Enzymes

Characteristics All Enzymes are Proteins Catalysts – i.e. control the rate of a chemical reaction

How Enzymes work Enzymes bind and hold substrates (aka reactants) in a certain orientation to speed the chemical reaction along Enzymes change shape as they bind the substrates

the binding + substrates active site enzyme-substrate complex

the reaction, the release enzyme-substrate complex product

What about the other way? enzyme-substrate complex substrate enzyme product

Lactase 1926 aa’s long cell membranes - small intestines Lactase

Beano - alpha galactosidase breaks down trisaccharides raffinose – in beans, cabbage enzyme not in humans in bacteria in large intestines +

introducing activation energy net energy change activation energy –activation energy is the energy required to get a reaction going

How do Enzymes work? They lower the “activation energy” of the reaction net energy change –activation energy is the energy required to get a reaction going activation energy

Enzyme performance is affected by: – amount of substrate present –temperature –pH –Inhibitors –Poisons

Enzymes and Amount of Reactants  [ reactants ]  reaction rate because increased chance of finding molecules  [reactants]  reaction rate because decreased chance of finding molecules Experiment with amount and rate 1. Measure [S] or [P] 2. Combine and Plot

Enzymes and Temperature  temperature  reaction rate because increased kinetic energy breaks H-bonds  temperature  reaction rate because decreased kinetic energy does not break H-bonds

pH Acids – excess Hydrogen ions Bases – excess hydroxyl ions Neutral – equal numbers of H + and OH -

Enzymes and pH  pH changes reaction rate because H-bonds are altered  pH changes reaction rate because H-bonds are altered Experiment with pH and rate

Enzymes and pH each enzyme has an optimal pH; some work best in acidic conditions (<4) (pepsin) while others work best closer to a neutral pH (7) pH for Optimum Activity Enzyme pH Optimum Lipase (pancreas) 8.0 Lipase (stomach) Lipase (castor oil) 4.7 Pepsin Trypsin Urease 7.0 Invertase 4.5 Maltase Amylase (pancreas) Amylase (malt) Catalase 7.0

Enzymes and Inhibitors

bind to specific enzymes and decrease the reaction rate Normal substrate enzyme binding Competitive inhibitor binds to the active site Noncompetitive inhibitor binds to the enzyme and changes its shape

Competitive Inhibitors

Noncompetitive Inhibitors

Poisons - KCN Specific Irreversible Inhibitor of Cytochrome C Oxidase, ATP cannot be made Anaerobic respiration only Fatal build up - Lactic Acid

Poisons - Arsenic Nonspecific Inhibitor of cellular respiration enzymes Inhibits glucose break down Cell death results