Enzymes are proteins that act as organic catalysts to speed chemical reactions within cells. Insulin protein is a hormone that regulates glucose content of blood. Hemoglobin transports oxygen in blood. Proteins embedded in the plasma membrane have varied enzymatic and transport functions. Polarity of the peptide bond permits hydrogen bonding between parts of a polypeptide.
Amino acids differ in nature of R group, ranging from single hydrogen to complicated ring compounds.
There are 20 different amino acids commonly found in cells. A peptide is two or more amino acids joined together. Polypeptides are chains of many amino acids joined by peptide bonds. Both temperature and pH can change polypeptide shape. When such proteins lose their normal configuration, the protein is denatured.