Cells & EnzymesCells & Enzymes

Section 2Section 2

CatalystsCatalysts

The rate chemical reaction can be speeded up The rate chemical reaction can be speeded up by raising the by raising the temperaturetemperature or adding a or adding a catalystcatalyst

A catalyst is not changed by the reaction so it A catalyst is not changed by the reaction so it can be can be re-usedre-used

An artificial catalyst used to speed up the An artificial catalyst used to speed up the breakdown of hydrogen peroxide is breakdown of hydrogen peroxide is manganese manganese dioxidedioxide

EnzymesEnzymes

EnzymesEnzymes are biological catalysts and are are biological catalysts and are found in found in allall living cells living cells

The enzyme that speeds up the The enzyme that speeds up the breakdown of breakdown of hydrogen peroxide hydrogen peroxide into into water and oxygen is called water and oxygen is called catalasecatalase

HYDROGEN PEROXIDE OXYGEN + WATERcatalase

The Nature of EnzymesThe Nature of Enzymes

There are thousands of different enzymes working in There are thousands of different enzymes working in your bodyyour body

Why are there so many different enzymes?Why are there so many different enzymes?

Each enzyme has its own substrate and no other Each enzyme has its own substrate and no other enzyme can work on that substrateenzyme can work on that substrate

The substrate of an enzyme is the substance it The substrate of an enzyme is the substance it works on e.g. hydrogen peroxide is the works on e.g. hydrogen peroxide is the substrate for the enzyme catalase.substrate for the enzyme catalase.

Lock & Key TheoryLock & Key Theory

Enzymes are made fromEnzymes are made from

An enzyme can only work on it’s own An enzyme can only work on it’s own specific substratespecific substrate

For this reason an enzyme’s action is said For this reason an enzyme’s action is said to be to be SPECIFICSPECIFIC

Similar to a lock and key – onlySimilar to a lock and key – only

one specific one specific keykey (substrate) will (substrate) will

fit into a specific fit into a specific locklock (enzyme) (enzyme)

proteinsproteins

Each enzyme has a particular area on its Each enzyme has a particular area on its surface called an surface called an active siteactive site

The active site matches the shape of the The active site matches the shape of the enzyme’s substrate so it can join to the enzyme’s substrate so it can join to the enzyme enzyme complimentarycomplimentary

This substrate will not works with the enzyme because the shape is not complimentary to

the enzyme

Types of ReactionsTypes of Reactions

Enzymes can be involved in two different Enzymes can be involved in two different types of reactions:types of reactions:

• Breakdown (Degradation) ReactionsBreakdown (Degradation) Reactions

• Building-Up (Synthesis) ReactionsBuilding-Up (Synthesis) Reactions

Breakdown ReactionsBreakdown Reactions

Breakdown or Breakdown or degradationdegradation reactions reactions convert large molecules into smaller onesconvert large molecules into smaller ones

An example of this is the breakdown of An example of this is the breakdown of largelarge starch molecules into starch molecules into smallersmaller maltose molecules by amylasemaltose molecules by amylase

AmylaseAmylase is found naturally in is found naturally in salivasaliva

Breakdown ReactionsBreakdown Reactions

StarchStarch is broken down by the enzyme .…….… is broken down by the enzyme .…….… to ……….. sugar moleculesto ……….. sugar molecules

STARCH STARCH AMYLASEAMYLASE

MALTOSEMALTOSE

Large starch molecule Small maltose molecules

amylaseamylasemaltosemaltose

Breakdown ReactionsBreakdown ReactionsHydrogen PeroxideHydrogen Peroxide is broken down into ……… and ……….. gas by the enzyme ………… is broken down into ……… and ……….. gas by the enzyme …………

HYDROGEN PEROXIDE HYDROGEN PEROXIDE CATALASECATALASE

WATER+OXYGEN WATER+OXYGEN

waterwateroxygenoxygen catalasecatalase

Breakdown ReactionsBreakdown ReactionsSucroseSucrose is broken down into ……….. and ………… by the enzyme ………… is broken down into ……….. and ………… by the enzyme …………

SUCROSESUCROSEINVERTASEINVERTASE

GLUCOSE + FRUCTOSEGLUCOSE + FRUCTOSE

glucoseglucoseinvertaseinvertasefructosefructose

S FG

Breaking Down Protein

Protein is another large, insoluble, molecule that needs to be broken down into smaller, soluble, units so that it can get across the cell membrane and into our bodies

Protein is broken down into polypeptides by the enzyme pepsin

Protein pepsin Polypeptides

Breaking Down Fats

Fats must be broken down into smaller units called fatty acids and glycerol

Fats must be broken down so we can absorb them into our bodies

The enzyme lipase helps to break down the fats

Fats lipase Fatty acids + Glycerol

Synthesis ReactionsSynthesis Reactions

Build-up or synthesis Build-up or synthesis reactions convert small reactions convert small molecules to larger onesmolecules to larger ones

An example of this is the An example of this is the build up of starch from build up of starch from glucose-1-phosphate glucose-1-phosphate moleculesmolecules

The build up of glucose-1-phosphate in plants

Leaves make glucose

• Some used as energy for growth

• Some transported to root for storage

• Once in roots glucose is converted to glucose-1-phosphate

• The enzyme phosphorylase converts lots of glucose-1-phosphate into a larger starch molecule

Glucose-1-phosphate phosphorylase Starch

Phosphorylase ExperimentPhosphorylase Experiment

AimAim: to show that starch is being : to show that starch is being synthesised when the substrate and synthesised when the substrate and enzyme are both presentenzyme are both present

Row A: glucose-1-phosphate and phosphorylase

Row B: glucose-1-phosphate and distilled water

Row C: distilled water

and phosphorylase

Row A: glucose-1-phosphate and phosphorylase

Row B: glucose-1-phosphate and distilled water

Row C: distilled water

and phosphorylase

Row A was the only one that gave a positive result with iodine solution. This means that there was starch present in row A only.

This experiment proves that in order to synthesise starch from glucose-1-phosphate and the enzyme phosphorylase must be present.

ControlsControls

Row A: glucose-1-phosphate and phosphorylase

Row B: glucose-1-phosphate and distilled water

Row C: distilled water

and phosphorylase

Rows B and C where used as controls in this experiment to prove that both the enzyme and the substrate were needed together to synthesise starch.

Digestive EnzymesDigestive Enzymes

Each enzyme has an Each enzyme has an optimum pHoptimum pH

Mouth = pH 7 amylaseMouth = pH 7 amylase

Stomach = pH 2 pepsinStomach = pH 2 pepsin

Small Intestine = pH 9 trypsinSmall Intestine = pH 9 trypsin

Most enzymes that work in the body have an optimum temperature of 37°C

The pH ScaleThe pH Scale

1 2 3 4 5 6 7 8 9 10 11 12 13 141 2 3 4 5 6 7 8 9 10 11 12 13 14

Acid Alkali

Neutral

…. ….

Strong Acid

Strong Alkali

Weak Alkali

Weak Acid

Effects of TemperatureEffects of Temperature

Like you, enzymes like to be at a comfortable Like you, enzymes like to be at a comfortable temperature to work at their maximum ratetemperature to work at their maximum rate

If the temperature is too low, there is not enough If the temperature is too low, there is not enough energy for the reaction to goenergy for the reaction to go

By increasing the temperature, the rate of reaction will By increasing the temperature, the rate of reaction will increase because there is more energy for the reactionincrease because there is more energy for the reaction

After a certain temperature, the reaction will start to After a certain temperature, the reaction will start to decrease rapidlydecrease rapidly to zero to zero

Effects of TemperatureEffects of Temperature

When enzymes reach a particular temperature, When enzymes reach a particular temperature, they will work at their maximum capacity.they will work at their maximum capacity.

The temperature at which an enzyme works best The temperature at which an enzyme works best is known as the is known as the optimumoptimum temperature. temperature.

If the temperature continues to rise, the If the temperature continues to rise, the enzyme’s shape will eventually be destroyed. enzyme’s shape will eventually be destroyed. We say that the enzyme has beenWe say that the enzyme has been denatured. denatured.

Effects of TemperatureEffects of Temperature

DenaturingDenaturing

If an enzyme is If an enzyme is denatureddenatured it’s shape will it’s shape will changechange

Enzyme will no longer Enzyme will no longer be be complimentarycomplimentary to the to the shape of the substrateshape of the substrate

Excessive heatExcessive heat can can cause an enzyme to be cause an enzyme to be denatureddenatured

37°C

60°C