Deck 19: Nucleotide Metabolism

Question 1

Which statement about nucleotides is FALSE?

A) Most cells contain 5 to 10 times more RNA than DNA.
B) Ribonucleotides have a number of different metabolic roles.
C) The only role of deoxyribonucleotides is as constituents of DNA.
D) The electrons for reduction of ribonucleotides to the corresponding deoxyribonucleotides ultimately come from NADPH.
E) dTTP can only be synthesized from dCDP.

Answer 1

E

Question 2

The end product of purine catabolism in humans is:

A) xanthine.
B) uric acid.
C) allantoin.
D) urea.
E) hypoxanthine.

Answer 2

B

Question 3

Inosine 5'-monophosphate, which contains the base hypoxanthine, is a common intermediate for ________ nucleotide biosynthesis.

Answer 3

purine

Question 4

Which of the following enzymes is NOT primarily used in salvage of nucleic acids because the pyrophosphate product is rapidly hydrolyzed?

A) Endonuclease
B) Phosphodiesterase
C) Nucleotidase
D) Phosphoribosyltransferase
E) None of the above

Question 5

5-phosphoribosyl-α-D-1-pyrophosphate is a key intermediate in de novo synthesis of nucleotides but not in salvage pathways.

Question 6

While purines are assembled as nucleotides early in their biosynthetic pathway, the pyrimidine ring is assembled as a ________.

Question 7

The mechanism of action of dihydrofolate reductase inhibitors used for chemotherapy is based on their ability to block the synthesis of dTMP.

Question 8

Glutamine amidotransferases require ATP hydrolysis to make the ________ of glutamine biosynthetically active.

Question 9

5-fluorouracil and 5-fluorodeoxyuridine are both prodrugs and potent inhibitors of DNA synthesis because they can be converted in the cell to 5-fluorodeoxyuridine monophosphate, an irreversible inhibitor of ________.

Question 10

All six atoms in the pyrimidine ring are derived from two amino acids.

Question 11

Formyltransferases, which are ________ dependent, are involved in several steps of purine nucleotide biosynthesis.

Question 12

Nucleoside phosphorylase cleaves a glycosidic bond to yield a base and either ribose-1-phosphate or deoxyribose-1-phosphate.

Question 13

The initial end products of purine nucleotide biosynthesis are monophosphates.

Question 14

Humans and great apes do not make the enzyme urate oxidase and are hence prone to gout from the crystallization of ________ in synovial fluid of joints.

Question 15

Which of the following compounds is NOT a precursor for nucleotide biosynthesis?

A) Aspartate
B) Glutamine
C) Glycine
D) Fumarate
E) Carbamoyl phosphate

Question 16

Ganciclovir or Acyclovir can be used treat herpes virus infections because they are nucleoside analogues that become phosphorylated by the viral thymidine kinase and interfere with viral ________.

Question 17

Which of the following statements about purine biosynthesis in vertebrates is FALSE?

A) Many of the proteins are multifunctional in that they have more than one active site.
B) Six proteins form a multienzyme complex with covalent linkages.
C) The multienzyme complex is called a purinosome.
D) Two enzymes of single carbon metabolism are associated with the multifunctional enzyme complex.
E) One of the enzymes that contributes to the formation of 10-formyl-tetrahydrofolate is a multifunctional enzyme.

Question 18

All of the dNTPs are produced in approximately the same amounts because the first step in each pathway is catalyzed by the same ribonucleotide reductase enzyme.