Hi Twinkies.
I got a D in biochem during my 3rd year of college, but I retook it in my 4th year and got an A. The D was mostly due to difficult circumstances, and I explained that in both my personal statement and my interviews. So far, I've received one acceptance - from the Medical College of Ohio. So in the end, it is possible to still be accepted into med school, but it can complicate things. I would suggest that you do your best to make sure your grades show an upward trend (as you mentioned) and to reflect on why you were struggling and what you needed to do to improve. That way you can both avoid similar struggles in the future and have some kind of explanation ready for any Admissions Committees that are wondering about your poorer grades. Good luck!