Chap 10 enzyme
- 1. ENZYME Characteristic Mechanism Factors
- 2. Definition Enzymes are protein produced by the cells of living organism act as biological catalyst by controlling and accelerating the rate of biochemical reactions in the cell at fairly low temperatures. Without enzymes, biochemical reactions become too slow to maintain the life supporting process in an organism.
- 3. E A with enzyme Figure 5.5B Reactants Products E A without enzyme Net change in energy
- 4. Important Terms… The activation energy, E A Is the initial amount of energy needed to start a chemical reaction Is often supplied in the form of heat from the surroundings in a system
- 5. Cont… The active site Is the region on the enzyme where the substrate binds Figure 8.16 Substate Active site Enzyme (a)
- 6. Cont… Cofactors Are nonprotein enzyme helpers Coenzymes Are organic cofactors
- 7. Enzyme Inhibitors Competitive inhibitors Bind to the active site of an enzyme, competing with the substrate (b) Competitive inhibition A competitive inhibitor mimics the substrate, competing for the active site. Competitive inhibitor A substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme (a) Normal binding
- 8. Cont… Noncompetitive inhibitors Bind to another part of an enzyme, changing the function A noncompetitive inhibitor binds to the enzyme away from the active site, altering the conformation of the enzyme so that its active site no longer functions. Noncompetitive inhibitor (c) Noncompetitive inhibition
- 9. Competitive and noncompetitive inhibition
- 10. Types of enzymes Intracellular enzyme Enzymes that are produces in certain cells and remain to react in the cell These enzymes could exist either in cytoplasm (in organelles) or nucleus. Extracellular enzyme Some enzymes are produced by cell but then transported out of the cell for action outside the cell
- 11. How an enzyme works Enzyme (sucrase) Active site 1 2 3 Substrate (sucrose) Enzyme available with empty active site Substrate binds to enzyme with induced fit Substrate is converted to products 4 Products are released Glucose Fructose The enzyme is unchanged and can repeat the process Figure 5.6
- 12. Characteristics Enzymes generally act quickly the speed of reaction is usually stated in ‘turnover number’ (refer to the number of substrates) Enzymes are not damaged however, this does not mean that enzymes can be used repeatedly forever without replacement Enzymes can react in both direction Enzymes are specific each enzymes limited to one specific reaction that involved one specific substrate only
- 13. Cont… An enzymes molecule is usually bigger than its substrates All enzymes are proteins and not all protein are enzymes Enzymes are complex globular protein and three dimensional. Main function of enzymes Increase the rate of chemical reaction by lowering activation energy
- 14. Mechanisms of Enzymes There are 2 main hypothesis explaining the mechanism of enzyme action : The lock-and-key hypothesis The induced-fit hypothesis Simple mechanism
- 15. Lock-and-key hypothesis The hypothesis proposed that the active site and substrate are exactly complementary An enzyme is a large globular protein with specific three dimensional shape. It has a site called the active site . In the lock-and-key hypothesis, the shape of the substrate (‘key’) fits into the active site of the enzyme (‘lock’) forming and enzyme-substrate complex Reaction takes place and products are formed and released
- 16. Induced-fit hypothesis It is a modified version of the lock-and-key hypothesis The hypothesis suggested that active site is flexible and is not exactly complementary to the shape of the substrate An enzyme collides with the substrate molecule. The substrate binds to the active site The binding induces a slight change in the shape of the enzyme to enclose the substrate making the fit more precise.
- 17. factors Any factors that affect the activity of an enzyme will change the rate of the reaction catalysed by that enzyme Enzyme characteristic are affected by several factors such as temperature, pH, substrate and enzyme concentration.
- 18. The effect of Temperature At lower temperature, enzymes are not active As the temperature rises, the substrate and the enzyme molecules move rapidly and are more likely to collide The increase in temperature to a specific level can increase the rate of the enzyme activity until the optimum temperature rate . After the optimum temperature the enzymes activities decreased and totally stopped at temperature of ±60 o C
- 19. The effect of pH All enzymes have a specific optimum pH at which they function most efficiently Most enzyme act at a pH in range of 5 – 9, and reactions most efficiently at a pH of 7 The small change in pH can produce a large effect on enzyme activity A pH that is extreme usually destroy enzymes
- 20. Cont… However, there are exceptions for certain enzymes such as: Pepsin pH 1.5 – 2.5 (acidic) Rennin pH 8.5 (alkaline)
- 21. The effect of Enzyme Concentration The rate of an enzyme-catalysed reaction is directly proportional to the concentration of the enzymes if substrates are present in excess concentration and no other factors are limiting
- 22. The effect of Substrate Concentration Increasing the substrate concentration can give a increasing in reaction rate At lower concentrations the rate increase in direct proportion to the substrate concentration At higher substance concentration the rate of reaction becomes constant
- 23. classification Enzymes can be classified by the kind of chemical reaction catalyzed: Hydrolases Lyases Isomerase Ligases Transferases Oxidoreductase This classification system introduced in 1961 by IUB (International Union of Biochemistry)