Protein Structure

Proteins are large molecules made of amino acids

An amino acid has a central carbon (alpha carbon) C

An amino group is attached to the alpha carbon on the left-hand side H-N      /    H

A carboxyl (acid) group is attached to the alpha carbon on the right-hand side -C=O   \    OH

The alpha carbon also has an 'R' group attached, a group that is different depending on what amino acid it is.

The final bond (C has 4) is to a single hydrogen

Polypeptides are formed in condensation reactions (water is a product) 

Peptide bonds form between the C and N of the relative amino acids.

Amino acids are joined in ribosomes to make proteins; they are then used in the cytoplasm or are transported out of the cell

Proteins are used for: enzymes, muscles (movement), keratin, collagen, antibodies; haemoglobin

Primary protein structure:

- is a sequence of a chain of amino acids

Secondary protein structure:

- occurs when the sequence of amino acids are linked by hydrogen bonds

- coiling or folding of primary structure (parallel polypeptide 'strands' joined by H bonds)

Tertiary protein structure:

- occurs when certain attractions are present between alpha helices and pleated sheets

- more coiling/folding to form a 3D shape held together by H bonds, ionic bonds; disulphide bonds (oxidation; lots of hydrogens covalently bonded together)

- e.g. globular protein - enzymes ->soluble in water; has alpha helix; spherical shape

- e.g. fibrous protein - collagen, keratin; each fibre is a helix coilded into another helix

Quarternary protein structure:

- is a protein consisting of more than one amino acid chain e.g. haemoglobin

- polypeptide sub units

- more than 1 tertiary structure

- held together by attraction of opposite charges (ionic bonding)

Biochemical test for protein

• Add 2cm^3 of unknown solution to a test tube
• Add an equal volume of sodium hydroxide (5%)
• Add 6 drops of copper sulphate solution
• Mix gently

Purple = positive

Blue = negative