What is it??

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What is it??

• Enzymes are PROTEIN molecules.

• Protein molecules are composed of one or more amino acid chains, folded into uniquely shaped globs.

 Enzymes act as CATALYSTS!

 Catalysts are chemicals that regulate the rate of chemical reactions.

 Are not consumed or altered during the reaction

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Activation Energy

 Activation Energy is the energy input required to initiate any reaction.

 Enzymes regulate cell activities

(metabolism) by lowering the activation energy

 reactions, therefore, occur more rapidly and at

lower temperatures.

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Activation Energy

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Activation Energy

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Activation Energy

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Activation Energy ^animation

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Activation Energy

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FUNCTION vs. SHAPE

TWO THEORIES

1) LOCK & KEY THEORY

• Each chemical reaction requires its own enzyme therefore “one reaction = one enzyme” concept

• The enzyme forms a temporary bond with a special molecule called a SUBSTRATE

• A substrate is always…

– the substance acted upon

– the substance which is changing

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Enzyme

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Lock & Key (Cont’)

– The substrate(s) must fit into the particular 3-D structure of the enzyme’s ACTIVE SITE

– actual area of the enzyme that touches the substrate

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Get’in Together

• When the substrate and the enzyme

combine or “join” at the active site, the

tandem is called an Enzyme-Substrate

Complex.

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Lock & Key (Con’t)

– The ENZYME-SUBSTRATE COMPLEX then

separate into product(s) and enzyme

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Important

• Note that:

– The enzyme remains unchanged and ready to react

again with a new substrate.

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Important

• The substrate has been turned into products.

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Catalysts

• Chemicals that control the speed of reaction without altering the products formed

• Remains unchanged after reaction and can be used over and over

• Enzymes are PROTEIN catalysts that occur

in living things

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INDUCED FIT MODEL

• Improved Theory – 1973

– suggests that the shape of the active site does NOT exactly fit the shape of the substrate

– The substrate forces its way into the enzyme

– This makes for a tighter fit

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Induced Fit Model

– The orientation of the substrate molecules in the ENZYME- ENZYME-

SUBSTRATE COMPLEX

SUBSTRATE COMPLEX helps speed up the chemical reaction by

 adding stress to bonds more easily

 bringing reactive sites physically closer

together

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Induced Fit (Cont’d)

 Once a bond is formed (or broken) in substrate(s) then products are released and the ENZYME

REMAINS UNCHANGED and may be REUSED!

 A single enzyme can catalyze several million reactions in one minute

 The same enzyme may also catalyze the reverse

reaction

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Induced Fit Theory

 The net result is that a one step reaction is converted into a multi-step reaction,

therefore, lowering the activation energy –

the minimum amount of energy required to

initiate a chemical reaction.

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Naming Enzymes

 Enzymes are named after the substrate which it acts upon

 To name an enzyme, usually, the suffix “ase” is added to

 F or example:

Substrate Enzyme

Sucrose Sucrase Lactose Lactase

Peptide Bonds Peptidase

-Ketoglutarate ... ?????

-Ketoglutarase

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Factors Affecting Enzyme Reactions

• There are four factors that affect the rate at which an enzyme can work.

1) Temperature 2) pH

3) Substrate Concentration

4) Inhibitor Molecules

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Temperature

• In order for a reaction to occur, molecules must collide

– as temperature increases, collisions increase

Does the rate of reaction increase with

temperature??

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Temperature

Enzymes have an optimal

temperature at which the reaction is fastest.

Beyond or below this temperature, the rate of reaction decreases

This is because at high temperatures, the unique shape begins to change –

denaturation.

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Temperature and Denaturation

 This results in a loss of shape at the active site

 Each enzyme has its own optimal temperature

 Human body approx. = 37

C

 Sperm producing enzymes = 34

C

 This explains why fevers and colds are

dangerous (and shrinkage…)

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Temperature

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pH

Acidity or Alkalinity

– the lower the number the more acidic – the higher the number the more alkaline

Enzymes have an optimal pH at which the reaction is fastest

 Just like with temperature, pH’s out of the optimal range will cause a decrease in rate of reaction

 shape of active site changes = enzyme denatures

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pH

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Substrate Concentration

The more substrates you have, the greater the chance the enzyme will have of combining and reacting with it.

HOWEVER ...

 The rate does not continue to rise as you add more and more substrate.

 A substrate cannot join with the active site of an enzyme until it is free.

 Therefore, in an actual solution...

 once the number of substrate molecules exceeds the

number of enzyme reaction sites, the reaction rate

levels off.

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Substrate Concentration

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Inhibitor Molecules

 Inhibitor molecules interfere with the enzyme combining with its substrate.

– Competitive Inhibitor

 shaped like substrate

 COMPETES for active site

 fits into active site

= physically blocks substrate from entering active site

 enzyme becomes useless

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Competitive

Inhibition

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Inhibitor Molecules

 Examples:

 Cyanide – binds to enzyme in the

Electron Transport Chain preventing formation of ATP.

 Carbon Monoxide – binds to hemoglobin irreversibly, therefore, no oxygen can

be carried

 Penicillin – binds to enzyme that allows bacteria to make its protective

covering, therefore, bacteria becomes

susceptible to the immune system and

other drugs

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Inhibitor Molecules

Non-competitive Inhibitor

an inhibitor molecule binding to an enzyme (not to its active site) that causes a conformational change in its active site,

resulting in a decrease in activity.

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Non-competitive Inhibitor Molecules

Non-competitive Inhibitor

Enzyme

Substrates

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Non-competitive Inhibitor Molecules

 Examples:

Examples include Hg

, Ag

, Cu

and CN

inhibition of many enzymes (eg

cytochrome oxidase) by binding to -SH groups, thereby breaking -S-S- linkages

nerve gases like Sarin and DFP (diisopropyl fluorophosphate) inhibiting ethanoyl

(acetyl) cholinesterase. Inhibition.swf

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Inhibitor Molecules Animation

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Allostery

• is a form of non-competitive inhibition.

• the shape of allosteric enzymes can be altered by the binding of end products to an allosteric site, thereby decreasing its activity.

• Metabolites can act as allosteric inhibitors of enzymes earlier in a metabolic pathway and regulate metabolism according to the

requirements of organisms; a form of negative

feedback.

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• E.g. ATP inhibition of

phosphofructokinase in glycolysis and

inhibition of aspartate carbamoyltransferase

(ATCase) which catalyses the first step in

pyrimidine synthesis.

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Regulation of Enzyme Activity

 Some enzyme’s shape may be altered by a “moderator

molecule”.

 can be a cofactor (mineral)

 sometimes even the product

molecule.

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A Moderator Molecule

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Cofactors

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