What is a protein? How are proteins made?

Proteins, also known as polypeptides, are amino acid sequences. All proteins are made of amino acids.Proteins exhibit variance. This is due to the fact that there can be a myriad of possible combinations: there are only 20 amino acids, but most polypeptides are composed of thousands and thousands of amino acids!Polypeptides are formed on ribosomes (which are respectively made of (A) ribosomal RNA and (B) protein, for structural support).Amino acids are linked via peptide bonds. A peptide bond occurs between the carboxyl group of an amino acid (-COOH) and the amino group of another (-NH3). It is a condensation reaction, and thus yields water.When broken down (e.g. by protease enzymes), a reverse reaction occurs: hydrolysis. The peptide bond is broken, and water is taken up to restore the normal structure of an amino acid (regenerating the -COOH and the -NH3 ends).