All proteins are made up of amino acids. There are 20 different kinds of amino acids. These amino acids, in various combinations form long strings to form the base or the primary sequence of the protein. These amino acids have charged, hydrophobic (greasy) or polar (water friendly) side chains which contribute to its folding.
These sequences fold to form secondary structures. Secondary structures like alpha helices and beta sheets are common. These common folds occur due to a combination of hydrogen bonds, stacking interactions, covalent bonds such as cysteine disulphide bonds and van der waals interactions, determined by the side chains of amino acids.
These secondary structures fold into a more global tertiary structure, which can be the final structure of the protein.
If the protein is multimeric or has multiple subunits then one or more protein monomers come together to form a quaternary structure! In multimeric proteins, all of the individual subunits can work together or in tandem to function optimally!
