Describe the structure of a protein.

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Proteins are made up of long chains of amino acids (polypeptides) joined together by condensation reaction.

Primary structure

The proteins primary structure is the sequence and order of amino acids in the peptide chain. This is often where mutations occur (within the base sequence of DNA, thus changing the amino acids coded for) altering the whole protein.

Secondary structure

The secondary structure is the shape of the polypeptide chain. Often, either alpha helices, or beta pleated sheaths are formed. The secondary structure also includes hydrogen bonds formed between the oxygen and hydrogens in the peptide chain.

Tertiary structure

The tertiary structure is the 3D shape of the protein - it can either be fibrous or globular. Many polypeptide chains are held together by weak hydrogen bonds. There are so many of these that they add up to create a stable molecule. Proteins involving amino acids with sulfur form disulphide bridges between peptides. these disulphide bridges are very strong.

Fibrous proteins are things like collagen and keratin, and are usually either structural or storage proteins. An example of a globular protein with an alpha helix structure would be haemoglobin - a protein used in the blood to carry oxygen.

Quaternary Structure

This is the arrangement of multiple polypeptide chains within a protein. The interactions holding the chains together are the same as those in the tertiary structure, however are between amino acids in different chains. 

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