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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.