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1 21.1 Biological Catalysts 21.2 Names and Classification of Enzymes 21.3 Enzymes as Catalysts 21.4 Factors Affecting Enzyme Activity Chapter 21 Enzymes and Vitamins
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2 Enzymes are Biological Catalysts Enzymes are proteins that: Increase the rate of reaction by lowering the energy of activation. Catalyze nearly all the chemical reactions taking place in the cells of the body. Have unique three- dimensional shapes that fit the shapes of reactants.
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3 The name of an enzyme: Usually ends in –ase. Identifies the reacting substance. For example, sucrase catalyzes the reaction of sucrose. Describes the function of the enzyme. For example, oxidases catalyze oxidation. Could be a common name, particularly for the digestion enzymes such as pepsin and trypsin. Names of Enzymes
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4 Enzymes are classified according to the reaction they catalyze. ClassReactions catalyzed OxidoreductasesOxidation-reduction TransferasesTransfer groups of atoms Hydrolases Hydrolysis LyasesAdd atoms/remove atoms to/from a double bond IsomerasesRearrange atoms LigasesUse ATP to combine molecules Classification of Enzymes
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5 Classification of Enzymes: Oxidoreductases and Transferases
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6 Classification: Hydrolases and Lyases
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7 Classification: Isomerases and Ligases
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8 The active site: Is a region within an enzyme that fits the shape of molecules called substrates. Contains amino acid R groups that align and bind the substrate. Releases products when the reaction is complete. Active Site
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9 Enzymes may recognize and catalyze: A single substrate. A group of similar substrates. A particular type of bond. Enzyme Specificity
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10 Lock-and-Key Model In the lock-and-key model of enzyme action: The active site has a rigid shape. Only substrates with the matching shape can fit. The substrate is a key that fits the lock of the active site.
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11 Induced-fit Model In the induced-fit model of enzyme action: The active site is flexible, not rigid. The shapes of the enzyme, active site, and substrate adjust to maximum the fit, which improves catalysis. There is a greater range of substrate specificity.
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12 Enzyme Catalyzed Reaction The proper fit of a substrate (S) in an active site forms an enzyme-substrate (ES) complex. E + S ES Within the ES complex, the reaction occurs to convert substrate to product (P). ES E + P The products, which are no longer attracted to the active site, are released. Overall, substrate is convert to product. E + S ES E + P
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13 Example of An Enzyme Catalyzed Reaction
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14 Diagnostic Enzymes The levels of diagnostic enzymes determine the amount of damage in tissues.
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15 Isoenzymes Isoenzymes catalyze the same reaction in different tissues in the body. Lactate dehydrogenase, which converts lactate to pyruvate, (LDH) consists of five isoenzymes.
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16 Enzymes: Are most active at an optimum temperature (usually 37°C in humans). Show little activity at low temperatures. Lose activity at high temperatures as denaturation occurs. Temperature and Enzyme Action
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17 Enzymes: Are most active at optimum pH. Contain R groups of amino acids with proper charges at optimum pH. Lose activity in low or high pH as tertiary structure is disrupted. pH and Enzyme Action
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18 Optimum pH Values Most enzymes of the body have an optimum pH of about 7.4. In certain organs, enzymes operate at lower and higher optimum pH values.
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19 Enzyme Concentration The rate of reaction increases as enzyme concentration increases (at constant substrate concentration). At higher enzyme concentrations, more substrate binds with enzyme.
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20 Substrate Concentration The rate of reaction increases as substrate concentration increases (at constant enzyme concentration). Maximum activity occurs when the enzyme is saturated.
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