase in the conversion of IMP to GMP.

Question 7

Thymine nucleotides are not synthesized directly by cells but indirectly from other pyrimidine deoxyribonucleotides. All of the following statements regarding thymine nucleotide synthesis are true EXCEPT:

Accepted Answer

The action of dUTPase prevents dUTP from being incorporated into DNA and promotes the use of dTTP instead. Thymine nucleotides are synthesized indirectly from other pyrimidine deoxyribonucleotides through the methylation of dUMP to form dTMP, which is catalyzed by thymidylate synthase. The methyl donor in this reaction is 5,10-methylene-THF. THF is used as a cofactor in this reaction.

Question 8

Which of the following is an advantage of metabolic channeling?

Accepted Answer

Metabolic channeling prevents the dilution of substrates and accumulation of intermediates by keeping them within a specific pathway, enhancing efficiency and regulation.

Question 9

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

Electronegative fluorine cannot be readily eliminated as F⁺, thus enzyme inhibitors can be fashioned in which F replaces H at positions where catalysis involves H-removal as H⁺. Options A (sodium) and B (potassium) are not electronegative, and option C (deuterium) is a stable isotope of hydrogen and not an electronegative element.

Question 10

How do cells salvage purines?​

Accepted Answer

The answer of How do cells salvage purines?​...

Question 11

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

Accepted Answer

The answer of Explain the regulation of pyrimidine biosynthesis in...

Question 12

The immediate reducing power of ribonucleotide reductase is provided by:

Accepted Answer

Ribonucleotide reductase requires thioredoxin to provide the immediate reducing power for the conversion of ribonucleotides to deoxyribonucleotides.

Question 13

What type of reaction gives UMP from OMP?

Accepted Answer

The conversion of OMP (orotidine 5'-monophosphate) to UMP (uridine 5'-monophosphate) involves the removal of a carboxyl group (-COOH) as carbon dioxide. This process is known as decarboxylation.

Question 14

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

Accepted Answer

In bacteria, the rate-limiting step in pyrimidine biosynthesis is typically the regulation of aspartate transcarbamoylase (ATCase), which catalyzes the second step in de novo pyrimidine biosynthesis. This enzyme is regulated by feedback inhibition by the end-product, CTP.

Question 15

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

Accepted Answer

The answer of Discuss the regulation of the purine biosynthetic...

Question 16

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

Accepted Answer

Epidermal growth factor (EGF) has been shown to activate CPS-II in mammalian cells. Thyrotropin, cortisol, and gonadotropin do not serve as activators of CPS-II.

Question 17

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

Accepted Answer

R2 has a single active site containing two Fe atoms that generate the free radicals required for reduction. The substrate specificity site on the R1 homodimer does not determine if the enzyme is active or inactive, but rather determines the specificity for the substrate. R1 and R2 both participate in the delivery of reducing equivalents. R2 homodimer carries only one regulatory site. The final step of ribonucleotide reduction involves the addition of an H+ instead of a decarboxylation.

Question 18

Which of the following serves as one of the nitrogen sources for the pyrimidine ring?

Accepted Answer

Carbamoyl phosphate serves as one of the nitrogen sources for the pyrimidine ring. Glutamate, asparagine, and glycine are sources of nitrogen for other metabolic pathways, but not for the synthesis of pyrimidine. Therefore, the correct answer is B) carbamoyl phosphate.

Question 19

​How are nucleotides degraded to uric acid?

Accepted Answer

The answer of ​How are nucleotides degraded to uric acid?...

Question 20

Which of the following is a source of 2 carbon atoms of the purine ring system?

Accepted Answer

Glycine contributes a two-carbon fragment (plus a nitrogen atom) to the purine ring, making it a source of 2 carbon atoms in the purine biosynthesis pathway.

Quiz 26: Synthesis and Degradation of Nucleotides

Which of the following is a true statement regarding pyrimidine biosynthesis in animals?

Which of the following statements regarding the activity of ribonucleotide reductase is correct?

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

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

Thymidylate synthase synthesizes dTMP from by utilizing the coenzyme .

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

Thymine nucleotides are not synthesized directly by cells but indirectly from other pyrimidine deoxyribonucleotides. All of the following statements regarding thymine nucleotide synthesis are true EXCEPT:

Which of the following is an advantage of metabolic channeling?

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⁺.

How do cells salvage purines?

Explain the regulation of pyrimidine biosynthesis in bacteria and animals.

The immediate reducing power of ribonucleotide reductase is provided by:

What type of reaction gives UMP from OMP?

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

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

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

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

Which of the following serves as one of the nitrogen sources for the pyrimidine ring?

How are nucleotides degraded to uric acid?

Which of the following is a source of 2 carbon atoms of the purine ring system?

Quiz 26: Synthesis and Degradation of Nucleotides

Which of the following is a true statement regarding pyrimidine biosynthesis in animals?

Which of the following statements regarding the activity of ribonucleotide reductase is correct?

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

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

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

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

Thymine nucleotides are not synthesized directly by cells but indirectly from other pyrimidine deoxyribonucleotides. All of the following statements regarding thymine nucleotide synthesis are true EXCEPT:

Which of the following is an advantage of metabolic channeling?

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+.

How do cells salvage purines?​

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

The immediate reducing power of ribonucleotide reductase is provided by:

What type of reaction gives UMP from OMP?

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

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

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

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

Which of the following serves as one of the nitrogen sources for the pyrimidine ring?

​How are nucleotides degraded to uric acid?

Which of the following is a source of 2 carbon atoms of the purine ring system?

Thymidylate synthase synthesizes dTMP from by utilizing the coenzyme .

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⁺.

How do cells salvage purines?

Explain the regulation of pyrimidine biosynthesis in bacteria and animals.

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

How are nucleotides degraded to uric acid?