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ENZYMES A protein that allows chemical reactions to occur faster by lowering the activation energy. © 2007 Paul Billiet ODWS.

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Presentation on theme: "ENZYMES A protein that allows chemical reactions to occur faster by lowering the activation energy. © 2007 Paul Billiet ODWS."— Presentation transcript:

1 ENZYMES A protein that allows chemical reactions to occur faster by lowering the activation energy. © 2007 Paul Billiet ODWS

2 Chemical reactions Chemical reactions need an initial input of energy = THE ACTIVATION ENERGY © 2007 Paul Billiet ODWS

3 Reaction pathway © 2007 Paul Billiet ODWS

4 Making reactions go faster
Increasing the temperature make molecules move faster Enzymes can increase the rate of reactions without increasing the temperature. They do this by lowering the activation energy. © 2007 Paul Billiet ODWS

5 An enzyme controlled pathway
© 2007 Paul Billiet ODWS

6 Enzyme structure Enzymes are proteins They have a globular shape
A complex 3-D structure Human pancreatic amylase © Dr. Anjuman Begum © 2007 Paul Billiet ODWS

7 The active site One part of an enzyme, the active site, is particularly important The shape and the chemical environment inside the active site permits a chemical reaction to proceed more easily © H.PELLETIER, M.R.SAWAYA ProNuC Database © 2007 Paul Billiet ODWS

8 The substrate The substrate of an enzyme are the reactants that are activated by the enzyme Enzymes are specific to their substrates The specificity is determined by the active site © 2007 Paul Billiet ODWS

9 Enzyme may be used again Enzyme-substrate complex E S
Reaction coordinate © 2007 Paul Billiet ODWS

10 The Induced Fit Hypothesis
Some proteins can change their shape (conformation) When a substrate combines with an enzyme, it induces a change in the enzyme’s conformation The active site is then moulded into a precise conformation Making the chemical environment suitable for the reaction The bonds of the substrate are stretched to make the reaction easier (lowers activation energy) © 2007 Paul Billiet ODWS

11 The Induced Fit Hypothesis
Hexokinase (a) without (b) with glucose substrate This explains the enzymes that can react with a range of substrates of similar types © 2007 Paul Billiet ODWS

12 Factors affecting Enzymes
substrate concentration pH temperature inhibitors © 2007 Paul Billiet ODWS

13 Substrate concentration: Non-enzymic reactions
Reaction velocity Substrate concentration The increase in velocity is proportional to the substrate concentration © 2007 Paul Billiet ODWS

14 Substrate concentration: Enzymic reactions
Reaction velocity Substrate concentration Vmax Faster reaction but it reaches a saturation point when all the enzyme molecules are occupied. If you alter the concentration of the enzyme then Vmax will change too. © 2007 Paul Billiet ODWS

15 The effect of pH Optimum pH values Enzyme activity Trypsin Pepsin pH 1
3 5 7 9 11 © 2007 Paul Billiet ODWS

16 The effect of pH Extreme pH levels will produce denaturation
The structure of the enzyme is changed The active site is distorted and the substrate molecules will no longer fit in it © 2007 Paul Billiet ODWS

17 The effect of temperature
The rate of enzyme-controlled reactions increases as the temperature increases BUT at high temperatures proteins denature © 2007 Paul Billiet ODWS

18 The effect of temperature
Temperature / °C Enzyme activity 10 20 30 40 50 Q10 Denaturation © 2007 Paul Billiet ODWS

19 The effect of temperature
For most enzymes the optimum temperature is about 30°C Many are a lot lower, cold water fish will die at 30°C because their enzymes denature A few bacteria have enzymes that can withstand very high temperatures up to 100°C Most enzymes however are fully denatured at 70°C © 2007 Paul Billiet ODWS

20 Inhibitors Inhibitors are chemicals that reduce the rate of enzymic reactions. The are usually specific and they work at low concentrations. They block the enzyme but they do not usually destroy it. Many drugs and poisons are inhibitors of enzymes in the nervous system. © 2007 Paul Billiet ODWS

21 The effect of enzyme inhibition
Irreversible inhibitors: Combine with the functional groups of the amino acids in the active site, irreversibly. Examples: nerve gases and pesticides, containing organophosphorus, combine with serine residues in the enzyme acetylcholine esterase. © 2007 Paul Billiet ODWS

22 The effect of enzyme inhibition
Reversible inhibitors: These can be washed out of the solution of enzyme by dialysis. There are two categories. © 2007 Paul Billiet ODWS

23 The effect of enzyme inhibition
Competitive: These compete with the substrate molecules for the active site. The inhibitor’s action is proportional to its concentration. Resembles the substrate’s structure closely. Enzyme inhibitor complex Reversible reaction E + I EI © 2007 Paul Billiet ODWS

24 The effect of enzyme inhibition
Succinate Fumarate + 2H++ 2e- Succinate dehydrogenase CH2COOH CHCOOH COOH CH2 Malonate © 2007 Paul Billiet ODWS

25 The effect of enzyme inhibition
Non-competitive: These are not influenced by the concentration of the substrate. It inhibits by binding irreversibly to the enzyme but not at the active site. Examples Cyanide combines with the Iron in the enzymes cytochrome oxidase. Heavy metals, Ag or Hg, combine with –SH groups. These can be removed by using a chelating agent such as EDTA. © 2007 Paul Billiet ODWS

26 Applications of inhibitors
Negative feedback: end point or end product inhibition Poisons snake bite, plant alkaloids and nerve gases. Medicine antibiotics, sulphonamides, sedatives and stimulants © 2007 Paul Billiet ODWS

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