Enzymes

What are they?

Organic/Biological CatalystsProteinsReusableThere’s over 40,000 found in humansUsually end in the suffix –aseNamed after what it “eats” (ex: if an enzyme is meant to eat lactose the enzyme is lactase)

How do they work?

Enzymes possess an active site (which is like a cleft in the molecule)The active site is where its food (substrate) goes intoWhen the substrate binds to the enzyme it is called an enzyme substrate complex

A new substrate will then be synthesized (created) or the old one will be splitEnzymes DO NOT change in the process

Reactions

Enzymes CANNOT create reactions they only speed them up

Enzymes speed up reactions by lowering the activation energy (energy needed to get the reaction to take place)There are two parts to a chemical reaction: reactants (what goes in) and products (what comes out)Example: Carbonic anhydrase is an enzyme found in RBCs where it catalyzes the reaction CO2 + H2O ↔ H+ + HCO3

− this allows blood to transport CO2 from the tissues to the lungs (one molecule of this enzyme can process one million molecules of CO2 each second

Synthesis Reaction

Active site

Properties

Specific

Increase rate of the reaction

Unchanged at the end of the reaction

Need themReactions too slow to maintain life

Can’t increase temperatures/pressure in cells (fatal)

Enzymes

Molecule GeometrySubstrate molecule fits into the enzyme like a lock & key.Enzyme shape distorts or changes other factors to make the reaction happenHowever certain substances canbind to the enzyme at sites other than the active site and modify its activity (inhibitors/co-factors)Idea that the enzyme is flexible (induced fit)

Activation Energy

In a ‘natural’ 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 ‘barrier’ to be overcomeEnzymes lower the activation energy required to bring about a reaction.Activation energy- the minimum amount of energy needed to start a reaction

Energy

Progress of reaction

Substrates Products

High energy intermediate

Activation energy

Enzyme activity

Four Variables

Temperature

pH

Enzyme Concentration

Substrate Concentration

Optimum ConditionEnzymes function best or are most active in specific

conditions known as optimum

conditions.

Rat

e of

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Temperature

0 20 30 5010 40 60

40oC - denatures

5- 40oC Increase in Activity

<5oC - inactive

Rat

e of

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ctio

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pH

1 3 42 5 6 7 8 9

Narrow pH optima

Disrupt Ionic bonds - Structure

Effect charged residues at activesite

Rat

e of

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ctio

n

Enzyme Concentration

Enzyme Concentration

Rat

e of

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Substrate Concentration

Substrate Concentration

Active sites full- maximum turnover