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. For an amino acid with only one amine and one carboxyl group, the pI can be calculated from the mean of the pKas of this molecule.
Khan Academy provides short tutorial about amino acids and proteins HERE.
Useful outline can be found HERE, too.
A handy tutorial about amino acids
The same thing about proteins
Below you will find some useful pictures of pKa of amino acids at different pH.
Big thanks to http://web.campbell.edu/faculty/chazotte/Courses/PHARM_304/Materials_304/Aminoacids_Proteins.htm and http://www.elcamino.edu/faculty/pdoucette/Calculating-approximate-isoelectric-points.pdf