Hello,
Whenever you think about secondary structure you should always associate it with hydrogen bonds. It is the main stabilizer and that is what you should know for the MCAT.
The amino acid group can affect the stability and characteristics of the helix. For example in sickle cell disease, there is a swap of amino acids and it essentially breaks the secondary structure. For other molecules like collagen smaller amino acids make for a tighter helix which helps with stability for this is all just for your interest.
Kennedy