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  1. 1. Menon Lakshmi Suresh 1st MSC BPS
  2. 2. OBJECTIVES: • Define enzyme, substrate, active site • Explain enzyme substrate specificity (Lock and Key Model, Induced-Fit Model) • Describe the effects of temperature, pH, and substrate concentration on enzyme activity • Define co-enzymes and co-factors, give examples and describe their role in enzymatic activity. • Uses of Enzymes
  3. 3. • Enzymes are organic catalysts • All enzymes are composed of Proteins (tertiary and quaternary structures) • Because enzymes are composed of proteins, their shape is important to their function. (If you change the shape of the protein that composes the enzyme you alter or destroy the enzyme.)
  4. 4. • Enzymes are specific to which molecules they act upon. The substances they act upon are called substrates. • Most enzymes end with the suffix –ase. Sucrase, Lactase, Maltase • For example the enzyme found in saliva which begins the chemical hydrolysis of amylose is called amylase. • Enzymes are not used up or destroyed in the reaction process and at the end of their reaction will bind with more substrate molecules and repeat the same chemical process. Therefore, small numbers of these molecules can have a great effect.
  5. 5. • Each enzyme is the specific helper to a specific reaction – each enzyme needs to be the right shape for the job – enzymes are named for the reaction they help • sucrase breaks down sucrose • proteases breakdown proteins • lipases breakdown lipids • DNA polymerase builds DNA
  6. 6. • Enzymes affect the rates of reactions by lowering the amount of energy of activation required for the reactions to begin. Therefore processes can occur in living systems at lower temperatures or energy levels than it would require for these same reactions to occur without the enzymes present.
  7. 7. • Enzymes work by weakening bonds which lowers activation energy
  8. 8. 8 Free Energy Progress of the reaction Reactants Products Free energy of activation Without Enzyme With Enzyme
  9. 9. Enzymes aren’t used up • Enzymes are not changed by the reaction – used only temporarily – re-used again for the same reaction with other molecules – very little enzyme needed to help in many reactions enzyme substrate product active site
  10. 10. • The substance (reactant) an enzyme acts on is the substrate Enzyme Substrate Joins
  11. 11. • A restricted region of an enzyme molecule which binds to the substrate. EnzymeSubstrate Active Site
  12. 12. How Enzymes Bind to Substrates • There are two proposed methods by which enzymes bind to their substrate molecules: a. Lock and Key Model b. Induced-Fit Model
  13. 13. Enzymes • Lock and Key Analogy: lock = enzyme, key = substrate.
  14. 14. It’s shape that matters! • Lock & Key model – shape of protein allows enzyme & substrate to fit – specific enzyme for each specific reaction
  15. 15. 1 2 3
  16. 16. Induced-Fit Model The induced model states that the substrate binds to the active site and induces or causes a change in shape of the active site so that it is a complimentary fit. This model explains why some enzymes can act on more than one substrate. S1 S2 S3 P1 P1SUBSTRATE MOLECULES ENZYME SUBSTRATE COMPLEX Products Active site in inactive state Substrate induces a change in active site so that it is complimentary The active site of the enzyme returns to the inactive state after the products are released and now can react with more substrate. ENZYME S1
  17. 17. Induced Fit
  18. 18. 18 Induced Fit • A change in the configuration of an enzyme’s active site (H+ and ionic bonds are involved). • Induced by the substrate. Enzyme Active Site substrate induced fit
  19. 19. 19 What Affects Enzyme Activity? • Three factors: 1. Environmental Conditions 2. Cofactors and Coenzymes 3. Enzyme Inhibitors
  20. 20. 1. Environmental Conditions 1. Extreme Temperature are the most dangerous - high temps may denature (unfold) the enzyme. 2.pH (most like 6 - 8 pH near neutral) 3.Ionic concentration (salt ions)
  21. 21. Environmental Factors Which Affect Enzyme Activity: Temperature All enzymes have an optimum temperature at which they work best. If you observe the enzyme’s activity below the specific temperature it will steadily increase until it reaches the optimum. After the optimum temperature is reached the enzymes activity drops dramatically due to denaturing. Depending on the species, the range of optimum activity is very broad. Above is a comparison of human enzyme activity with that of bacteria found in hot springs and oceanic vents.
  22. 22. Environmental Factors Which Affect Enzyme Activity: pH All enzymes have an optimum pH at which they work best. If the pH falls below or rises above the optimum value, enzymatic activity decreases as a result of denaturing. In the human body’s digestive tract there are variations in pH from area to area. The stomach’s juices’ pH is around 2 (acidic), the enzyme pepsin found in the gastric juices has optimum activity at a pH of 2. The small intestine’s juice’s pH is around 8 (basic). The enzyme trypsin found in the small intestine’s juices has optimum activity at a pH of 8.
  23. 23. Environmental Factors Which Affect Enzyme Activity: Substrate Concentration The concentration of substrate also has an affect on the rate of enzyme activity. If the concentration of substrate is increased while the concentration of enzyme is constant, the level of enzyme activity will increase until a point of saturation is reached. At this point there are no enzymes available to react with excess substrate and the rate of the reaction stabilizes. No matter if you continue to add substrate, the reaction rate will not increase! Increasing Substrate Concentration Rate of Reaction Point of Saturation, all active sites are filled with substrate.
  24. 24. 2. Cofactors and Coenzymes • Some enzymes require another organic molecule or substance to be present before they can function. • These organic molecules or substances are called Co- enzymes or Co-factors. • Co-enzymes are organic molecules (usually vitamins) • Co-factors are inorganic substance (minerals). This is one of the reasons it is so important to eat a well balanced diet.
  25. 25. • For example, Vitamin K is necessary for the enzyme responsible for blood clot formation. A lack of vitamin K leads to easy bruising and prolonged bleeding when injuries occur. • Calcium is a co-factor which is required by several enzymes for their activation.
  26. 26. 3. Enzymatic inhibition. To regulate enzyme activity, there must be some form of prevention of binding of substrate with active site. There are two forms of inhibition: 1. Competitive inhibition 2. Noncompetitive inhibition
  27. 27. 27 Two examples of Enzyme Inhibitors a. Competitive inhibitors: are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site. Enzyme Competitive inhibitor Substrate
  28. 28. 28 b.Noncompetitive inhibitors: Inhibitors that do not enter the active site, but bind to another part of the enzyme causing the enzyme to change its shape, which in turn alters the active site. Enzyme active site altered Noncompetitive Inhibitor Substrate