Protein Structures

Proteins are made up of monomers called amino acids, which are organized into polypeptide chains. When a polypeptide chain is very long, it is called a protein. Proteins have 4 structures to them. The primary strucutre is the sequence of amino acids. This sequence has directionality, which is determined by the free amino group at the start, and the free carboxyl group at the end. The primary structure of a protein is linked by covalent peptide bonds, formed through dehydration reactions between indavidual amino acids.

The secondary strucutre of protein is made of alpha-helicies and beta-sheets. Each of these is stabilized by hydrogen bonds between the atoms of the backbone of the peptide chain, with no interaction between R-groups. The R-groups will however fan out of an alpha-helix and point above and below a beta-sheet.

Tertiary stucture is the folded shape of a single protein subunit. This structure is stabilized by all noncovalent bonds and disulfide bonds. The tertiary strucutre is also where R-groups will interact. The hydrophillic and hydrophobic effect acts heavily here as the protein will fold to create a hydrophobic core, leaving its surface hydrophillic. That is because in a cell, the environment is mostly aqueous, thus the increase entropy hydrophobic regions will aggragate together. Tertiary structure is very similar to quaternary structure, with the exception that quaternary includes all subunits of a protein, from multiple polypeptide chains and domains.