Section 1.2 enzymes


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Section 1.2 enzymes

  1. 1. Module 1Section 1.2EnzymesAS Biology
  2. 2. Specification
  3. 3. Enzymes Enzymes are biological catalysts This means they speed up reactions withoutbeing chemically changed themselves They are GLOBULAR proteins See notes on molecules to recall what these are
  4. 4. Enzyme Definitions Active site This is the region of the enzyme where catalysisoccurs and substrates fit Specificity An enzyme may catalyse only one, or else lots ofreactions. Its specificity determines this. An enzymethat catalyses one reaction is a highly specificenzyme. Affinity This is how strong an enzyme binds its substrates
  5. 5. Active Site The substrate is held in the active site by avariety of bonds, such as hydrogen bonds andelectrostatic interactions
  6. 6. Enzyme Definitions Cofactors These are non-protein chemical compounds thatare bound to proteins and that are necessary for theprotein to have biological activity. “Helpermolecules” that are usually inorganic molecules.Common examples include NAD+, FAD, CoenzmyeA, Mg2+ Coenzymes A loosely bound cofactor, usually an organicmolecule Prosthetic group
  7. 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 toassociate and then turn into C This depends on how much energy you cansupply to make this happen – the ACTIVATIONENERGY
  8. 8. Enzymes and Activation energy Enzymes function by lowering the activationenergy for reactions so that can be performedeasier
  9. 9. Enzyme-Substrate complex The enzyme binds both substrates, and lowersthe reactions activation energy This is called the ENZYME-SUBSTRATECOMPLEX This allows the reaction to occur faster than if thereactants were floating about free in solution
  10. 10. Models of enzyme action How enzymes work is quite an open area ofdebate in biology! The main theories for how enzymes work are; The lock and key hypothesis The induced fit hypothesis
  11. 11. The lock-and-key hypothesis In this model; The reactants fit exactly into the enzyme activesite like a key fits into a lock. Once the catalysishas occurred, the products are a different shapeand fit than the reagents and so they fall out ofthe active site and the enzyme is free to start anew reaction
  12. 12. The induced fit hypothesis In this model; The reagents don’t fit exactly into the enzymesactive site. But because enzymes are globularproteins with flexible shapes, the enzymechanges its active site shape to accommodatethe reagents
  13. 13. How can we make enzymes workbetter? Because enzymes are proteins they are easilyaffected by pH, temperature and concentrationsof starting materials
  14. 14. The effect of heat on enzymeactivity Enzymes are held together by hydrogen bonds andother weak(ish) bonds At temperature above body temp (37 oC), thesebonds being to break and enzymes will no longerfunction. But from 0 to 37, the enzyme activity willsteadily rise! Not all enzymes however are like this, itdepends on each particular enzymes OPTIMUM
  15. 15.  As complex, folded proteins, enzymes are susceptibleto changes in pH. Like with temperature, there is anOPTIMUM pH for every enzyme For instance the enzymes in your stomach love beingat pH 1 or 2. Yet enzymes that are found in your bloodwill only work well at pH 7.4-7.6. On either side of theoptimum pH the enzyme rate will decrease to 0 as thepH is not optimum.The effect of pH on enzyme activity
  16. 16.  Substrate means that thing that will be reactedwith and changed by the enzyme As you put in more substrate, the enzyme willwork and convert it to product! And this willhappen in a directly proportional way until ALL theenzyme active sites are filled and the enzymesThe effect of substrate concentrationon enzyme activity
  17. 17.  Amount of enzyme will also affect a reactionsrate. As you put in more enzyme, the rate willincrease proportionally as there is nothing to slowdown the speed of the enzyme. Eventually however, the amount of substrate willbegin to limit the reaction and the graph will leveloff.The effect of enzyme concentration onenzyme activity
  18. 18. Summary
  19. 19. Enzyme Inhibition Competitive inhibitorsThese bind to the active site of the enzyme and preventsubstrates from binding and reacting. Non-competitive inhibitorsThese bind anywhere on the enzyme EXCEPT the activesite. This changes the shape of the enzyme and theactive site and so stops substrate binding.
  20. 20. Enzyme Immobilisation Enzymes are a multi-million pound businessbecause they are cheap to make and can beused for a multitude of purposes They can make reactions happen that wouldotherwise take hours or days to happen withoutthe help of an enzyme One way to increase the efficiency of enzymecatalysed reactions is to immobilise the enzymeson solid supports in such a way that their activesite is easy to access
  21. 21. Methods of immobilisation
  22. 22. Why do we bother immobilising? Immobilising an enzyme allows for cost effectiveusage of enzymes Immobilising can lead to; Increased enzyme stability Increased pH tolerance Increased temperature tolerance It allows continuous flow operation compared totime consuming batch operation
  23. 23. Batch vs. Continuous culture
  24. 24. Problems with immobilising Reduced enzymeefficiency in somecases as the steps toimmobilise theenzymes can damagethem Sometimes theenzymes get attachedthe wrong way aroundwhich means that theactive site cannot beaccessed by the
  25. 25. Lactose-free milk An example ofimmobilised enzymecontinuous culture is inthe production of lactosefree milk for people whosuffer lactose intoleranceor for cats
  26. 26. Clinistix Medical diagnostickits use immobilisedenzymes to text fordiabetes and kidneyfailure Pregnancy tests alsouse immobilisedenzymes that detecthuman gonadotrophinin urine