Question 12 of 16

The answer you chose is highlighted in reverse video. The correct answer is in bold.

Methotrexate is an inhibitor of dihydrofolate reductase. Administration of methotrexate would inhibit:

1. de novo synthesis of UMP.

2. conversion of dUMP to dTMP.

3. conversion of IMP to GMP.

4. de novo synthesis of IMP.

A. 1, 2 and 3

B. 1 and 3

C. 2 and 4

D. 4 only

E. All four

The correct answer is (C).

Comments:

1. Pyrimidine synthesis doesn't involve the one-carbon pool.

2. The methyl group that appears in dTMP is synthesized during the transfer of the methylene group from the one-carbon pool.

3. This conversion involves an oxidation and an amination but no additional carbons.

4. Purine synthesis requires two components of the one-carbon pool. In the absence of this enzyme, dietary folate could not be reduced to the tetrahydro form necessary for carbon carriage.

Return to Question Document

cna

Last modified 1/5/95