The enzyme dihydrofolate reductase (DHFR) normally resides in the cytosol, and DHFR can be imported into mitochondria by appending a mitochondrial signal sequence. However, when this modified DHFR is incubated with methotrexate, which is a substrate analog that binds tightly to the active site, the modified DHFR is no longer imported. a) Propose an explanation for why methotrexate prevents import of DHFR into mitochondria. b) Suppose that DHFR were modified instead by appending a nuclear localization signal. Would you expect methotrexate to prevent transport of this modified DHFR into the nucleus? Why or why not?

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Mitochondrial Mutations

A mitochondrion is a cellular organelle that serves as the site for cellular respiration and energy production (ATP or Adenosine Triphosphate). It is a double-membrane-bound organelle and is only present in eukaryotic cells.