Proteins

amino acid

monomers that link together to form polypeptides and proteins, they contain an amino group (NH₂), a carboxyl group (COOH), a hydrogen atom, and a variable R group

dipeptide

a molecule of 2 amino acids joined together by a peptide bond

polypeptide

a chain of amino acids joined by peptide bonds

R - group

variable part of amino acid that differs one amino acid to another

Amine group

functional group for all amino acids, (NH₂)

peptide bond

a covalent bond between the carboxyl group of one amino acid and the amino group of another

hydrogen bonds

hydrogen bond forms between hydrogen atom and an oxygen or nitrogen atom, helping to maintain the shape of proteins and DNA

ionic bonds

formed by attraction between oppositely charged ions. In proteins, ionic bonds form between positively and negatively charged R groups

disulfide bridge

strong covalent bond between two cysteine amino acids, helping to stabilise a proteins 3D structure

cysteine

amino acid that contains a sulfur containing R group

alpha helix

arrangement of polypeptide chain stabilised by hydrogen bonds between the peptide backbone

beta pleated sheet

formed by folded polypetide chains, important in secondary structure of proteins

enzyme

a biological catalyst which speeds up a chemical reaction without being used up

antibodies

proteins produced by the immune system that recognise and bind to specific antigen and helps the body to defend against infection

Transport proteins

proteins that carry specific molecules or ions across a membrane

structural proteins

protein that forms physical structures and helps maintain the shape and strength of tissues

biuret test

chemical test to detect proteins, solution changes from blue to lilac

Primary structure

specific sequence of amino acids in a polypeptide chain.

Secondary structure

secondary structure of a protein is the local folding of the polypeptide chain into an alpha helix or beta pleated sheet, stabilised by hydrogen bonds between the peptide backbone.

Tertiary structure

the three-dimensional shape formed when a polypeptide folds due to interactions between the R groups of its amino acids.

Quaternary structure

quaternary structure of a protein is formed when two or more polypeptide chains associate and are held together to make a functional protein.