Download - Enzymes
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Enzymes
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Characteristics
• All Enzymes are Proteins• Catalysts – i.e. control the rate of a
chemical reaction
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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
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the binding
+
substrates
active site enzyme-substrate complex
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the reaction, the release
enzyme-substrate complex
product
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What about the other way?
enzyme-substrate complexsubstrate
enzyme
product
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Lactase
• 1926 aa’s long• cell membranes - small intestines
Lactase
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Beano - alpha galactosidase
• breaks down trisaccharides•raffinose – in beans, cabbage
• enzyme • not in humans• in bacteria in large intestines
+
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another example – glyceraldehyde-3-dehydrogenase
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re-introducing activation energy
net energy change
acti
vati
on
en
erg
y
–activation energy is the energy required to get a reaction going
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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
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How do they do it?• They lower the “activation energy” of the reaction
net energy change
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Enzyme performance is affected by:
– amount of substrate present– temperature– pH– Inhibitors– Poisons
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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
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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
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pH
• Acids – excess Hydrogen ions• Bases – excess hydroxyl ions• Neutral – equal numbers of H+
and OH-
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Enzymes and pH
pH changes reaction rate becauseH-bonds are altered
pH changes reaction rate because H-bonds are altered
Experiment with pH and rate
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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) 8.0Lipase (stomach) 4.0 - 5.0Lipase (castor oil) 4.7Pepsin 1.5 - 1.6Trypsin 7.8 - 8.7Urease 7.0Invertase 4.5Maltase 6.1 - 6.8Amylase (pancreas) 6.7 - 7.0Amylase (malt) 4.6 - 5.2Catalase 7.0
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Enzymes and Inhibitors
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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
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Competitive Inhibitors
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Noncompetitive Inhibitors
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Poisons - KCN
• Specific Irreversible Inhibitor of Cytochrome C Oxidase,
• ATP cannot be made
• Anaerobic respiration only
• Fatal build up - Lactic Acid
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Poisons - Arsenic• Nonspecific Inhibitor of cellular respiration enzymes
• Inhibits glucose break down
• Cell death results