1 Enzymes Enzymes Enzyme Action Factors Affecting Enzyme Action

2 Enzymes Catalysts for biological reactions Catalysts for biological reactions Most are proteins Most are proteins Lower the activation energy Lower the activation energy Increase the rate of reaction Increase the rate of reaction Activity lost if denatured Activity lost if denatured May be simple proteins May be simple proteins

3 Name of Enzymes End in –ase End in –ase Identifies a reacting substance Identifies a reacting substance sucrase – reacts sucrose lipase - reacts lipid Describes function of enzyme Describes function of enzyme oxidase – catalyzes oxidation hydrolase – catalyzes hydrolysis Common names of digestion enzymes still use –in Common names of digestion enzymes still use –in pepsin, trypsin

4 Enzyme Action: Lock and Key Model An enzyme binds a substrate in a region called the active site An enzyme binds a substrate in a region called the active site Only certain substrates can fit the active site Only certain substrates can fit the active site Amino acid R groups in the active site help substrate bind Amino acid R groups in the active site help substrate bind Enzyme-substrate complex forms Enzyme-substrate complex forms Substrate reacts to form product Substrate reacts to form product Product is released Product is released

5 Lock and Key Model E + S ES complex E + P E + S ES complex E + P S P P S

6 Enzyme Action: Induced Fit Model Enzyme structure flexible, not rigid Enzyme structure flexible, not rigid Enzyme and active site adjust shape to bind substrate Enzyme and active site adjust shape to bind substrate Increases range of substrate specificity Increases range of substrate specificity Shape changes also improve catalysis during reaction Shape changes also improve catalysis during reaction

7 Enzyme Action: Induced Fit Model E + S ES complex E + P S P P SS

8 Factors Affecting Enzyme Action: Temperature Little activity at low temperature Little activity at low temperature Rate increases with temperature Rate increases with temperature Most active at optimum temperatures (usually 37°C in humans) Most active at optimum temperatures (usually 37°C in humans) Activity lost with denaturation at high temperatures Activity lost with denaturation at high temperatures

9 Factors Affecting Enzyme Action Optimum temperature ReactionRate Low High Low High Temperature Temperature

10 Factors Affecting Enzyme Action: Substrate Concentration Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant) Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant) Maximum activity reached when all of enzyme combines with substrate Maximum activity reached when all of enzyme combines with substrate

11 Factors Affecting Enzyme Action Maximum activity ReactionRate substrate concentration substrate concentration

12 Factors Affecting Enzyme Action: pH Maximum activity at optimum pH Maximum activity at optimum pH Narrow range of activity Narrow range of activity Most lose activity in low or high pH Most lose activity in low or high pH

13 Factors Affecting Enzyme Action ReactionRate Optimum pH pH