1. Proteins What do we need proteins for?
What foods are good protein sources?
How do we test for the presence of proteins?

2. Primary structure The sequence of amino acids that forms the protein
Determined by the order of bases in DNA
Position and proportion of amino acids can vary

3. Secondary structure
Formed when the chain of amino acids coils or folds.
Forms either
an alpha helix
beta pleated sheet.
Hydrogen bonds give stability due to quantity.

4. Heating a protein causes denaturation
Tertiary structure
3D shape of a protein
Vital to its function
Bonds between R groups that stabilise the 3D shape:
Disulphide bonds
Ionic bonds
Hydrogen bonds
Hydrophilic and hydrophobic interactions
Heating a protein causes denaturation

5. Quaternary structure
Some proteins are made up of more than one polypeptide subunit joined together / or a polypeptide and an inorganic component
Examples include haemoglobin (4)and insulin(2)
Not all proteins have a quaternary structure

6. Classification of Proteins
Globular
Fibrous
Soluble
Metabolically active (involved in reactions)
Rolls up into balls (globules) Eg
Enzymes
Antibodies
Haemoglobin
Plasma proteins
(mostly α helix)
Insoluble
Structural
Forms fibres Eg
Collagen
Keratin
(mostly β pleating)

7. Functions of Proteins Actin and Myosin Antibodies Hormones Enzymes
(Immunoglobulins)
Hormones
Enzymes
Keratin
Haemoglobin
Collagen

8. Haemoglobin (globular, water soluble protein)
4 polypeptide subunits
(2 alpha and 2 beta).
Shape vital to function – to
carry oxygen from lungs to the
tissues
Most of structure is alpha helix
Haem group (prosthetic group), contains Fe2+ and is responsible for the colour
Each molecule binds 4 oxygen molecules 4 O₂

9. Did you know?

10. Collagen (Insoluble fibrous protein)
3 polypeptide chains, wound around each other.
Each of the three chains are coils, held together with Hydrogen bonds
Each collagen molecule forms strong covalent bonds (cross-links) with other collagen molecules.
Forms collagen fibrils. Many collagen fibrils together form a collagen fibre.

11. Why is Collagen so strong?
Glycine is small and this allows close packing between molecules
Collagen chains form a tight coil….they lie close to each other
Many hydrogen bonds between R groups hold 3 chains together very closely
Strong covalent bonds with adjacent molecules creating a very stable fibril
fibre composed of parallel fibril molecules and the ends of these parallel molecules are staggered which prevents line of weakness

13. Collagen provides mechanical strength in many areas including....
Walls of arteries
Tendons
Formation of bones
Cartilage and connective tissue
Used in cosmetic treatments e.g. Lip plumping

14. Making polypeptides and proteins
On ribosome (protein synthesis)
Uses mRNA
According to the code on the mRNA the amino acids are assembled in the right order and then joined by a peptide bond.

16. Breaking down proteins
Enzymes involved... Protease enzymes
Looking at two examples:
Hormone regulation
Ageing

18. Answers

19. ci. H bonds
ii.
Globular
Made of 2 types of polypeptide
Contains a non-protein/prosthetic/Haem group
Transport of oxygen

20. Roles of Proteins

21. Homework
Revision for Biological molecules test on Monday 9th March