I have to agree that every C is a POTENTIAL "nail in the coffin" but don't let it scare you off if you happen to get a few!
I made C's in Organic yet I've already gone to 2 interviews and have 2 more scheduled (and haven't heard from my last 3 schools).
The point is that you DON'T want to get them if you can help it, but if you do, try to take other, similar courses (ie: biochem,etc) to prove that you CAN handle the load! Keep trying and you'll get there!
Good Luck!