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ENZYMES. What can you recall from IGCSE? Define the following terms: 1.Anabolic reactions: 2.Catabolic reactions: 3.Metabolism: 4.Catalyst: 5.Metabolic.

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Presentation on theme: "ENZYMES. What can you recall from IGCSE? Define the following terms: 1.Anabolic reactions: 2.Catabolic reactions: 3.Metabolism: 4.Catalyst: 5.Metabolic."— Presentation transcript:


2 What can you recall from IGCSE?

3 Define the following terms: 1.Anabolic reactions: 2.Catabolic reactions: 3.Metabolism: 4.Catalyst: 5.Metabolic pathway: 6.Specificity: 7.Substrate: 8.Product: Reactions that build up molecules Reactions that break down molecules Combination of anabolic and catabolic reactions Sequence of enzyme controlled reactions Only able to catalyse specific reactions The molecule(s) the enzyme works on Molecule(s) produced by enzymes A substance that speeds up reactions without changing the produced substances

4 Naming enzymes: Intracellular enzymes Extracellular enzymes Recommended names Systematic name Classification number Work inside cells eg.DNA polymerase Secreted by cells and work outside cells eg. pepsin, amylase Short name, often ending in ase eg. creatine kinase Describes the type of reaction being catalysed eg. ATP:creatine phosphotransferase Eg

5 Timeline of enzyme discovery 1835: Breakdown of starch to sugar by malt 1877: Name enzyme coined to describe chemicals in yeast that ferment sugars 1897: Eduard Buchner extracted enzyme from yeast and showed it could work outside cells 1926: James B Sumner produced first pure crystalline enzyme (urease) and showed enzymes were proteins 1905: Otto Rohm exyracted pancreatic proteases to supply enzymes for tanning : Protein nature of enzymes finally established when digestive enzymes crystallised by John H Northrop 1946: Sumner finally awarded Nobel prize

6 Enzymes lower the activation energy of a reaction Final energy state of products Initial energy state of substrates Activation energy of uncatalysed reactions Activation energy of enzyme catalysed reaction Progress of reaction (time) Energy levels of molecules

7 Enzymes lower activation energy by forming an enzyme/substrate complex Substrate + Enzyme Enzyme/substrate complex Enzyme/product complex Product + Enzyme

8 In anabolic reactions enzymes bring the substrate molecules together. In catabolic reactions the enzyme active site affects the bonds in substrates so they are easier to break

9 Lock-and-key hypothesis assumes the active site of an enzyme is rigid in its shape How ever crystallographic studies indicate proteins are flexible.

10 The Induced-fit hypothesis suggests the active site is flexible and only assumes its catalytic conformation after the substrate molecules bind to the site. When the product leaves the enzyme the active site reverts to its inactive state.

11 Enzymes are globular proteins Active site has a specific shape due to tertiary structure of protein. A change in shape of the protein affects shape of active site and the function of the enzyme. Click to link to jmol interactive representation courtesy of University of Arizona

12 Characteristics of enzymes Only change the rate of reaction. They do not change the equilibrium or end products. Specific to one particular reaction Present in very small amounts due to high molecular activity: Turnover number = number of substrate molecules transformed per minute by one enzyme molecule Catalase turnover number = 6 x106/min

13 How would you measure the effect of an enzyme? Compare uncatalysed rate with catalysed. Enzymes can increase rate by a factor of between 10 8 to 10 26

14 Characteristics of enzymes Rate of enzyme action is dependent on number of substrate molecules present V max = maximum rate of reaction V max approached as all active sites become filled Some active sites free at lower substrate concentrations Substrate concentration Rate of Reaction (M)

15 Why do scientists measure the initial rate of reaction of enzyme-catalysed reactions? Rate of Reaction (M) Independent variable Initial rate of reaction They measure rate at start of reaction before any factors, eg. substrate concentration, have had time to change.

16 Rate of enzyme –catalysed reactions are affected by temperature. Temperature coefficient Q 10 : rate of reaction at (x + 10) o C Q 10 = rate of reaction at x o C Q 10 for between o C is 2

17 Enzymes denature at 60 o C Temperature Rate of reaction Rate doubles every 10 o C Enzyme denaturing and losing catalytic abilities Optimum temperature Some thermophilic bacteria have enzymes with optimum temperatures of 85 o C

18 pH affects the formation of hydrogen bonds and sulphur bridges in proteins and so affects shape. pepsin trypsin cholinesterase pH Rate of Reaction (M)

19 Enzymes in medicine Glucose oxidase Glucose Hydrogen peroxide peroxidase Dye: Blue---Green---Brown Dye changes according to amount of glucose Enzyme-linked immunosorbent assays (ELISAs) detect antibodies to infections. Glucose oxidase + peroxidase + blue dye on dipsticks to detect glucose in urine:

20 Now answer the exam questions The first question you will complete and then swap with your partner. You will then mark each others work using the provided mark-scheme. You must agree each others marking. The second question you will complete and mark your own and then I will mark it and see if I agree with your marking. The third question you will complete and I will mark it. You will then check my marking and we will agree a score. The total score for all three questions will be recorded.

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