- There are 20 types of amino acids
- A protein may have 500 Aas in it.
- Polymers are long chains of repeating subunits - monomers
- Proteins are long chains of amino acids
- They always contain C, H, O and N
- Occasionally they contain S - cysteine; and Fe - haemoglobin
- Essential Aas are those which cannot be produced by the body and must be obtained by diet
- Formation of a protein involves a condensation reaction
- Aa - polypeptides - peptones - proteoses - proteins
- Some are fibrillar/fibrous - long chains that are straight and insoluble as the external R groups are non-polar. They have structural functions.
- Some are globular - round and soluble and have metabolic functions e.g. enzymes
- Can also be simple - only Aas present; or conjugated - Aas plus a non protein prosthetic group
- Primary structure - the number and sequence of Aas joined by peptide bonds
- Secondary structure - folding of chains into a helix or pleated sheet due to hydrogen bonds between the Aas. Several polypeptide chains together form either an alpha helix - coiling of the polypeptide chain is maintained by H bonds at each peptide link. Structural proteins such as keratin twist to form a two stranded helix whereas collagen forms a three stranded helix. Chains are linked by cross bridges and are very stable. Fibres provide strength and flexibility. Beta pleat - sheets provide flexibility
- Tertiary structure - secondary structure is further folded to form a coiled 3D structure. H bonds, disulphide bridges and ionic bonds involved. Hydrophobic side chains on the non-polar Aas are pushed towards the inside of the molecule, while hydrophilic side chains protrude to the outside.
- Quaternary structure - some proteins are made of more than one polypeptide chain such as haemoglobin
- PROTEIN TEST (buiret) - add a few cm cubed of sodium hydroxide to the protein solution. Add fresh 1% copper sulphate solution drop by drop. Look for a purple colouration.
- Uses of proteins include - insulation, hormones, receptors, carriers, channels/pores, enzymes and structural support
- Chemical reactions within a cell are known as metabolism
- Synthetic - building up; anabolic, e.g. A+B -> AB
- Breaking down - catabolic, e.g. AB -> A + B
- All reactions require enzymes
- Energy changes occur when two reactants collide forming an intermediate activated complex/transition state and then form products.
- If the potential energy in the reactants is greater than that in the products then energy is released - exergonic
- If a supply of energy is needed to get the potential energy of the products above that of the reactants - endergonic
- Energy needed for the formation of the activated complex is the activation energy