proteins

definition of a protein

a polymer built from amino acids joined by peptide bonds

what is a polypeptide

chain of amino acids

two linked amino acids

dipeptide

multiple linked amino acids

polypeptides

definition of endopeptide

breaking down bonds within peptide chain into smaller peptide fragments

definition of exopeptide

breaking down bonds on the ends of chains, releasing just single amino acids

what does the primary structure of a protein consist of?

• number and order of amino acids in a polypeptide

• held together with peptide bonds between adjacent amino acids

what does the secondary structure of proteins consist of?

• segments of the polypeptide chains that are repeatedly coiled/folded into patterns that contribute to the protein’s overall shape

• coils (turn into an alpha helix chain) and folds (beta pleated sheet) are a result of hydrogen bonds between the repeating constituents of the polypeptide backbone, not the amino acid side chains

what does the tertiary structure of a protein consist of?

determined by a number of interactions, initially by hydrophobic interactions and then by hydrogen bonds, ionic bonds and disulphide bridges (which are by far the strongest since they are covalent bonds)

what does the quaternary structure of a protein consist of?

some proteins are made up of multiple polypeptide chains, these proteins have quaternary structure. the interactions involved in stabilising the quaternary structure are the same as those in the tertiary structure

where does the reaction to join amino acids occur and with what?

in the ribosomes and are catalysed by specific enzymes

how do you test for proteins?

using the biuret’s test:

• add an equal volme of NaOH to a solution of the sample

• add a few drops of aqueous copper (II) sulphate

• positive result would show the solution turning mauve/purple

what are the functions for proteins?

structural proteins, contractile proteins, hormones, transport into and out of cells, defence & enzymes

function of structural protein

support

function of transport protein

transporting or carrying other molecules

function of hormone proteins

homeostasis etc.

function of receptor proteins

enable cell responses

function of contractile proteins

movement

function of defensive proteins

immunity

function of enzymes

catalyse reactions