Enzymes
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What are Enzymes?
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Globular proteins
Biological catalysts
Do not change after reaction
They are found in small quantities
Specific
Reactions are reversible
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How Enzymes Work
• Enzymes lower the energy required for a
chemical reaction to occur (activation
energy)
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How Enzymes Work
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Enzyme Structure
• Tertiary Structure of enzyme determines
its unique shape.
• Forms its ACTIVE SITE
Active Site
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Enzyme Action
• Enzymes work on specific substrates
• Substrate(s) has to fit in the active site
• Lock and key hypothesis
Substrate
Products
Active site
Enzyme
Enzyme / Substrate
Complex
Enzyme unchanged
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Enzyme Action
• Active site is sometimes flexible
• When substrate(s) enter active site enzyme
changes shape
• Induced Fit Theory
Product
Substrates
Active site
Enzyme
Enzyme / Substrate
Complex
Enzyme unchanged
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Enzyme Action
• Rate of an enzyme reaction can be
affected by:
– Temperature
– pH
– Enzyme Concentration
– Substrate Concentration
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Monitoring Enzyme Action
• In an experiment enzyme action can be
timed by:
Formation of
Products e.g. gas
Disappearance of
Substrate e.g. starch
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Enzyme Activity and
Temperature
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Enzyme Activity and pH
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Enzyme Activity and Substrate
Concentration
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Enzyme Activity and Enzyme
Concentration
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What to do now
• Read Key Biological Principle box page
77-79
• Answer Checkpoints 2.3 and 2.4
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