[The weigh of GPA on PhD program admission]

Hi y'all,

I'm currently a sophomore chemistry student struggling through finals at UT at Austin. I really want to go to graduate school for organic chemistry and this semester has been horrible for me in term of grades.

I'm aiming to get As for my chemistry courses. Currently, my GPA for chemistry is 3.9 and my cumulative GPA is around 3.66. However, by the end of this semester, my cumulative GPA will go down to 3.56. I have been researching since the Spring of freshman year and will be joining and continuing so with an amazing research group. I only have been presenting at my school forum but planning to attend and present as much as conferences as I can. 

I really want to aim to apply good top 15 graduate organic chemistry programs such as UMich, U Wishconsin, Princeton, etc. So my question is how important is GPA to get into these programs? Do i need to keep at least above 3.5? Or my chances are gone? 

Thank you so much!