1. Proteins

2. Have many roles in the body:
Enzymes
Hormones
Muscles
Antibodies
Form haemoglobin, hair, skin, nails etc
Composed of Carbon, Hydrogen, Oxygen & Nitrogen (some have S & P)
They are long polymers composed of amino acids

3. Amino Acids There are 20 naturally occurring amino acids Structure is:
R – group varies in different amino acids

4. Amino acids are linked together to form proteins
A condensation reaction takes place between the amino group of one aa and the carboxyl group of another.
The bond formed is a PEPTIDE BOND

6. C C C C C C C C
glycine
glycine

7. PRIMARY STRUCTURE

8. Protein structure Primary Structure
ala – gly – cys – ala – phe – phe – cys – gly – ala -
The sequence of amino acids in the chain
Held together
by peptide bonds
Order of amino acids is important as
Determines the shape and therefore the function of the protein
Peptide bonds

9. Amino acids do not lie flat
Secondary Structure
Amino acids do not lie flat
Chains of amino acids fold to form helices and b pleated sheets held together by
H-bonds
H bonds

10. alpha helix

11. beta pleated sheet

12. Tertiary Structure Complex 3D shape of molecule
Occurs when polypeptide helix twists and folds around itself
Held together by hydrogen bonds -which are weak
ionic bonds -between R-groups with positive or negative charges, which are quite strong
disulphide bridges -covalent S-S bonds between two cysteine amino acids, which are strong.

15. tertiary structure

16. Quaternary Structure When a number of polypeptide chains link together
Example – haemoglobin has 4 polypeptide chains

17. Primary Protein Structure
The sequence of a chain of amino acids
Secondary Protein Structure
Occurs when the sequence of a chain of amino acids are linked by hydrogen bonds
Tertiary Protein Structure
Occurs when bonds form between alpha helices and pleated sheets
Quaternary Protein Structure
As a protein containing of more than one amino acid chain

18. Protein shape in relation to function
The final 3D structure of proteins results in 2 main classes of protein
Fibrous
Globular

19. Fibrous
Contain polypeptides that bind together to form long fibres or sheets
Physically tough
Insoluble in water
Tend to have a structural function
Eg collagen – the most widespread structural protein in the body. Gives strength to bones, tendons, skin and ligaments. 3 polypeptide chains twisted into a triple helix.

21. Collagen fibrils

24. Globular
Individual molecules with complex tertiary or quaternary structures
Spherical (globular) in shape
Most are soluble in water
Tend to have a biochemical rather than structural function
Eg enzymes, haemoglobin
Because the 3D structure is held together with weak bonds they are very susceptible to extremes of temperature (this can break the bonds and alter the shape of the protein)

25. A globular
protein

26. Haemoglobin Has a quaternary structure Made up of 4 polypeptide chains
It is a conjugated protein as each polypeptide chain is associated with an iron containing haem group
It role is to carry oxygen around the body

28. quaternary structure
polypeptide 1
polypeptide 2
polypeptide 4
polypeptide 3
haemoglobin

29. Conjugated proteins
These are proteins that are joined to other non-protein groups.
The non-protein group is called a prosthetic group.
Glycoprotein = protein + carbohydrate
Haemoglobin = 4 polypeptide chains, each with an iron containing haem group.

30. Primary Protein Structure
The sequence of a chain of amino acids
Secondary Protein Structure
Occurs when the sequence of a chain of amino acids are linked by hydrogen bonds
Tertiary Protein Structure
Occurs when bonds form between alpha helices and pleated sheets
Quaternary Protein Structure
A protein containing of more than one amino acid chain

31. Primary Protein Structure
The sequence of a chain of amino acids
Secondary Protein Structure
Occurs when the sequence of a chain of amino acids are linked by hydrogen bonds
Tertiary Protein Structure
Occurs when bonds form between alpha helices and pleated sheets
Quaternary Protein Structure
A protein containing of more than one amino acid chain