I agree with the above poster. You don't really need to have taken Molecular Cell/Biochemistry to do well on the MCAT. Prep books, for the most part, will teach you pretty much everything you need to know. There really isn't as much actual "biochem" on the new MCAT as people think there is. I will say though that if you were to enroll in the course that you mentioned, it really couldn't hurt you in any way unless you do absolutely terrible in it. If anything, it'll just prepare you better for when you see the same subject material in med school. You probably won't remember much by the time you start school, but maybe bits and pieces will slowly come back to you as you are deep in your studies.