There are 21 common amino acids, and one that is less common. The enormous diversity of the chemical side chain allows an organism to make many different knids of proteins with various biochemical properties. Four amino acids are polar e.g. glutamate, aspartate, lysine, arginine, with the rest being hydrophobic, e.g. leucine, valine etc. Enzymes serve as catalysts for a variety of chemical reactions within the cell, whereas structural proteins help maintain the structural integrity of the cell. The linear array of amino acids is called the p rimary structure and specifies which amino acids are in the polypeptide chain.
Proteins are molecules that fold and twist into many physical conformations.
Each conformation is dictated by the nature of the chemical side chains. The secondary structure is held together by hydrogen bonds between the carboxyl and amino groups that have formed a peptide bond. Tertiary protein structure occurs when a given secondary structure domains interact through folding and twisting of the polypeptide chain. This produces an even more stable protein molecule. Formation of disulphide bonds is very important in maintaining tertiary structure.