I would talk to the Professor and see what resources are available to help you (there will be some). Make use of those resources! This will probably mean a few extra hours a week working on stuff.
The other thing is that in Yeshiva you probably got pretty good at memorizing stuff, this is a useful skill in bio and chem class.
Oh and remember to have fun! This stuff when taught well is very interesting. My father is a biologist so I grew up around science.
There is a saying I like:
It will be difficult at first, but everything is difficult at first