1. Menu 1 CH. 6 Factors Affecting ENZYME Activity

2. Menu 2 Catabolic and Anabolic Reactions  The energy-producing reactions within cells generally involve the breakdown of complex organic compounds to simpler compounds. These reactions release energy and are called catabolic reactions.  Anabolic reactions are those that consume energy while synthesizing compounds.  ATP produced by catabolic reactions provides the energy for anabolic reactions. Anabolic and catabolic reactions are therefore coupled (they work together) through the use of ATP.  Diagram: next slide

3. ATPADP + P i Energy Menu An anabolic reaction A catabolic reaction Catabolic and Anabolic Reactions

4. Menu 4 Enzymes Lower Activation Energy Energy Supplied Energy Released Activation energy without enzyme Activation energy with enzyme Enzymes lower the amount of activation energy needed for a reaction. Menu

5. Substrate Enzyme Active Site Enzyme-Substrate Complex Product Enzyme 1 2 3 Enzymes Enzymes are organic catalysts. Menu Cofactor/Coenzyme

6. Menu 6 Enzymes  Catalysts are substances that speed up chemical reactions. Organic catalysts (contain carbon) are called enzymes.  Enzymes are specific for one particular reaction or group of related reactions.  Many reactions cannot occur without the correct enzyme present.  They are often named by adding “ASE" to the name of the substrate. Example: Dehydrogenases are enzymes that remove hydrogen.

7. Menu 7 Induced Fit Theory – Most current  An enzyme-substrate complex forms when the enzyme’s active site binds with the substrate like a key fitting a lock.  The substrate molecule does not fit exactly in the active site. This induces a change in the enzymes conformation (shape) to make a closer fit.  After the reaction, the products are released and the enzyme returns to its normal shape.  Only a small amount of enzyme is needed because they can be used repeatedly.

8. Menu 8 Rate of Reaction  Reactions with enzymes are up to 10 billion times faster than those without enzymes.  Enzymes typically react with between 1 and 10,000 molecules per second. Fast enzymes catalyze up to 500,000 molecules per second.  Substrate concentration, enzyme concentration, Temperature, and pH affect the rate of enzyme reactions.

9. Menu 9 Substrate Concentration  At lower concentrations, the active sites on most of the enzyme molecules are not filled because there is not much substrate. Higher concentrations cause more collisions between the molecules. With more molecules and collisions, enzymes are more likely to encounter molecules of reactant.  The maximum velocity of a reaction is reached when the active sites are almost continuously filled. Increased substrate concentration after this point will not increase the rate. Reaction rate therefore increases as substrate concentration is increased but it levels off. Substrate Concentration Rate of Reaction Enzyme Active Site is Saturated

10. Menu 10 Enzyme Concentration  If there is insufficient enzyme present, the reaction will not proceed as fast as it otherwise would because there is not enough enzyme for all of the reactant molecules.  As the amount of enzyme is increased, the rate of reaction increases. If there are more enzyme molecules than are needed, adding additional enzyme will not increase the rate. Reaction rate therefore increases as enzyme concentration increases but then it levels off. Enzyme Concentration Rate of Reaction Even when adding more enzymes, there isn’t any more available substrate to create product at a faster rate

11. Menu 11 Effect of Temperature on Enzyme Activity 30 40 50 Rate of Reaction Temperature

12. Menu 12 Effect of Temperature on Enzyme Activity 30 40 50 Rate of Reaction Temperature Increasing the temperature causes more collisions between substrate and enzyme molecules. The rate of reaction therefore increases as temperature increases.

13. Menu 13 Effect of Temperature on Enzyme Activity 30 40 50 Rate of Reaction Temperature Enzymes denature when the temperature gets too high. The rate of reaction decreases as the enzyme becomes nonfunctional.

14. Menu 14 Temperature  Higher temperature causes more collisions between the atoms, ions, molecules, etc. It therefore increases the rate of a reaction – “Turnover Rate”. More collisions increase the likelihood that substrate will collide with the active site of the enzyme.  Above a certain temperature, activity begins to decline because the enzyme begins to denature (unfold).  The rate of chemical reactions therefore increases with temperature but then decreases. 30 40 50 Rate of Reaction Temperature

15. Menu 15 Denaturation  If the hydrogen bonds within an enzyme are broken, the enzyme may unfold or take on a different shape. The enzyme is denatured.  A denatured enzyme will not function properly because the shape of the active site has changed.  If the denaturation is not severe, the enzyme may regain its original shape and become functional.  The following will cause denaturation: –Heat –Changes in pH –Heavy-metal ions (lead, arsenic, mercury) –Alcohol –UV radiation

16. Menu 16 Effect of pH on Enzyme Activity 2 3 4 5 6 7 8 9 Rate of Reaction pH Pepsin Trypsin Each enzyme has its own optimum pH.

17. Menu 17 pH  Each enzyme has an optimal pH. Pepsin, an enzyme found in the stomach, functions best at a low pH. Trypsin, found in the intestine, functions best at a neutral pH.  A change in pH can alter the ionization of the R groups of the amino acids. When the charges on the amino acids change, hydrogen bonding within the protein molecule change and the molecule changes shape. The new shape may not be effective.  The diagram shows that pepsin functions best in an acid environment. This makes sense because pepsin is an enzyme that is normally found in the stomach where the pH is low due to the presence of hydrochloric acid. Trypsin is found in the duodenum (small intestine), and therefore, its optimum pH is in the neutral range to match the pH of the duodenum. 2 3 4 5 6 7 8 9 Rate of Reaction pH Pepsin Trypsin

18. Menu 18 Metabolic Pathways  Metabolism refers to the chemical reactions that occur within cells.  Reactions occur in a sequence and a specific enzyme catalyzes each step.

19. Menu 19 Metabolic Pathways enzyme 1enzyme 2enzyme 3enzyme 4 F enzyme 5 A B C D E Enzymes are very specific. In this case enzyme 1 will catalyze the conversion of A to B only. Notice that C can produce either D or F. This substrate has two different enzymes that work on it.

20. Menu 20 A Cyclic Metabolic Pathway B C D F A E A + F  B B  C  D D  F + E In this pathway, substrate “A” enters the reaction. After several steps, product “E” is produced.

21. Menu 21 Regulation of Enzymes  The next several slides illustrate how cells regulate enzymes. For example, it may be necessary to decrease the activity of certain enzymes if the cell no longer needs the product produced by the enzymes.

22. Menu 22 Regulation of Enzymes genetic regulation regulation of enzymes already produced competitive inhibition noncompetitive Inhibition (next slide) Cell can turn on DNA genes to build more enzymes when needed Cells can use certain chemicals to slow down existing enzymes

23. Menu 23 Competitive Inhibition In competitive inhibition, a similar-shaped molecule competes with the substrate for active sites.

24. Menu 24 Competitive Inhibition Active site is being occupied by competitive inhibitor This substrate cannot get into active site at this time

25. Menu 25 Noncompetitive Inhibition  Another form of inhibition involves an inhibitor that binds to an allosteric site of an enzyme. An allosteric site is a different location than the active site.  The binding of an inhibitor to the allosteric site alters the shape of the enzyme, resulting in a distorted active site that does not function properly. Active siteInhibitorAltered active site Enzyme

26. Menu 26 Noncompetitive Inhibition  The binding of an inhibitor to an allosteric site is usually temporary. Poisons are inhibitors that bind irreversibly. For example, penicillin inhibits an enzyme needed by bacteria to build the cell wall. Bacteria growing (reproducing) without producing cell walls eventually rupture.

27. Menu 27 Enzyme regulation by negative feedback inhibition is similar to the thermostat example. As an enzyme's product accumulates, it turns off the enzyme just as heat causes a thermostat to turn off the production of heat. Feedback Inhibition A B C D enzyme 1enzyme 2enzyme 3 The goal of this hypothetical metabolic pathway is to produce chemical D from A. B and C are intermediates. The next several slides will show how feedback inhibition regulates the amount of D produced.

28. Menu 28 Feedback Inhibition A B C D enzyme 1enzyme 2enzyme 3 X Enzyme 1 is structured in a way that causes it to interact with D. When the amount of D increases, the enzyme stops functioning. X The amount of B in the cell will decrease if enzyme 1 is inhibited. XX C and D will decrease because B is needed to produce C and C is needed to produce D.

29. Menu 29 A B C D X Feedback Inhibition enzyme 1enzyme 2enzyme 3 XX When the amount of D drops, enzyme 1 will no longer be inhibited by it. B CD B, C, and D can now be synthesized.

30. Menu 30 Feedback Inhibition A B C D enzyme 1enzyme 2enzyme 3 X As D begins to increase, it inhibits enzyme 1 again and the cycle repeats itself.

31. Menu 31 The End