proteins

Proteins

polymers made up of monomers called amino acids

The general structure of all amino acids

a central carbon atom bonded to an anime group (NH2), a carboxylic acid group (COOH), a hydrogen atom and an R group

R group

affects the way amino acids interact with others within the protein molecile

Bonds which link amino acids to each other to form protein

Peptide bonds

Primary structure of protein

the sequence of amino acids in a polypeptide chain held together by a peptide bond

Secondary structure of protein

the folding of the polypeptide chain into a regular repeating 3D structure. the two secondary structures are alpha helix and beta pleated sheets

Alpha helix

the polypeptide chain is wound to form a helix and is held together by hydrogen bonds running parallel with the long helical axis. there are many hydrogen bonds making this a very stable structure

Beta pleated sheets

the polypeptide chains zig zags back and forth forming a sheet held together by hydrogen bonds running

Tertiary structure of protein

the complex 3d globular shape the polypeptide chain takes when the polypeptide chain twists and folds around itself

Tertiary structure is maintained by

Hydrogen bonds, ionic bonds, disulfide bonds, hydrophobic and hydrophilic interactions

Hydrogen bonds in tertiary structure of protein

formed between some H and O atoms. when these charged groups are close to each other, opposite charges attract forming hydrogen bond.
although these bonds are weak, the large number of bonds provide a considerable force to maintain the 3D shape

Ionic bonds in tertiary structure of protein

formed between some of the strongly positive and negative amino acid chains which are found deep inside the protein molecule. they are stronger than hydrogen bonds, but can be broken by changes in pH and high temperature

Disulfide bonds in tertiary structure of protein

formed between two sulphur atoms close together. an oxidation reaction occurs between the two sulphur containing groups resulting in a strong covalent bond known as a disulphide bond.
these disulphide bonds are much stronger than hydrogen bonds but they appear less often.
they are important for holding the folded polypeptide chains in place

Hydrophobic and hydrophilic interactions in tertiary structure of protein

the hydrophobic regions of the polypeptide chain face away from water by folding inwards
the hydrophilic regions of the polypeptide chain remain on the surface of the globular structure

Quaternary structure of protein

the linking together of two or more polypeptide chains and describes the way these polypeptide chains fit together in three dimensions