AS Biology

1. AS Biology Module 1 Section 1.2 Enzymes

2. Specification

3. Enzymes • Enzymes are biological catalysts • This means they speed up reactions without being chemically changed themselves • They are GLOBULAR proteins • See notes on molecules to recall what these are

4. Enzyme Definitions • Active site • This is the region of the enzyme where catalysis occurs and substrates fit • Specificity • An enzyme may catalyse only one, or else lots of reactions. Its specificity determines this. An enzyme that catalyses one reaction is a highly specific enzyme. • Affinity • This is how strong an enzyme binds its substrates

5. Active Site • The substrate is held in the active site by a variety of bonds, such as hydrogen bonds and electrostatic interactions

6. Enzyme Definitions • Cofactors • These are non-protein chemical compounds that are bound to proteins and that are necessary for the protein to have biological activity. “Helper molecules” that are usually inorganic molecules. Common examples include NAD+, FAD, Coenzmye A, Mg2+ • Coenzymes • A loosely bound cofactor, usually an organic molecule • Prosthetic group • A tightly bound cofactor

7. Why do reactions take so long? • For a reaction to occur, say A and B turning into C • The rate will depend on how long A and B take to associate and then turn into C • This depends on how much energy you can supply to make this happen – the ACTIVATION ENERGY

8. Enzymes and Activation energy • Enzymes function by lowering the activation energy for reactions so that can be performed easier

9. Enzyme-Substrate complex • The enzyme binds both substrates, and lowers the reactions activation energy • This is called the ENZYME-SUBSTRATE COMPLEX • This allows the reaction to occur faster than if the reactants were floating about free in solution

10. Models of enzyme action • How enzymes work is quite an open area of debate in biology! • The main theories for how enzymes work are; • The lock and key hypothesis • The induced fit hypothesis

11. The lock-and-key hypothesis • In this model; • The reactants fit exactly into the enzyme active site like a key fits into a lock. Once the catalysis has occurred, the products are a different shape and fit than the reagents and so they fall out of the active site and the enzyme is free to start a new reaction

12. The induced fit hypothesis • In this model; • The reagents don’t fit exactly into the enzymes active site. But because enzymes are globular proteins with flexible shapes, the enzyme changes its active site shape to accommodate the reagents

13. How can we make enzymes work better? • Because enzymes are proteins they are easily affected by pH, temperature and concentrations of starting materials

14. The effect of heat on enzyme activity • Enzymes are held together by hydrogen bonds and other weak(ish) bonds • At temperature above body temp (37 oC), these bonds being to break and enzymes will no longer function. But from 0 to 37, the enzyme activity will steadily rise! Not all enzymes however are like this, it depends on each particular enzymes OPTIMUM TEMPERATURE!

15. The effect of pH on enzyme activity • As complex, folded proteins, enzymes are susceptible to changes in pH. Like with temperature, there is an OPTIMUM pH for every enzyme • For instance the enzymes in your stomach love being at pH 1 or 2. Yet enzymes that are found in your blood will only work well at pH 7.4-7.6. On either side of the optimum pH the enzyme rate will decrease to 0 as the pH is not optimum.

16. The effect of substrate concentration on enzyme activity • Substrate means that thing that will be reacted with and changed by the enzyme • As you put in more substrate, the enzyme will work and convert it to product! And this will happen in a directly proportional way until ALL the enzyme active sites are filled and the enzymes are working at peak rate.

17. The effect of enzyme concentration on enzyme activity • Amount of enzyme will also affect a reactions rate. As you put in more enzyme, the rate will increase proportionally as there is nothing to slow down the speed of the enzyme. • Eventually however, the amount of substrate will begin to limit the reaction and the graph will level off.

18. Summary

19. Enzyme Inhibition • Competitive inhibitors These bind to the active site of the enzyme and prevent substrates from binding and reacting. • Non-competitive inhibitors These bind anywhere on the enzyme EXCEPT the active site. This changes the shape of the enzyme and the active site and so stops substrate binding.

20. Enzyme Immobilisation • Enzymes are a multi-million pound business because they are cheap to make and can be used for a multitude of purposes • They can make reactions happen that would otherwise take hours or days to happen without the help of an enzyme • One way to increase the efficiency of enzyme catalysed reactions is to immobilise the enzymes on solid supports in such a way that their active site is easy to access

21. Methods of immobilisation

22. Why do we bother immobilising? • Immobilising an enzyme allows for cost effective usage of enzymes • Immobilising can lead to; • Increased enzyme stability • Increased pH tolerance • Increased temperature tolerance • It allows continuous flow operation compared to time consuming batch operation

23. Batch vs. Continuous culture

24. Problems with immobilising • Reduced enzyme efficiency in some cases as the steps to immobilise the enzymes can damage them • Sometimes the enzymes get attached the wrong way around which means that the active site cannot be accessed by the reagents

25. Lactose-free milk • An example of immobilised enzyme continuous culture is in the production of lactose free milk for people who suffer lactose intolerance or for cats

26. Clinistix • Medical diagnostic kits use immobilised enzymes to text for diabetes and kidney failure • Pregnancy tests also use immobilised enzymes that detect human gonadotrophin in urine