Which structure of protein is controlled by genes?

Which bond connects two amino acids?

Which bonds are present in the formation of quaternary protein structure?

Which of the following proteins is the most abundant in animals?

Given below are two statements:
Statement $I:$ Amino acids have a property of ionizable nature of $-NH_2$ and $-COOH$ groups,hence have different structures at different $pH$.
Statement $II:$ Amino acids can exist as Zwitterionic form at acidic and basic $pH$.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which one of the following is an alcoholic amino acid pair?