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Enzymes

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What are Enzymes?

• 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

Enzyme

Substrate

Enzyme / Substrate Complex

Enzyme unchanged

Products

Active site

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Enzyme Action

• Active site is sometimes flexible

• When substrate(s) enter active site enzyme changes shape

• Induced Fit Theory

Enzyme

Substrates

Active site Enzyme / Substrate

ComplexEnzyme unchanged

Product

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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