The functions of proteins are extremely varied but are all made up of amino acid subunits.

Proteins are polymers made of monomers called amino acids. The chains of amino acids are called polypeptides. The shape of a protein is determined by the specific sequence of amino acids in the chain

Amino acids have the same basic structure. Attached to a central carbon atom are:

An amino group: -NH2, at the end of one molecule.
A carboxyl group, -COOH, at the other end of the molecule.
A hydrogen atom.
The R group, different in each amino acid.

- At pH7 (pH of a cell), it gains a H and becomes positively charged.

- The carboxyl group is acidic and at this pH it loses a H, becoming negatively charged

- So at pH7, an amino acid has a both positive and negative charge.

Formation of a peptide bond:

The amino group of one amino acid reacts with the carboxyl group of another with the elimination of water. The bond formed from this condensation reaction is a peptide bond, and the resulting compound is a dipeptide.

Protein Structure:

The shape of the protein is held together by H bonds between some of the R groups and ionic bonds between positively and negatively charged side chains.

The protein may be reinforced by strong covalent bonds called disulphide bridges which form between two amino acids with sulphur groups on their side chains.

Primary structure:

The order of amino acids in a polypeptide chain (up to 20 amino acids).
The primary structure is determined by the base sequence on one strand of DNA molecule.

Secondary structure:

The shape polypeptide chains form as a result of hydrogen bonding between the =O on -CO groups, and the -H on -NH groups in the peptide bonds along the chain.
Causes the long polypeptide chain to be twisted into a 3D shape.
The spiral shape is the a-helix. Another arrangement is the B-pleated sheet.

Tertiary structure:

The tertiary structure of proteins is their 3D shape which is highly folded and has a unique structure and this structure gives proteins their specific function. The shape is maintained by:

Hydrogen bonds
Ionic bonds
Disulphide bonds
Hydrophobic interactions

These bonds are important in giving globular proteins, e.g. enzymes, their shape. For example, if insulin was misfolded, it would cease to function properly.

This unique structure gives proteins their specific function. For example, if insulin was misfolded, it would cease to function properly. The origin of misfolding is likely to be in the primary structure, due to a mutation.

If the gene responsible for coding the amino acid sequence for insulin was mutated, then the insulin's primary structure would be different, leading to a different secondary & tertiary structure, and ultimately, a lack of proper function.

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