not to sound snobby, but if the requirements on some of the school's websites say a committee letter or 2 science letters and a DPM letter, don't you think you need one more science letter.
And by science I'm pretty sure it includes all sciences - when I applied last year I got one from my statistics professor because it fell in the math and stat dept.
This is just my 2 cents. you might be able to get away with what you currently have but if you want to make sure the best thing to do is call the schools personally. Good luck - I know finding a professor to write is sometimes difficult!