For the hardest part in biology olympiads has always been biochemistry. Thus, I would like you to be the best in this field, so here you will find some good notes of amino acids and proteins from the biochemical point of view.
Especially pay your attention to isoelectric point and pK calculations. The isoelectric point, sometimes abbreviated to IEP, is the pH at which a particular molecule or surface carries no net electrical charge.
Khan Academy provides short tutorial about amino acids and proteins HERE.
Useful outline can be found HERE, too.
http://web.campbell.edu/faculty/chazotte/Courses/PHARM_304/Materials_304/Aminoacids_Proteins.htm
http://www.elcamino.edu/faculty/pdoucette/Calculating-approximate-isoelectric-points.pdf
