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Introduction to Enzymes
The Chemical Context of Life
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Objectives: Questions to be Answered:• What are enzymes?
• Why are they important?
• How do they work?
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What are enyzmes?
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4 Macro-moleculesof Biology
Enzymes
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4 Biomolecules / Macromoleculesof Biology
Proteins Carbohydrates Lipids Nucleic Acids
Enzymes
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4 Biomolecules / Macromoleculesof Biology
Proteins Carbohydrates Lipids Nucleic Acids
Enzymes
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Enzymes are Proteins
• Nearly all proteins are enzymes.
• Enzymes have a specific structure that determines its specific function.
• There are 20 amino acids that make up proteins.
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Why are they important?
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Chemical Reactions
• Chemical reactions that release energy often occur spontaneously (on their own).
• However, chemical reactions that absorb energy will not occur without a source of energy.
• A catalyst is a substance that speeds up the rate of a chemical reaction.
• Enzymes are biological catalysts.
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Biological Catalysts
• Enzymes change the rate of a chemical reaction without being used up or destroyed.
• They are essential to life in an organism because the rate of all cellular reactions is controlled by enzymes
• Enzymes are required for most chemical reactions that occur in biological organisms: Metabolism, digestion, etc.
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Real-Life Example
• Hydrogen peroxide (H2O2 ) is a by-product of cellular respiration.
• It must be removed from our cells to prevent damage.
• H2O2 breaks down into water (H2O) and oxygen (O2 ) naturally, but extremely slowly.
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• Catalase is an enzyme found in many cells but especially abundant in the liver.
• It is a particularly efficient enzyme, breaking down 500,000 hydrogen peroxide molecules per second.
• It drastically increases the speed of reaction.
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Cirrhosis of the Liver
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Reflection1. Of the four different macromolecules,
which one is almost always an enzyme?
2. What do enzymes do?
3. List one chemical reaction in living organisms that requires enzymes.
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How do they work?
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Activation Energy of Chemical Reactions
• For any reaction to occur, energy must be put into the reaction to start the breaking or making of new molecules.
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What are the two ways to increase the rate of reaction?
1. Add energy (difficult).
2. Decrease the activation energy by adding a catalyst or an enzyme (easy).
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Activation Energy
• For a reaction to occur, an energy barrier must be surmounted.
• Enzymes make the energy barrier smaller.
activation energywithout enzyme
activation energywith enzyme
energyreleased
by thereaction
products
starting substance
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Active Site• A substrate is the molecule that is to be changed in
a reaction.
• The crevice in an enzyme where the substrate binds to is called the active site.
• Enzymes have a specific active site for a specific substrate and a specific reaction.
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Animation: How Enzymes Work
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What else do you need to
know?
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Factors That Affect Enzyme Activity
• Temperature• pH
• Salt Concentration
• Temperature and pH can destroy the shape of an enzyme.
• When the shape is destroyed, so is the function. • When this happens, the enzyme is considered to
be denatured.
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Keys to Remember
• Enzymes speed up chemical reactions.
• Chemical Reactions of Life require enzymes.
• Without enzymes, life processes cannot occur.
(Cellular respiration, photosynthesis, protein synthesis, digestion, etc.)
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Reflection
1. What are the two ways to increase the rate of reaction?
2. What is a substrate?3. What is an active site?4. True or False. Enzymes have a specific
active site for a specific substrate and a specific reaction.
5. How might a defect in the structure of an enzyme lead to a possible health issue?