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
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the reaction, the release
enzyme-substrate complex
product
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What about the other way?
substrate
enzyme-substrate complex
enzyme
product
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Lactase

• 1926 aas 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

• activation energy is the energy required to get a
  reaction going

activation energy
net energy change
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How do Enzymes work?

• They lower the activation energy of the reaction

• activation energy is the energy required to get a
  reaction going

activation energy
net energy change
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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

1. Measure S or P
2. Combine and Plot
Experiment with amount and rate
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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 because
• H-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 (lt4) (pepsin) while others work
best closer to a neutral pH (7)
pH for Optimum Activity Enzyme pH Optimum Lipase
(pancreas) 8.0 Lipase (stomach) 4.0 -
5.0 Lipase (castor oil) 4.7 Pepsin 1.5 -
1.6 Trypsin 7.8 - 8.7 Urease 7.0 Invertase
4.5 Maltase 6.1 - 6.8 Amylase (pancreas) 6.7
- 7.0 Amylase (malt) 4.6 - 5.2 Catalase 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