Question

Resistance to methotrexate, which inhibits the enzyme dihydrofolate reductase (DHFR) is used as a selectable marker. This enzyme is involved in the synthesis of _____ carbon units and is required for _____ biosynthesis.

(a) two, nucleoside

(b) two, nucleotide

(c) one, nucleotide

(d) one, nucleoside

I had been asked this question by my school principal while I was bunking the class.

The query is from Cultured Cells in Mammals and Restricted Areas in Intact Organisms topic in portion Using Other Organisms of Genetic Engineering

Answer 1

Right option is (d) one, nucleoside

Easy explanation: Resistance to methotrexate, which is used as a selectable marker inhibits DHFR enzyme. This enzyme is involved in the synthesis of one carbon units and is required for nucleoside synthesis.