Here is a list of major requirements for Biochem. Your orientation advisor can give you suggestions of which classes you should start taking. Most likely you want to start with the General Chem series 2A and Lab, along with Math 17A and possible 1-2 GE’s in Literature/History/Philosophy etc… Or a Freshman Seminar. You do not want to take more than 15 units Fall quarter to allow yourself time to get use to the pace of the quarter system and get your bearings at a UCD.
http://catalog.ucdavis.edu/programs/MCB/MCBreqt.html
The Freshman orientation is pretty comprehensive so you will get all the information needed. You should take the Math and Chem placement tests prior to orientation since you will not be allowed to sign up for these classes without them.