1. Enzymes and Substrates Presenter: Mrs. Knopke FUHS Science Dept.

2. Laws of Thermodynamics 1 st law – Energy cannot be created or Destroyed. 1 st law – Energy cannot be created or Destroyed. - it can be converted form one form to another. The sum of the energy id equal to the sum of the energy after the conversion - it can be converted form one form to another. The sum of the energy id equal to the sum of the energy after the conversion 2 nd Law – Some usable energy dissipates during transformation and is lost. Usually as heat, the amount of usable energy therefore decreases. 2 nd Law – Some usable energy dissipates during transformation and is lost. Usually as heat, the amount of usable energy therefore decreases.

3. Catabolic and Anabolic Reactions The energy-related reactions within the cells generally involve the synthesis or the brekdown of complex organic compounds The energy-related reactions within the cells generally involve the synthesis or the brekdown of complex organic compounds ATP produced in catabolic reactions provide the energy for Anabolic reactions. Anabolic and Catabolic reactions are therefore coupled. ATP produced in catabolic reactions provide the energy for Anabolic reactions. Anabolic and Catabolic reactions are therefore coupled.

4. Anabolic Reactions Anabolic reactions are those that synthesize compounds. Energy is required for these reactions. Anabolic reactions are those that synthesize compounds. Energy is required for these reactions. Atoms and molecules + Energy = larger molecule Atoms and molecules + Energy = larger molecule Energy

5. Catabolic Reactions Reactions that break down molecules are called catabolic reactions. Energy is released when molecules are broken down. Reactions that break down molecules are called catabolic reactions. Energy is released when molecules are broken down. Energy

6. Coupled reactions

7. Anabolic Reactions consume energy

8. Catabolic Reactions Release Energy

9. Activation Energy In either kind of reaction additional energy must be supplied to start the reaction. This energy is Activation Energy

10. What are enmzymes? Substances that speed up chemical reactions are called Catalysts. Organic catalysts are called Enzymes. Substances that speed up chemical reactions are called Catalysts. Organic catalysts are called Enzymes. Enzymes are specific for one particular reaction of group of related reactions. Enzymes are specific for one particular reaction of group of related reactions. Many reactions cannot occur without the correct enzyme Many reactions cannot occur without the correct enzyme Often named by adding an - ase Often named by adding an - ase

11. Induced-Fit Theory An enzyme-substrate complex forms when the enzymes active site binds with the substrate like a key fitting a lock. An enzyme-substrate complex forms when the enzymes active site binds with the substrate like a key fitting a lock. The shape of the enzyme must match the shape of the substrate. Enzymes are therefore very specific; they will only function correctly if the shape of the substrate matches the active site. The shape of the enzyme must match the shape of the substrate. Enzymes are therefore very specific; they will only function correctly if the shape of the substrate matches the active site.

15. Enzymes are substrate specific A substrate is a reactant which binds to an enzyme. A substrate is a reactant which binds to an enzyme. When a substrate or substrates binds to an enzyme, the enzyme catalyzes the conversion of the substrate to the product. When a substrate or substrates binds to an enzyme, the enzyme catalyzes the conversion of the substrate to the product. –Sucrase is an enzyme that binds to sucrose and breaks the disaccharide into fructose and glucose.

17. The active site of an enzymes is typically a pocket or groove on the surface of the protein into which the substrate fits. The specificity of an enzyme is due to the fit between the active site and that of the substrate. As the substrate binds, the enzyme changes shape leading to a tighter induced fit, bringing chemical groups in position to catalyze the reaction.

18. The substrate molecule normally does not fit exactly in the active site. This induces a change in the enzymes conformation (shape) to make a closer fit. The substrate molecule normally does not fit exactly in the active site. This induces a change in the enzymes conformation (shape) to make a closer fit. In reactions that involve breaking bonds, the inexact fit puts stress on certain bonds of the substrate. This lowers the amount of energy needed to break them. In reactions that involve breaking bonds, the inexact fit puts stress on certain bonds of the substrate. This lowers the amount of energy needed to break them.

19. The enzyme does not form a chemical bond with the substrate. After the reaction, the products are released and the enzyme returns to its normal shape. The enzyme does not form a chemical bond with the substrate. After the reaction, the products are released and the enzyme returns to its normal shape. Because the enzyme does not form chemical bonds with the substrate, it remains unchanged. As a result, the enzyme molecule can be reused. Only a small amount of enzyme is needed because they can be used repeatedly. Because the enzyme does not form chemical bonds with the substrate, it remains unchanged. As a result, the enzyme molecule can be reused. Only a small amount of enzyme is needed because they can be used repeatedly.

20. Activation Energy and Enzymes The amount of activation energy that is required is considerably less when enzyme is present. The amount of activation energy that is required is considerably less when enzyme is present.activation energyactivation energy

21. Conditions that Affect Enzymatic Reactions Rate of Reaction 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. 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. Fast enzymes catalyze up to 500,000 molecules per second. Substrate concentration, enzyme concentration, Temperature, and pH affect the rate of enzyme reactions. Substrate concentration, enzyme concentration, Temperature, and pH affect the rate of enzyme reactions.

22. 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. 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.

23. Substrate Concentration 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. 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.

24. Enzyme Concentration If there is insufficient enzyme present, the reaction will not proceed as fast as it otherwise would because all of the active sites are occupied with the reaction. Additional active sites could speed up the reaction. If there is insufficient enzyme present, the reaction will not proceed as fast as it otherwise would because all of the active sites are occupied with the reaction. Additional active sites could speed up the reaction.

25. 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. 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.

26. Enzyme Concentration 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. 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.

27. Temperature effect on enzymes Higher temperature generally causes more collisions among the molecules and therefore increases the rate of a reaction. More collisions increase the likelihood that substrate will collide with the active site of the enzyme, thus increasing the rate of an enzyme-catalyzed reaction. Higher temperature generally causes more collisions among the molecules and therefore increases the rate of a reaction. More collisions increase the likelihood that substrate will collide with the active site of the enzyme, thus increasing the rate of an enzyme-catalyzed reaction.

28. Temperature Above a certain temperature, activity begins to decline because the enzyme begins to denature. Above a certain temperature, activity begins to decline because the enzyme begins to denature.denature The rate of chemical reactions therefore increases with temperature but then decreases. The rate of chemical reactions therefore increases with temperature but then decreases.

30. 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. 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.R groupsR groups

31. pH The diagram below 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, and therefore, its optimum pH is in the neutral range to match the pH of the duodenum The diagram below 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, and therefore, its optimum pH is in the neutral range to match the pH of the duodenumpepsinstomachTrypsin duodenumpepsinstomachTrypsin duodenum

32. Metabolic Pathways Metabolism refers to the chemical reactions that occur within cells. A hypothetical metabolic pathway is shown below. Metabolism refers to the chemical reactions that occur within cells. A hypothetical metabolic pathway is shown below. Reactions occur in a sequence and a specific enzyme catalyzes each step. Intermediates can be used as starting points for other pathways. For example, "C" in the diagram above can be used to produce "D" but can also be used to produce "F".

33. Cyclic Pathways Some metabolic pathways are cyclic. The function of the cyclic pathway below is to produce E from A. Several intermediate steps are involved in the production of E. Some metabolic pathways are cyclic. The function of the cyclic pathway below is to produce E from A. Several intermediate steps are involved in the production of E.

35. Regulation of Enzyme Activity Cells have built-in control mechanisms to regulate enzyme concentration and activity. Cells have built-in control mechanisms to regulate enzyme concentration and activity.

36. Regulation of Protein Synthesis (Genetic Regulation) Enzymes are proteins. You can regulate them by making more or less of them as needed. The topic of regulating protein synthesis is deferred to a later chapter. Enzymes are proteins. You can regulate them by making more or less of them as needed. The topic of regulating protein synthesis is deferred to a later chapter.protein synthesisprotein synthesis

37. Regulation of Enzymes Already Produced Competitive Inhibition Competitive Inhibition In competitive inhibition, a similar- shaped molecule competes with the substrate for active sites. In competitive inhibition, a similar- shaped molecule competes with the substrate for active sites.active sitesactive sites

38. Binding by some molecules, inhibitors, prevent enzymes from catalyzing reactions. Binding by some molecules, inhibitors, prevent enzymes from catalyzing reactions. –If binding involves covalent bonds, then inhibition is often irreversible. –If binding is weak, inhibition may be reversible. If the inhibitor binds to the same site as the substrate, then it blocks substrate binding via competitive inhibition. If the inhibitor binds to the same site as the substrate, then it blocks substrate binding via competitive inhibition. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 6.17a, b

39. 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. 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.

40. Binding by the inhibitor causes the enzyme to change shape, rendering the active site unreceptive at worst or less effective at catalyzing the reaction. Binding by the inhibitor causes the enzyme to change shape, rendering the active site unreceptive at worst or less effective at catalyzing the reaction. Reversible inhibition of enzymes is a natural part of the regulation of metabolism. Reversible inhibition of enzymes is a natural part of the regulation of metabolism. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 6.17c

41. Most allosterically regulated enzymes are constructed of two or more polypeptide chains. Most allosterically regulated enzymes are constructed of two or more polypeptide chains. Each subunit has its own active site and allosteric sites are often located where subunits join. Each subunit has its own active site and allosteric sites are often located where subunits join. The whole protein oscillates between two conformational shapes, one active, one inactive. The whole protein oscillates between two conformational shapes, one active, one inactive. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 6.18a

42. Some allosteric regulators, activators, stabilize the conformation that has a functional active site. Some allosteric regulators, activators, stabilize the conformation that has a functional active site. Other regulators, inhibitors, stabilize the conformation that lacks an active site. Other regulators, inhibitors, stabilize the conformation that lacks an active site. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 6.18b

43. In enzymes with multiple catalytic subunits, binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits, a process called cooperativity. In enzymes with multiple catalytic subunits, binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits, a process called cooperativity. This mechanism amplifies the response of enzymes to substrates, priming the enzyme to accept additional substrates This mechanism amplifies the response of enzymes to substrates, priming the enzyme to accept additional substrates Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 6.20

44. Noncompetitive Inhibition 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. 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. 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. 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.

45. Feedback Inhibition Negative feedback inhibition is like a thermostat. When it is cold, the thermostat turns on a heater which produces heat. Heat causes the thermostat to turn off the heater. Heat has a negative effect on the thermostat; it feeds back to an earlier stage in the control sequence as diagrammed below. Negative feedback inhibition is like a thermostat. When it is cold, the thermostat turns on a heater which produces heat. Heat causes the thermostat to turn off the heater. Heat has a negative effect on the thermostat; it feeds back to an earlier stage in the control sequence as diagrammed below.

46. Feedback Inhibition Many enzymatic pathways are regulated by feedback inhibition. As an enzyme's product accumulates, it turns off the enzyme just as heat causes a thermostat to turn off the production of heat. The end product of the pathway binds to an allosteric site on the first enzyme in the pathway and shuts down the entire sequence. Many enzymatic pathways are regulated by feedback inhibition. As an enzyme's product accumulates, it turns off the enzyme just as heat causes a thermostat to turn off the production of heat. The end product of the pathway binds to an allosteric site on the first enzyme in the pathway and shuts down the entire sequence.

47. Feedback inhibition Feedback inhibition occurs in most cells.

48. One of the common methods of metabolic control is feedback inhibition in which a metabolic pathway is turned off by its end product. One of the common methods of metabolic control is feedback inhibition in which a metabolic pathway is turned off by its end product. The end product acts as an inhibitor of an enzyme in the pathway. The end product acts as an inhibitor of an enzyme in the pathway. When the product is abundant the pathway is turned off, when rare the pathway is active. When the product is abundant the pathway is turned off, when rare the pathway is active. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 6.19

49. Function of Coenzymes: Many enzymes require nonprotein helpers, cofactors, for catalytic activity. Many enzymes require nonprotein helpers, cofactors, for catalytic activity. –They bind permanently to the enzyme or reversibly. –Some inorganic cofactors include zinc, iron, and copper. Organic cofactors, coenzymes, include vitamins or molecules derived from vitamins. Organic cofactors, coenzymes, include vitamins or molecules derived from vitamins. The manners by which cofactors assist catalysis are diverse. The manners by which cofactors assist catalysis are diverse.