OP, biochem and organic chemistry should actually supplement your MCAT studying. I took those same classes the same semester I took the MCAT and thought that the classes helped a lot with the chemistry portions of the MCAT (orgo and gen.). The opposite holds true as well. I did well on biochem because I knew a lot of o-chem and gen. chem.
My advice to you is to make sure that when you're learning the concepts in class, realize that it's also going to be some of the same stuff for the MCAT. Also, take a break every once in a while! It's a mental marathon, so make sure you get plenty of rest (both mental rest and physical rest). Remember that this test has an ENORMOUS influence on where you end up next year. I had that thought in the back of my mind as motivation to study; however, there were times where I was just plain exhausted. For me, the best indicator of how much I've burned out is whether or not I want to study, despite knowing the significance of my MCAT score. I usually just stopped for the day. Good luck OP! If you study hard, you'll do just fine!
P.S. I don't recommend a week-long break unless you really really really really really really really need it. If you end up giving yourself that, it will be tempting to do it again, which is not good. Also... Sleeping a good amount of hours( >8 ) really helps get your mental gears working in the right mindset, from my experience.