o chem 2 is probably not terribly important, but biochemistry is a MUST. Biochemistry concepts permeate both BB & CP sections.
If you think you can effectively study biochemistry on your own, then yeah, you don't need to wait to take the class to take the MCAT. But that type of self study (not just review, but teaching yourself brand new concepts) takes a lot of dedication and is not for everyone, so make sure that is something you are personally capable of. I learned the hard way that that isn't for me. Just because your peers did it doesn't mean it's a good idea for you, and that doesn't make you any less capable of being a good doctor than them either. Since I don't know you I can't advise you one way or the other, so be honest with yourself.
Also, if I were to do this, I wouldn't just simply study a review book and call it good. Study a review book, use Khan Academy videos, and find a cheap biochem textbook or two to look up concepts you still have trouble with after the first two steps (review book +khan).
Make sure you can "check off" all the MCAT biochem concepts that the AAMC lists on their website, and do some research on which prep materials are best for biochemistry.
Just to reiterate, biochemistry is the most important subject to have a strong foundation in before taking the mcat.
good luck!