1. Enzyme action. Learning: To explain how enzymes speed up rates of reaction. Doing: Enzyme investigation How do enzymes work – lock and key and induced fit. Q and A!!!!!

2. What do you know about enzymes? 5 key things – good 7 key things - fabulous 10 key things – genius!

3. So what are enzymes all about? Enzymes are generally globular proteins that act as biological catalyst. They speed up reactions within the body by lowering the activation energy. What is activation energy? A ball will not roll down a hill unless pushed!!!! Energy is released as the reactants form products making free energy negative.

4. Enzyme structure – it’s a quaternary protein. Large 3D proteins. Only a small area is functional and therefore useful, it is know as the active site. The active site is made up of a few AA and forms a dent or depression in the enzyme. (Pg 31) The enzyme is specific to a substrate, although some may bind with closely related substrates (rare but does happen). Enzymes will catalyse only one type of reaction e.g. Amylase breaks down starch to maltose.

5. Lock and Key model – this is the one you should know! Emil Fischer in 1894 described enzymes and substrates like a lock and key. A substrate will only fit the active site of one enzyme. It suggests that an enzyme is a rigid structure which cannot be altered.... BUT.... It has been observed that other molecules can bind with enzymes in other places which aren’t the active site. This suggests that this model is not perfect!

6. The induced fit model – this is more like it! Enzymes can change their shape to fit the substrate into the active site. The shape changes can expose the active site to allow the substrate into it. Some enzymes have been known to engulf the substrates to stop water being present in the reaction. The enzyme can put strain on the substrate and cause weakness in it’s bonds, this makes it more reactive to the other substrate and lowers the activation energy!

7. Questions! Are enzymes used up in a reaction? Do they change biologically? Can they change shape? How do they lower the activation energy? If you change an AA in the active site what will happen? What effects enzyme action?

8. Factors effecting enzyme activity Learning: To explain how different factors effect enzyme activity. Doing: Graphs – using the keywords.

9. How can we measure an enzyme reaction? Usual ways of measuring enzyme reactions are the amount of time for the maximum amount of product to be formed and the time taken for a substrate to disappear.

10. What does this graph show – standard reaction – no factor effecting Use the keywords to describe and explain the pattern in the graph. Enzyme, substrate, active site, reactant, product, enzyme substrate complex Why does the reaction slow as it reaches the end of the reaction?

11. Check your answer 1)Lots of substrate present so easy to come into contact with the active sites of enzyme. 2)All enzyme active sites are filled so lots of product is being formed, lots of enzyme-substrate complexes. 3)The amount of substrate decreases as the amount of product increases. 4)Substrate molecules are less able to come into contact with active sites as they are full. Also the substrate can get in the way. 5)The amount of product slows until it stops as all the substrate has been turned into product.

12. Factor effecting – temperature. Describe and explain the graph Use the keywords: Enzyme, substrate, active site, reactant, product, kinetic energy, enzyme substrate complexes, denature, optimum.

13. Check your answer An increase in temperature increases the kinetic energy of the enzyme and substrates. As a result they are more likely to collide increasing the number of enzyme substrate complexes. This leads to an increase in product being formed. At the optimum the maximum amount of substrate is formed. When the temperature increases too much the enzyme denatures. This means that the shape of the enzyme and the active site changes, preventing the substrate from entering. Optimum temperature is often specific to the enzyme, all body enzymes have an optimum temp of up to 40C.

14. Factor effecting - pH Describe and explain the graph Use the keywords: Enzyme, substrate, active site, reactant, product, kinetic energy, enzyme substrate complexes, denature, optimum, bond breaking, change in charge.

15. Check your answer 1)Pepsin has an optimum pH of 3 and trypsin has an optimum pH of 6-7. 2)This means that the maximum number of E-S complex are formed and the maximum amount of product is formed. 3)Changes in pH result in the enzyme denaturing. 4)This is because pH changes the charges and the substrate cannot become attached. 5)The pH change also causes the bonds in the tertiary structure break, changing the shape of the active site. 6)As a result it cannot form e-s complexes and no product is formed.

16. Substrate concentration Describe what happens as the substrate concentration increases Keywords: Enzyme, substrate, active site, reactant, product, v max, plateau, enzyme substrate complex.

17. Check your answer The enzyme amount is fixed and the substrate is slowly added the rate of reaction increases in proportion to amount of substrate added. The increase is slow to start as not all of the active sites are filled as there is not enough substrate. The rate of reaction levels off or plateaus at the v max. This is when all of the active sites are filled by substrate and no more enzyme-substrate complexes can form. Once the reaction reaches the Vmax the addition of any more substrate will have no effect on the reaction.