AS AQA Biology: Biochemistry: Proteins

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Largest and most diverse group, many functions:

Structure Enzymes Transport Pumps Motors Hormones Receptors Antibodies

Storage Blood Clotting Lubrication Toxins Antifreeze and more!

Proteins are made of amino acids, made up of Carbon, Oxygen, Hydrogen, Nitrogen and Sulphur. A key for the general structure is below:

H2N: Amino group (base)

H: a Carbon

COOH: Carboxylic acid group (acidic)

R: Variable group

(I'd reccomend sticking a picture of it here, it won't let me copy the pictures I put in my originals).

Opposite chains, acid and base, have opposite charges. The charge changes with PH change; this explains the effect PH has on enzymes as they are proteins.

There are twenty different R groups and so twenty different amino acids each with different properties.


Amino acids are joined together with peptide bonds; this is a condensation reaction, so water is formed from it. The new molecule formed from two is known as a dipeptide, three it is a tripeptide and then polypeptide for more than three. In a polypeptide there is always a free amino group and a free carboxyl group.

Structure of Proteins


Sequence of amino acids in the polypeptide chain.


Basic protein folding

The secondary structure is held together


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