1. PROTEINS Have a wide range of functions; haemoglobin, antibodies & enzymes Amino acids are the monomers Twenty naturally occurring amino acids The order of the AA and the way they are folded dictates the function

2. Variable R group General Amino Acid Structure NH 2 COOH Central (α) carbon

3. Forming a dipepetide AA 1 and AA2 line up Amine next to carboxyl group Amine Grp ‘donates’ OH Carb. Grp ‘donates’ H Water is eliminated A dipeptide is formed

4. Forming a polypepetide 1000s of AAs link up Ribosomes convert AA to polypeptides A string of AA like this is PRIMARY STRUCTURE

5. Secondary Protein Structure Two types exist; alpha (α) helix beta (β)pleated sheets

6. Alpha (α) helix AA interact with each other The H on the NH grp is attracted to the O on the CO grp The H is slightly positive and the O is slightly negative A H bond forms between these two atoms

7. The H bonds that keep Alpha helices together are vulnerable to fluctuations in pH & temperature Hydrogen bonds are numerous…….. ……..individually weak!

8. Beta (β) pleated sheets Hydrogen bonds hold adjacent primary chains together

9. To go above secondary structure, proteins need more bond types; Disulphide bonds Adjacent cysteine AA Weak bond Broken by reducing agents Ionic bonds Forms between ionised amine & carboxylic grps Broken by pH extreme Hydrophobic Interactions Btwn non polar R-grps

10. TERTIARY PROTEIN STRUCTURE Classic example – MYOGLOBIN Folded into a precise 3D shape H bonds form between tryptophan, arginine & asparagine. Dulsulphide bonds with cysteine Ionic bonds & hdrophobic interactions also exist

11. Myoglobin – a tertiary Level protein

12. QUATERNARY PROTEIN STRUCTURE Classic examples – HAEMOGLOBIN COLLAGEN Globular proteins are involved in chemical reactions & are soluble molecules; haemoglobin Fibrous proteins have a structural role in biology; collagen

13. HAEMOGLOBIN made of 4 polypeptide chains two alpha chains two beta chains Hydrophobic R grps point into the molecule Hydrophilic R grps point out of the molecule This makes haemoglobin highly soluble

14. HAEMOGLOBIN each of the 4 chains has a haem group the haem group is not made of AA, but is an integral part of the protein – prosthetic grp. Each haem group contains an ion of iron (Fe 2+ ) Each haem binds with one molecule of oxygen (O 2 ) So each haemoglobin can carry O 8

15. Haemoglobin – a quaternary Level protein