What was the purpose of adding methotrexate to the cells expressing a genetically-engineered Dihydrofolate Reductase enzyme in the mitochondrion-targeting experiment we discussed in lecture?

Methotrexate inhibits the synthesis of DNA, RNA, and protein synthesis of the cells in the experiment.

Explanation:

Methotrexate competitively inhibits the enzyme dihydrofolate reductase (DHFR) which is involved in the synthesis of tetrahydrofolate from the inactive dihydrofolate. The methotrexate blocks the enzyme by binding to its active site thereby preventing further reaction of the dihydrofolate reductase enzyme and dihydrofolate. Tetrahydrofolate is a useful material for the de novo synthesis of thymidine, a nucleoside. And without thymidine, DNA synthesis is hindered. Methotrexate therefore inhibits the synthesis of DNA, RNA, thymidylates and of course protein synthesis.

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