Some are structural, some are enzymes, some penetrate cell membranes. Their primary structure is the a.a. sequence, secondary is either a spiral or sheet arrngement, tertiary is the folding of the chain and quartenary is the combination of several polypeptide chains into a complex protein. They produce about 4.5 Kcal per gram. They contain amine groups. While water molecules have no net charge, the charge is distributed asymmetrically over the molecule making it polar.
Science is a body of knowledge based on controlled experiments.