2 Program Objectives List 6 common features of enzyme action. Describe the role of the active site. Draw an energy diagram and identify the substrates, products, activated complex and activation energy. Describe and explain the sensitivity of enzymes to heat and pH. Identify mechanisms by which an enzyme may reduce the activation energy for a reaction.
3 Enzymes are the working unit of an organism. Every chemical reaction that occurs in an organism is made possible by a specific enzyme. Enzymes A cup of sugar left undisturbed for twenty years changes very little. However when you eat sugar, it rapidly undergoes chemical change. Enzymes account for the differences in the rate of change
4 Enzymes Catalysts for biological reactions Most are proteins Lower the activation energy Increase the rate of reaction Activity lost if denatured May be simple proteins May contain cofactors such as metal ions or organic (vitamins)
6 Energy of Activation is necessary to convert the molecule to its products. Potential Energy
7 Enzymes lower activation energy increasing the rate of the reaction.
8 Ways enzymes speed reactions *increase the frequency of successful collisions *improve the orientation between colliding substrates *provide a new reaction path with a lower activation energy –Warp and weaken a bond –Provide a favorable electronic environment weakening bond
9 Enzymes are sensitive to environmental change. –temperature changes shape of active site –pH changes shape of active site –enzyme concentration –substrate concentration –inhibitors
10 Cofactors: An ion or molecule that must be associated with an enzyme for the enzyme’s proper functioning. Several large organic molecules, called coenzymes, serve as cofactors. FAD, NAD & NADP, are examples.
11 Name of Enzymes End in –ase Identifies a reacting substance sucrase – reacts sucrose lipase - reacts lipid Describes function of enzyme oxidase – catalyzes oxidation hydrolase – catalyzes hydrolysis Common names of digestion enzymes still use –in pepsin, trypsin
12 Learning Check E1 Match the type of reaction with the enzymes: (1) aminase(2) dehydrogenase (3) Isomerase(4) synthetase A.Converts a cis-fatty acid to trans. B.Removes 2 H atoms to form double bond C.Combine two molecules using ATP D.Adds NH 3
13 Enzyme Action: Lock and Key Model An enzyme binds a substrate in a region called the active site Only certain substrates can fit the active site Amino acid R groups in the active site help substrate bind Enzyme-substrate complex forms Substrate reacts to form product Product is released
15 Lock and Key Model + + E + S ES complex E + P S P P S
16 Enzyme Action: Induced Fit Model Enzyme structure flexible, not rigid Enzyme and active site adjust shape to bind substrate Increases range of substrate specificity Shape changes also improve catalysis during reaction
17 The binding of the substrate to the enzyme alters the structure of the enzyme, placing some strain on the substrate and further facilitating the reaction
18 Enzyme Action: Induced Fit Model E + S ES complex E + P S P P SS
19 Learning Check E2 A.The active site is (1) the enzyme (2) a section of the enzyme (3) the substrate B. In the induced fit model, the shape of the enzyme when substrate binds (1) Stays the same (2) adapts to the shape of the substrate
20 Solution E2 A.The active site is (2) a section of the enzyme B. In the induced fit model, the shape of the enzyme when substrate binds (2) adapts to the shape of the substrate
21 Factors Affecting Enzyme Action: Temperature Little activity at low temperature Rate increases with temperature Most active at optimum temperatures (usually 37°C in humans) Activity lost with denaturation at high temperatures
22 Factors Affecting Enzyme Action Optimum temperature Reaction Rate Low High Temperature
23 Factors Affecting Enzyme Action: Substrate Concentration Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant) Maximum activity reached when all of enzyme combines with substrate
25 Factors Affecting Enzyme Action: pH Maximum activity at optimum pH R groups of amino acids have proper charge Tertiary structure of enzyme is correct Narrow range of activity Most lose activity in low or high pH
27 Learning Check E3 Sucrase has an optimum temperature of 37°C and an optimum pH of 6.2. Determine the effect of the following on its rate of reaction (1) no change (2) increase (3) decrease A. Increasing the concentration of sucrose B. Changing the pH to 4 C. Running the reaction at 70°C
28 Solution E3 Sucrase has an optimum temperature of 37°C and an optimum pH of 6.2. Determine the effect of the following on its rate of reaction (1) no change (2) increase (3) decrease A. 2, 1 Increasing the concentration of sucrose B. 3 Changing the pH to 4 C. 3 Running the reaction at 70°C
29 Enzyme Inhibition Inhibitors cause a loss of catalytic activity Change the protein structure of an enzyme May be competitive or noncompetitive Some effects are irreversible
30 Competitive Inhibition A competitive inhibitor Has a structure similar to substrate Occupies active site Competes with substrate for active site Has effect reversed by increasing substrate concentration
31 Noncompetitive Inhibition A noncompetitive inhibitor Does not have a structure like substrate Binds to the enzyme but not active site Changes the shape of enzyme and active site Substrate cannot fit altered active site No reaction occurs Effect is not reversed by adding substrate
34 Learning Check E4 Identify each statement as describing an inhibitor that is (1) Competitive (2) Noncompetitive A. Increasing substrate reverses inhibition B. Binds to enzyme, not active site C. Structure is similar to substrate D. Inhibition is not reversed with substrate
35 Solution E4 Identify each statement as describing an inhibitor that is (1) Competitive (2) Noncompetitive A. 1 Increasing substrate reverses inhibition B. 2 Binds to enzyme, not active site C. 1 Structure is similar to substrate D. 2 Inhibition is not reversed with substrate
36 Active Site Summary *is usually a crevice or pocket on the protein *formed with only a few of the enzymes amino acids *changes its shape in response to the substrate
37 The active site is a region where an enzyme molecule is folded in the shape of a crevice or cleft and where a particular reaction is catalyzed
38 The substrate is a specific molecules that an enzyme can chemically recognize, bind to briefly, and modify in a specific way.
39 Enzymes are specific – only catalyzes one reaction Active site is complementary shape to the substrate affected.
40 Reaction Specificity An enzyme always puts out the same kind of product when fed a given substrate.
41 Enzymes perform simple reactions. isomerization – rearrangement of molecules exchange – transfer of atoms addition – put two substrates together decomposition – change substrate into two products.
42 Things enzymes do NOT do. *Enzymes don’t make anything happen that would not eventually happen on its own, They just make it happen faster -- at least a million times faster, usually. *Enzymes do NOT initiate the reaction. *Enzymes do NOT Provide energy. –LIGHT provides activation energy –OR INETIC ENERGY is the activation energy.
43 *Enzymes are not used up in a chemical reaction. *Enzymes do have a working lifetime and eventually do break down. *Enzymes are not permanently altered in a reaction.
44 7. The enzyme is NOT changed in the reaction.