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Lesson Objectives
Enzyme unit overview
± What are they?
± How they work
Activation energy
± What controls their activity
Rates of reaction
Substrate/enzyme concentrations
Temperature, pH
Enzyme inhibitors
± Practical to demonstrate ³Catalase´ activity in different tissue
samples
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Previous related topics covered?
Enzyme controlled reactions?
Proteins?
Lipase, protease, pectinase, amylase etc? ³Lock & Key´ molecular structures?
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By the end of the unit you should
be able to:- Explain enzymes as Gl obul ar Proteins which act
as catal ysts
Explain their catalytic action in terms of lowering
activation energy Describe examples of enzyme-catalysed
reactions
Discuss factors affecting reaction rates and
inhibition Describe how to investigate these effects
experimentally
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Enzymes:-
± Are defined as a BIOLOGICAL catalyst i.e. something that speeds up a
reaction. Up to 1012 fold
± Usually end in µ«ase¶.
± Discovered in 1900 in yeasts. Some 40,000 in human cells
± Control almost every metabolic reaction in living organisms
± Are globular proteins coiled into a very precise 3-dimentional shape with
hydrophilic side chains making them soluble
± Possess an active site such as a cleft in the molecule onto which other
substrate molecules can bind to form an enzyme-substrate compl ex
± Once the substrate has been either synthesised or split, enzymes can be re-
used.
± Do not µcreate¶ reactions
± Widely used in industrial cleaning
± Often require co-factors (co-enzymes) to function ± metal ions, or vitamin
derivatives
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Amylase + starch substrate
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How do enzymes work?
Reaction Mechanism
± In any chemical reaction a substrate isconverted into a product.
± In an enzyme catalysed reaction the substrate
first binds to the active site of the enzyme toform the enzyme-substrate complex
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Molecule Geometry
Substrate molecule fits into the enzyme
like a lock & key.
Enzyme shape distorts or it changes other factors to make the reaction happen
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³Activation Energy´
In a µnatural¶ reaction the product has a lower energy than the substrate so equilibrium will
take it in the direction of the product. However there is an energy µbarrier¶ to be
overcome
Enzymes lower the activation energy required to
bring about a reaction. EG catalase reduces the activation energy for
the reduction of H202 86-fold
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Reaction rate factors
Substrate
concentration
± Initially rate increases
with substrate conc.