Protein Structure

Transcription

Translation

Epigenetics

Transcription

Translation

Mutation

B1.2.7
Impact of primary structure on the conformation of proteins

Primary Structure (1º)

The first level of structural organisation in a protein is the order / sequence of amino acids which comprise the polypeptide chain
The primary structure is formed by covalent peptide bonds between the amine and carboxyl groups of adjacent amino acids
Primary structure controls all subsequent levels of organisation because it determines the nature of the interactions between R groups of different amino acids

B1.2.8
Pleating and coiling of secondary structure of proteins

Secondary Structure (2º)

The secondary structure is the way a polypeptide folds in a repeating arrangement to form α-helices and β-pleated sheets
This folding is a result of hydrogen bonding between the amine and carboxyl groups of non-adjacent amino acids
Sequences that do not form either an alpha helix or beta-pleated sheet will exist as a random coil
Secondary structure provides the polypeptide chain with a level of mechanical stability (due to the presence of hydrogen bonds)
In pictures, alpha helices are represented as spirals (purple ; left) and beta-pleated sheets as arrows (blue ; right)

B1.2.9
Dependence of tertiary structure on hydrogen bonds, ionic bonds, disulfide covalent bonds and hydrophobic interactions

Tertiary Structure (3º)

The tertiary structure is the way the polypeptide chain coils and turns to form a complex molecular shape (i.e. the 3D shape)
It is caused by interactions between R groups; including H-bonds, disulfide bridges, ionic bonds and hydrophobic interactions
Relative amino acid positions are important (e.g. non-polar amino acids usually avoid exposure to aqueous solutions)
Tertiary structure may be important for the function of the protein (e.g. specificity of active site in enzymes)

B1.2.11
Quaternary structure of non-conjugated and conjugated proteins

Quaternary Structure (4º)

Quaternary structures are found in proteins that consist of more than one polypeptide chain linked together
- Insulin (two chains) and collagen (three chains) are examples of proteins with a quaternary structure
Alternatively, proteins may have a quaternary structure if they include inorganic prosthetic groups within their structure (conjugated protein)
- Haemoglobin is a conjugated protein as each subunit associates with an iron-containing haeme group
Not all proteins will have a quaternary structure – many proteins will only consist of a single polypeptide chain

Protein Structure Overview