The structural tissues of the body, along with enzymes and hormones are composed of a type of macromolecule known as a protein.
Macromolecules are formed when small organic sub-units join to form larger molecules and in the case of proteins, those smaller molecules are called amino acids. The amino acids are referred to as monomers and when many monomers join together chemically, they form a protein which is a polymer. To link two amino acids together, a covalent bond called a peptide bond forms between the amino group of one amino acid and the carboxyl group of the next amino acid in the polypeptide chain. Eventually, this polypeptide will fold into a functional three-dimensional shape and will become a protein.
Proteins make up approximately half of the mass of cells, excluding water. They are components of cell membranes, provide structural support, help facilitate chemical reactions in their role as enzymes, help with cellular communication, provide movement as is seen in the action of muscle cells and they help with the immune response.
There are thousands of different proteins in the body which have unique three dimensional shapes. There are twenty amino acids which are arranged differently to form various proteins, according to the genetic code.
There are numerous proteins in the body, with diverse structures that carry out many different functions necessary for survival.
I have included a link which shows how two amino acids form a peptide bond.