Proteins

• Building block of a protein=amino acids
• Amino acids are monomers that are joined in a sequence to form a protein
• The sequence of the amino acids determines the protein+its function
• Structure of an amino acid: amino group, carboxyl group, residual group
• Each of the 20 different amino acids have a different residual group

• A protein is a polymer of amino acids 
• Two amino acids are joined together by a condesation reaction to form a peptide bond
• The bond can be broken by hydrolysis, which involves adding water.
• When a larger chain of amino acids is formed=polypeptide

• Primary structure: seqeunce, type+number of amino acids in the chain. The structure+amino acids present determine the protein's function.
• Secondary structure:
• Chain takes a particular shape by folding or coiling as a result of the bonds formed between amino acids. Order of amino acids determines where bonds are formed=what shape occurs.
• Two forms of secondary folding: alpha helix and the beta pleated sheet. Alpha helix=held in place by H bonds between amino acids from different parts of the chain. Beta pleated sheet=folds in a concertina like way, H bonds connect to adjacent pleated sheet.

• Tertiary structure: 3D shape of protein molecule=further coiled or twisted into a more complex shape. Two types of tertiary structure: globular and fibrous
• Globular: when protein folds to form 3D shape=important in metabolic processes=enzymes=have specific active site for subsrate to bind too
• Fibrous: protein twists into a long thin structure, has important structural roles: keratin-hair, collagen in skin.

• Globular and fibrous proteins have a no.of different type of bonds to stabilise the molecule:H bonds, Ionic bonds, hydrophobic interations and disuphide bonds.
• H bond: attraction between slight + charge of a group and slight - charge of another
• Ionic bond: attraction between + charged R group of an amino acid and - charged R group of another.
• Hydrophobic interaction: association between hydrophobic R groups of amino acids (where H2O is excluded).
• Disulphide bond: Covalent bond between sulfur atoms of two R groups.

• Some proteins=made of more than 1 polypeptide chain
• Two or more chains are held together+function as a whole
• Protein will not function unless all subunits are together
•  Haemoglobin: quaternary structure+haem prothestic group (inorganic ion)
• Conjugated protein: globular protein with a prosthetic group

Feature                                      Haemoglobin                      Collagen

Type of protein stucture            globular                               fibrous

No.of polypeptides                          4                                         3

3D structure                            folded into ball                      twisted into long fibres

Helical structure                    right-handed alpha                  left-hand

Solubility in water                    soluble                                  insoluble

Types of amino acids              Most of the 20                       Just 3 amino acids

Prosthetic group                       haem                                    none

Role                                     transport of 02                         provides strength in many areas of the                                                                                                body: cartilage, bone, elasticity of skin