Question

A student is working in a research lab studying the glucose transporter and evolution of this trans-membrane protein. There is genetic evidence that this transporter may be present in ancient bacteria but so far no functional data. The student designs an experiment where the cells are grown in a monolayer on a semi-permeable membrane on O-rings then placed in a chamber where 13C glucose flux (rate of transport/unit area) is monitored. Experiment is setup to monitor flux of glucose into cells. From data of flux versus glucose concentration, how can the student tell if the process is mediated or non- mediated transport? (Hint competitive inhibitors and chemicals to inactive the transporter are available)

Answer 1

We can use inhibitors to distinguish whether the import of glucose into the vesicles is due to passive diffusion or by carrier-mediated transport.

If glucose import into the vesicles is by simple passive diffusion, there will not be any difference in the amount of imported glucose into vesicle in the presence or absence of inhibits of the carrier proteins.

If glucose import into the vesicles is carrier-mediated, there will a difference in the amount of imported glucose into vesicles in the presence and absence of inhibits of the carrier proteins. In the presence of an inhibitor, we would observe less import of glucose into vesicles.