Topic ThreeTopic ThreeEnzymesEnzymes

Catalysts and EnzymesCatalysts and EnzymesWhy are enzymes important? • hundreds of chemical

reactions are in progress in a typical living cell at a given moment

• These reactions provide energy and substances needed for growth and repair

• Chemical reactions would not be possible without ENZYMES

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CatalystsCatalysts

Catalyst = a chemical that speeds up the rate of a chemical reaction•Is not used up in the reaction

Watch a catalyst in action!

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EnzymesEnzymesEnzyme = an organic catalyst•Made up of proteins•Allow chemical reactions to happen at room temperature•Speed up reactions without increasing temperature!

Enzymes are everywhere!

In saliva…

… stomach

… even mitochondria!

Draw the picture below to show how an enzyme works:

Substrate

Enzyme

Active Sites

Enzyme-Substrate Complex

Products

What type of reaction is this?

Hydrolysis or catabolic reaction.

• Chemical reactions normally occur very SLOWLY!

• Increasing temperature increases the rate of reaction

• But increasing temperature too much will denature proteins and damage our cells!

• Enzymes speed up the rate of a reaction without increasing the temperature

Why are enzymes necessary?

• Chemical reactions require an initial energy input to start

• Ex: Rock must be rolled up the hill before it is able to roll down the other side of the hill by itself

• Activation Energy = energy required to initiate (start) a chemical reaction

Activation EnergyActivation Energy

Activation EnergyActivation EnergyNo enzyme = higher activation energy

With enzyme =

lower activation energy

Enzymes do not change the amount

of energy available!

3-2 Enzymes are Substrate Specific3-2 Enzymes are Substrate Specific

• Substrate: a molecule which attaches to the active site of an enzyme

• Active site: Area of an enzyme that combines with a substrate molecule

• Each enzyme is specific for a particular substrate– - Like lock and key

Substrates

Active Site

Naming of enzymesNaming of enzymes• Enzymes are given unique names based on the specific substrates • Enzyme name = name of the substrate + ASE

Fructose + GlucoseSucrose + H2OSucrase

SubstrateSubstrate EnzymeEnzymeMaltoseMaltose

LactoseLactose

ProteinProtein

Starch Starch

LipidsLipids

Polypeptides Polypeptides

Naming Enzymes:Fill in the following table!!

Maltase

LactaseProtease

Amylase

Lipase

Peptidase

Not all enzymes end with “ase”!! Pepsin

and Trypsin are protein enzymesthat do not end

in “ase”

stomach

Not all enzymes end with “ase”!! Pepsin and Trypsin are protein enzymes that do not end in “ase.”

pancreas

3-3 Basic Mechanism of Enzyme Action

• Chemical reactions occur when molecules collide or bonds are broken

• Enzymes increase the probability of reactions occurring inside cells by bringing substrate molecules CLOSER together

• Enzymes can form bonds between molecules or break bonds

Lock and Key HypothesisLock and Key Hypothesis

• The active site of the enzymes fits the substrate molecules• This forms an enzyme substrate complex

and

Product

Enzyme – Lock and Key HypothesisEnzyme – Lock and Key Hypothesis

A

B

C

D B

E

A: substratesB: enzymeC: active siteD: enzyme-substrate complexE: productsF: enzyme to be used again

F

3-4 Coenzymes and Cofactors3-4 Coenzymes and Cofactors• Recall:

– Cofactors are inorganic molecules– Examples: iron, zinc, calcium, magnesium and

potassium– Coenzymes are organic molecules such as

vitamins

Enzymes may not act alone...Enzymes may not act alone...• Sometimes additional chemicals are necessary

ingredients to permit enzyme activity• Enzyme co-factors and co-enzymes are often linked with

enzyme activity• Coenzymes and cofactors change the shape of the active

site on the enzyme!• Where a co-enzyme is lacking, enzyme activity may be

reduced

Enzyme Action Enzyme Action

1. Enzyme

2. Co-enzyme3. Substrate 4. Products

• What happens when someone has a poor diet???– The chemical reactions requiring coenzymes

(vitamins) and cofactors (minerals) cannot work when someone has a poor diet!!

Coenzymes and CofactorsCoenzymes and Cofactors

Other factors affecting Enzyme Activity a) Temperature

• Enzymes have an optimum temperature where the greatest number of molecular collisions occurs

• An increase in temperature causes an increase in reaction rate– More molecules = more collisions

• Optimum temperature range of most human enzymes is 35-40oC

• Examples of optimum temperatures: – Hot springs bacteria = 85oC– Antarctic ice fish = 2oC

Temperature cont…Temperature cont…• High temperatures cause enzymes

to denature (change shape)– Why do you think high fevers for long

periods of time are dangerous?

Reaction rate

Temperature

Optimal temperature = highest rate of chemical

reactions

Enzyme denatures

37oC

Effects of pHEffects of pH• Optimal pH for most enzymes is pH 6-8 but some operate

at more extremes– The enzyme pepsin has a optimal pH of 2

• A pH above or below the optimal pH may cause denaturation– Enzyme activity will lower because the shape of the enzyme has

changed…

Effects of pHEffects of pH

Substrate ConcentrationSubstrate Concentration• As substrate concentration increases, enzyme activity increases • As enzyme active sites become full, if the number of substrate

molecules exceed the number of enzymes molecules, then the reaction levels off.

Reaction rate

Substrate concentration

No more enzymes available = reaction rate leveling off

More substrate for the enzyme

to use = increasing reaction rate

Competitive Inhibitors• Inhibitors have shapes very similar

to the substrate and also bind to the active site of the enzyme

• When an inhibitor combines with the enzyme it prevents it from functioning properly• Inhibitor must be removed for

normal functioning to occur• decreases enzyme activity by

filling the active site so substrates cannot join!

Examples of competitive inhibitors include carbon monoxide, cyanide and penicillin

Carbon Monoxide (CO)Carbon Monoxide (CO)

• Many poisons and drugs act as competitive inhibitors…

• CO for example competes with oxygen for the active site on the hemoglobin molecule. – In fact, it binds to

hemoglobin 200X faster than oxygen! Once CO fits itself in, it rarely is dislodged

CyanideCyanide• Cyanide attaches to enzyme in mitochondria,

preventing the breakdown of sugars for energy. Cell dies!!

• Without the energy needed for active transport, protein synthesis, transport of nutrients, and elimination of wastes, a cell dies almost instantly!

PenicillinPenicillin• Penicillin kills invading

bacteria• Blocks an enzyme necessary

for the synthesis of protective walls in bacteria

• No effect on human enzymes

Topic 3-6: Control of Enzyme ActivityTopic 3-6: Control of Enzyme Activity • Many substances in the cell are produced by a

metabolic pathway (a series of many chemical reactions involving enzymes)

• Feedback inhibition = High levels of a substance will result in a decrease in its production