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  1. 1. Enzymes<br />By: Chen Dewei (2P304)<br />
  2. 2. Introduction of Enzymes<br />Biological catalysts which speed up biological reactions by lowering the activation energy required for them to take place<br />Mostly made up of proteins<br />Not used up or chemically changed at the end of the biological reaction<br />
  3. 3. Introduction of Enzymes (Cont.)<br />Can be used again and again<br />Produced only when needed<br />Catalyse reversible reactions<br />E + S ⇌ ES -> EP ⇌ E + P (E= Enzyme, S= Substrate, P=Product)<br />
  4. 4. Enzyme-Catalysed Reactions<br />Anabolic reactions<br />Synthesis of simpler substances into complex ones<br />Amino acids -> Polypeptides -> Proteins<br />Catabolic reactions<br />Breakdown of complex substances into simpler ones<br />Hydrogen peroxide -> Oxygen + Water<br />2H2O2-> O2 + 2H2O<br />To prevent the poisonous effect of hydrogen peroxide<br />
  5. 5. Classification of Enzymes<br />Hydrolases (Hydrolysis)<br />Catalyse hydrolytic reactions in the body (eg. Of digestion)<br />Oxidoreductoases (Oxidation – Reduction)<br />Transferases (Transfer groups of atoms)<br />Lyases (Add/Remove atoms to/from a double bond)<br />Isomerases (Rearrange atoms)<br />Ligases (Combine molecules using ATP)<br />
  6. 6. Types of Hydrolases<br />Carbohydrases<br />Digest carbohydrates<br />Amylase (starch)<br />Maltase (maltose)<br />Sucrase (sucrose)<br />Proteases<br />Digest proteins<br />Pepsin<br />Erepsin<br />Lipases<br />Digest fats<br />Lipase<br />
  7. 7. Characteristics of Enzymes<br />Speed up chemical reactions<br />Small amount is needed to catalyse a reaction because enzymes can be used again and again<br />The shapes of the active sites make enzymes highly specific, meaning they can only interact with 1 type of substrate to form an enzyme-substrate complex<br />Presented using the ‘lock and key’ hypothesis<br />
  8. 8. “Lock and Key” Hypothesis<br />The active site of an enzyme molecule = lock; substrate molecule that the enzyme acts on = key<br />When the enzyme and substrate molecules are bound together, they form an enzyme-substrate complex<br />Substrate molecule is subsequently converted into products<br />Product molecules leave the active site<br />Enzyme molecule is free to bind with more substrate molecules<br />
  9. 9. “Induced Fit” Model<br />Enzyme molecule can undergo adjustments at its active site<br />Binds more tightly with substrate molecule<br />Facilitates binding at active site and speeds up rate of chemical reaction<br />
  10. 10. Temperature<br />pH<br />Concentrations of substrates in enzymatic reactions<br />Factors Which Affect Enzyme Activity<br />
  11. 11. Temperature<br />Optimum temperature – the temperature at which an enzyme is the most active (can catalyse the most number of reactions per second)<br />Rise in temperature (till optimum) -> Increase in enzyme activity<br />Kinetic energy of particles increases<br />Increases the chance of substrate molecules fitting into the active sites of enzyme molecules<br />More rapid formation of enzyme-substrate complexes<br />Increase in formation of products<br />
  12. 12. Temperature (Cont.)<br />When temperature exceeds the optimum temperature of enzyme activity, it starts to fall rapidly<br />H-H bonds in enzymes break, leading to the denaturation of enzymes<br />Unique 3-dimensional structure lost<br />Denaturation is irreversible<br />
  13. 13. pH<br />Optimum pH = maximum activity<br />Most enzymes lose their abilities to catalyse reactions at pH 3 and 11<br />Extreme changes in pH of a solution will denature the enzyme, just like temperature<br />
  14. 14. pH (cont.)<br />Slight changes in pH is enough to change the electrostatic charges of the active site of enzyme and substrate<br />Electrostatic repulsion occurs<br />Inhibits the formation of enzyme-substrate complex<br />
  15. 15. Substrate and Enzyme Concentrations<br />Substrate concentration increases -> rate of reaction increases<br />Saturation of enzyme molecules (all being made use of)<br />Reaction cannot take place<br />Increase in enzyme concentration will increase the rate of reaction again<br />
  16. 16. Coenzymes<br />Not made up of protein (unlike enzymes)<br />Organic compounds<br />Bind with enzymes before the latter can catalyse reactions<br />
  17. 17. References<br />http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Enzymes.html<br />http://www.elmhurst.edu/~chm/vchembook/570enzymes.html<br />http://www.mrothery.co.uk/studentswork/student%20presentations/Enzyme%20Activity.ppt<br />
  18. 18. End of Presentation<br />