You could add up your...grade points x credit hours...from each of your math, physics, chemistry, biology, biochem, and other science classes (I think I covered 'em all), then divide 'em by your total credit hours in said classes.
I'm assuming by BUCM you meant BCPM (your science GPA)?
For example...you have an A- in Genetics Lecture (3 credit hours)
3.67 x 3 = 11 and so on and so forth for each class
Let's say you have a total of 75. Those class are worth 25 credit hours.
Just put what you think it is. If it's wrong (I'm talking like you put physiology in physics and it's actually considered bio, not calculus as foreign language) they'll change it before certifying your application.