1. a-keratin is the structural protein of hair, horns and nails

2. Actin and myosin are the contractile proteins of muscle
Tubulin is the protein of the microtubules; eukaryotic cilia and mitotic spindles are composed of microtubules

3. Thrombin and fibrin are blood clotting proteins
Thrombin is an enzyme that catalyses the conversion of the soluble blood protein fibrinogen into fibrin
Fibrin forms the fibres that trap red blood cells to form a clot

4. Antibodies (immunoglobulins) are the proteins of the immune system; antibodies are manufactured by the B-lymphocytes and interact with specific, foreign antigens that gain entry to the body

5. These mussels secrete specialised glue proteins to attach themselves to the rocks

6. Proteins made from monomers called amino acids
All amino acid possess amino and carboxylic acid ends
There are 20 different naturally occurring amino acids
Amino acids differ by in the nature of their R groups
Amino acids bond together forming peptide bonds
When two amino acids bond during a condensation reaction, the resulting molecule is a dipeptide
When many amino acids bond together, the resulting molecule is referred to as a polypeptide

7. Chains of amino acids numbering greater than 100 are generally referred to as proteins
Individual amino acids may be neutral, basic or acidic
Two amino acids, namely cysteine and methionine, possess sulphur atoms in their R groups
The type, number and sequence of amino acids forming the original linear chain of a protein is termed the primary structure of a protein
Different proteins have different primary structures
The primary structure determines the final shape of the protein molecule

8. The linear chain of amino acids making up the primary structure of the protein bends and folds in various ways to form the secondary structure of the protein
Two main types of secondary structure are found in proteins - the beta pleated sheet and the alpha helix
The alpha helix forms when the linear chain coils into a right handed helix
The beta pleated sheet forms when the linear chain folds back on itself many times
Hydrogen bonds play a major part in stabilising the secondary structure of proteins
Many proteins bend and fold further to form globular tertiary structures

9. Myoglobin is a globular protein displaying the tertiary level of structure
Myoglobin is a protein found in muscle cells
Proteins consisting of more than one polypeptide chain display quaternary structure
Haemoglobin is a protein consisting of more than one polypeptide chain
Haemoglobin consists of four separate polypeptide chains held together by weak van der Waals forces
Each polypeptide chain in haemoglobin contains a haem group that binds to molecular oxygen
The role of haemoglobin is to transport oxygen molecules from the lungs to the body tissues

10. A variety of different bonds stabilise the secondary and tertiary structures of proteins
Hydrogen bonds form between oxygen and hydrogen atoms within the main amino acid chain and between the R groups
Disulphide bridges form between sulphur atoms in the R groups of amino acids such as cytseine
Ionic bonds form between charged amino groups and charged carboxylic acid groups
Hydrophobic interactions occur between R groups that have clustered towards the centre of protein molecules due to their hydrophobic nature
The Biuret test is used to detect proteins; a positive result gives a violet/lilac colour