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Enzymes
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Why Are Enzymes So Important?
Why are we devoting one whole lecture topic to a
protein molecule?– All chemical reactions in
living organisms require enzymes to work
Image: Jumping rope, Meagan E. Klein
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
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Chemical Reactions• A process that changes one set of
chemicals to another set of chemicals• Reactants – elements or compounds
that enter into a chemical reaction• Products – elements or compounds
produced by a chemical reaction
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Chemical Reactions
2H2 + O2 → 2H2O
reactants productsInvolves the breaking of bonds in the reactants and the formation of new
bonds in the product
Chemical equations – the symbols and numbers used to represent each element or substance in a chemical
reaction
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Energy in Reactions – Energy Changes
• Chemical reactions that release energy often occur spontaneously. –Ex. 2H2 + O2 → 2H2O
• Chemical reactions that absorb energy will not occur without a source of energy.–Ex. When water is changed into
hydrogen and oxygen gas
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Types of Reactions• Exothermic-When a reaction produces heat
• Endothermic-When a reaction requires heat to “get started”
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Energy in Reactions – Activation Energy
• Activation energy – energy needed to get a reaction started
http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20101/Bio%20101%20Lectures/energy/Image9.gif
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What Are Enzymes?• Most enzymes
are Proteins • Act as Catalyst to
accelerate a reaction
• Not permanently changed in the process
• Make materials needed by the cell
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Catalyst
• A substance that speeds up the rate of a chemical reaction by lowering the reaction’s activation energy
http://en.wikipedia.org/wiki/Image:Activation_energy.svg
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Enzymes• Are specific
for what they will catalyze
• End in –ase-Sucrase-Lactase-Maltase
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How do enzymes Work?
Enzymes work by weakening bonds which lowers activation energy
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Enzymes
FreeEnergy
Progress of the reaction
Reactants
Products
Free energy of activation
Without Enzyme
With Enzyme
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Enzyme-Substrate ComplexThe substance
(reactant) an enzyme acts on is the substrate
EnzymeSubstrate Joins
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Active Site• A active site of an enzyme
molecule binds to the substrate.
EnzymeSubstrate
Active Site
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enzyme
substrate
product
active site
Enzymes are not changed by the
reaction, they are reusable
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Active site of the enzyme
Two substrates
Enzyme
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The active site is like a lock
The substrates fit like a key in a lock
Enzyme
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The activation energy for these substrates to bind together has been lowered by the enzyme.
Enzyme
Chemical reaction!!!
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Basic Enzyme Diagram
Active site
The substrates have reacted and changed
into the product
Enzyme is unchanged
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Lock & Key model• Fit between the substrate and the
active site of the enzyme is exact • Like a key fits into a lock very
precisely• The key is analogous to the
enzyme and the substrate analogous to the lock.
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Induced Fit• A change in the shape of an enzyme’s active site
• Induced by the substrate
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Induced Fit Model• Enzymes can form to the shape
of its substrate.
http://en.wikipedia.org/wiki/File:Induced_fit_diagram.svg
Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College
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What Affects Enzyme Activity?
• Three factors:• Temperature
• pH• Inhibitors
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Temperature
- Effects rates of enzyme activity- Hot temps increase activity- Low temps reduce acitivity- High temps may denature
(unfold) the enzyme.
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pH • Effect on rates of enzyme activity
–Changes in pH changes protein shape~ Denatures
–Most human enzymes = pH 6-8•depends on where in body•pepsin (stomach) = pH 3
• trypsin (small intestines) = pH 8
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Two examples of Enzyme Inhibitors
a. Competitive inhibitors: are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site.
Enzyme
Competitive inhibitor
Substrate
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Inhibitors
b. Noncompetitive inhibitors:Inhibitors that do not enter
the active site, but bind to another part of the enzyme causing the enzyme to change its shape, which in turn alters the active site.
Enzyme
active site altered
NoncompetitiveInhibitor
Substrate
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Acids, Bases, and pH
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pH scale
– Measurement system that indicates the concentration of hydrogen (H+) ions in solution• A scale of 1-14 is used to describe
pH
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7 is considered neutral
Substances with a pH of 1-6 are considered acidic
Substances with a pH of 8-14 are considered basic or alkaline
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Acids and Bases • Acid – any substance that forms hydrogen
ions (H+) in water– Acidic solutions contain higher
concentrations of H+ ions and pH lower than 7.
• Base – any substance that forms hydroxide ions (OH-) in water– Basic, or alkaline, solutions contain lower
concentrations of H+ ions and pH higher than 7.
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Buffers - prevent sudden changes in pH. (used to maintain homeostasis)
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For Catalase Lab• EX for lab: Catalase is a common enzyme
found in nearly all living organisms exposed to oxygen (such as vegetables, fruit or animals). It catalyzes the decomposition of hydrogen peroxide to water and oxygen.
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