2. Objectives Students should know : That enzymes act as catalysts lowering activation energy through the formation of enzymesubstrate complexes. The lock and key and induced fit models of enzyme action. Enzyme properties The properties of enzymes relating to their tertiary structure. Description and explanation of the effects of temperature, competitive and non-competitive inhibitors, pH and substrate concentration. Candidates should be able to use the lock and key model to explain the properties of enzymes. They should also recognise its limitations and be able to explain why the induced fit model provides a better explanation of specific enzyme properties

3. Enzymes are Biological catalysts Made of protein. Enzymes control chemical reactions that take place in the cytoplasm. Not used up during the reaction. Are specific. Require optimum conditions at which they work best

4. The minimum amount of energy needed to start the reaction, leading to the formation of a high energy intermediate = The Activation energy

5. Energy Progress of reaction Substrates Products High energy intermediate Activation energy Enzymes reduce the height of the energy barrier

6. Lock and Key enzyme + substrateenzyme-substrate complex enzyme + product

7. Active site The active site involves a small number of key residues that actually bind the substrates The rest of the protein structure is needed to maintain these residues in position

8. Enzymes can break substances down: animation

9. Example: starch digestion Starch Maltose

10. Or build larger molecules: Active site es

11. Induced Fit The enzyme moulds itself around the substrate molecule

12. Enzyme activity How fast an enzyme is working Rate of Reaction Rate of Reaction = Amount of substrate changed (or amount product formed) in a given period of time.

13. Rate of Reaction Enzyme activity Variable you are looking at

14. Enzyme activity Variables Temperature pH Substrate Concentration

15. Rate of Reaction Temperature 0203050104060 40 o C - denatures 5- 40 o C Increase in Activity <5 o C - inactive

16. Effect of heat on enzyme activty If you heat the protein above its optimal temperature bonds break meaning the protein loses it secondary and tertiary structure

17. Effect of heat on enzyme activty Denaturing the protein ACTIVE SITE CHANGES SHAPE SO SUBSTRATE NO LONGER FITS Even if temperature lowered – enzyme can’t regain its correct shape

18. Rate of Reaction pH 1 342 5 6 789 Narrow pH optima Disrupt Ionic bonds - Structure Effect charged residues at active site

19. Rate of Reaction Substrate Concentration

20. Rate of Reaction Substrate Concentration Active sites full- maximum turnover

21. elmhurst.edu

23. Digestive enzymes allow hydrolysis reactions to take place rapidly in the conditions found in the gut. Starch is broken down by amylases to glucose Proteins are broken down by proteases into amino acids Fats are broken down into fatty acids and glycerol

24. Why can humans digest starch but not cellulose?

25. Lactose intolerance At birth babies make lactase to digest milk sugar Some people stop making this enzyme when they get older They become Lactose intolerant

26. Problems If they eat milk products the lactose is not broken down The sugar stays in the gut. Water stays in the gut due to the sugar The person develops diarrhoea Bacteria digest the lactose, producing gas and causing pain Affected individuals must avoid lactose products

27. This powerpoint was kindly donated to www.worldofteaching.com www.worldofteaching.com