Protein structure is key in protein function:
Amino acids consist of an amine group, a carboxylic acid group, Primary structure – Two amino acids join in a condensation reaction to form a dipeptide (this can be more than two amino acids in length and they are joined by a peptide bond) Secondary structure – The chain of amino acids twist to form an alpha-helix, hydrogen bonds form
between the C=O of the carboxylic acid and the -NH of the amine group of different amino acids. Several chains my link together forming a beta-pleated sheet.
Tertiary and quaternary structure – a polypeptide chain bends and folds to produce a threedimensional shape (maintained by interactions between R groups) A protein may be made up of several polypeptide chains held together this is known as the quaternary structure.
Proteins are divided into two groups:
• globular proteins
• fibrous proteins
• folded into a compact spherical shape
• soluble because of hydrophilic side chains that are on the outside of them
• enzymes are globular proteins
• their three-dimensional shape is critical to their roles in binding to other substances
• e.g. of a globular protein is transport proteins within membranes
• are long chains
• several polypeptide chains can be cross linked for additional strength
• they are insoluble
• e.g. of a fibrous protein is keratin found in the hair and skin