Topic 4: Chapter 5

1. Topic 4: Chapter 5 Enzymes – Part 2 Characteristics of Enzymes

2. Characteristics of Enzymes? • Enzymes • speed up chemical reactions • are required in minute amounts • are highly specific in their action • are affected by temperature • are affected by pH • Some catalyse reversible reactions • Some require co-enzymes • Are inhibited by inhibitors

3. (1) Enzymes Speed up chemical reactions Energy Activation Energy without enzyme Activation Energy with enzyme Substrate • By lowering the activation energy needed to start the reaction. Products: Time

4. (2) Enzymes are required in minute amounts Chemically unchanged Sucrase • Sucrose Glucose + Fructose • They remain chemically unchanged after catalysing the reactions. • The same enzyme molecules can be reused over again. • Therefore, only a small amount of enzyme is required to catalyse a large number of reactions

5. (3) Enzymes are highly specific Starch Maltose Amylase Maltose Glucose + Glucose Maltase • Each chemical reaction is catalysed by its own specific, unique enzyme. • This is due to every enzyme’s specific 3-d configuration. • How the shape of an enzyme affects its function can be explained by the “LOCK & KEY HYPOTHESIS”.

6. Lock & Key Hypothesis • Enzymes are proteins and each has an active site. • Active sites are depressions on the surface of enzyme molecules with specific shape and specific charges. • Active sites are formed due to the way the proteins are folded and held together by H-bonds.

7. Active Sites Lock & Key Hypothesis • Every active site has it’s own specific shape and charges. • It only allows substrates with a COMPLEMENTARY shape and charge to bind with it to form an Enzyme-Substrate Complex Substrate Enzyme-Substrate Complex Products + Enzyme Enzyme

8. Anabolic Reaction - Synthesis Catabolic Reaction - Hydrolysis

9. TheLock and KeyHypothesis • The substrate binds to a free enzyme with a complementary active site to form the enzyme-substrate complex • The enzyme-substrate complex brings about the necessary reactions • The product separates from the enzyme, leaving the enzyme molecule unchanged and free to combine again with more substrate molecules

10. (4) Enzymes are affected by temperature • Enzymes can function over a range of temperatures. • But all enzymes have their own optimum temperature.

11. Optimum temperature • The optimum temperature is the temperature at which the enzyme is most active, catalysing the largest number of reactions per second. • Different enzymes have different optimum temp. • Example: • most enzymes in the human body functions best at about 37-40oC, near body temperature. • Enzymes of thermophilic bacteria that live in hotsprings will have very high optimum temperatures.

12. How enzyme activity is affected by temperature NOTE: Describe the enzyme activity with respect to the Rate-Temperature Graph Increasing temp up to optimum temp. • At low temperature, enzymes are INACTIVE. • As temperature rises, the rate of enzyme activity increases (usually 2x as active for every 10oC rise). • Enzyme reaching maximum rate of activity at OT • Raising the temperature increases the kinetic energy supplied to the substrate and enzyme molecules. • This increases the no. of collisions between enzyme and substrate molecules. • Increasing the rate of formation of enzyme-substrate complex. • Rate of formation of the products increasesup till the optimum temperature

13. How enzyme activity is affected by temperature NOTE: Describe the enzyme activity with respect to the Rate-Temperature Graph Increasing temp beyond optimum temp. • Beyond the optimum temperature, rate of enzyme activity deceases. • Until it is completely denatured by the extreme heat • Increase in temperature increases the vibrations of the atoms in the enzymes. • Beyond the OT, the vibrations are so violent that they break the hydrogen bonds that hold the 3-D structrure in place. • The enzyme loses its shape and active site • The enzyme is DENATURED.

14. (4) Enzymes are affected by pH • Different enzymes have different optimum pH. • Enzymes are affected by the acidity or alkalinity of the solutions • M indicates the optimum pH when the rate of reaction is the highest

15. Different enzymes have different optimum pH Examples • Enzymes that work best at ACIDIC conditions • Renin and Pepsin: Found in the stomach • Enzymes that work best at ALKALINE conditions • Intestinal Enzymes • Enzymes that work best at NEUTRAL conditions • Amylase

16. Different enzymes have different optimum pH

17. How enzyme activity is affected by pH At pH slightly above or below the optimum • Enzyme activity reduces when the conditions are slightly more acidic or alkaline than the optimum pH • Slight changes in the pH brings about reversible changes • Changes can be restored by bringing enzyme back to the optimum pH

18. How enzyme activity is affected by pH At extreme pH conditions • Enzymes are DENATURED • Extreme changes in the pH causes: • A change in the charges at the active sites which repels the substrate molecules, preventing them from binding. • The irreversible alteration to the bonds that holds the shape of the enzyme. Enzyme thus loses its original 3-D structure. The active site loses its shape.

19. (5) Some enzymes catalyze reversible reactions Reactants Products A B C D + + Products Reactants • Some enzymes catalyse both reactions until equilibrium is reached. • Reactions will proceed in the direction where the products are constantly being removed • E.g formation of glucose during photosynthesis

20. (6) Some enzymes require co-enzymes • Some enzymes require co-enzymes to be bound to them before they can catalyse reactions • Co-enzymes • Small, non-protein, organic “helper” molecules

21. (7) Enzymes are inhibited by inhibitors Type 1 (Competitive) Substrate is prevented from binding to active site by inhibitor Type 2 (Non-competitive) Binding of inhibitor does not prevent the binding of substrate but slows down reaction speed