enzymes chapter 5. questions to answer! 1.what are enzymes? a.state the definition of enzymes. 2.how...

EnzymesEnzymesChapter 5

Questions to answer!1. What are enzymes?

a. State the definition of enzymes.2. How do enzymes work?

a. Explain the mode of action of enzymes in terms of active site, enzyme-substrate complex, lowering of activation energy, and enzyme specificity.

b. Describe the characteristics of enzymes.

3. What affects enzyme activity?a. Investigate and explain the effects of temperature,

pH, on the rate of enzyme-catalyzed reactions.3. Where are enzymes used?

a. State 1 enzyme-catalyzed process.b. Classify enzymes.

Lesson Lesson ObjectivesObjectives

Definition of Definition of EnzymesEnzymes

Enzymes are biological catalysts, commonly made of protein. They alter the rate of

chemical reactions without themselves being chemically changed at the end of the reaction.

What are What are enzymes?enzymes?

Recall: What are proteins??

What are catalysts? How do they work?

Properties of enzymes

Recall: ProteinsRecall: ProteinsWhat are What are enzymes?enzymes?

• Basic unit of proteins: • How amino acids are linked up: • Link between amino acids: • Long chains of basic units: • Polypeptides are folded and its 3D shape is held together

by .• Weak bonds can be broken by heat and chemicals. The

protein is said to be .• A denatured protein loses its .

amino acids

condensation reaction

peptide bond

polypeptide

weak bonds

denatured

function

Source: http://www.monroecc. edu/deps/pstc/backup/heme.gif

How do How do enzymes enzymes

work?work?

• A catalyst is a substance which can alter or speed up a chemical reaction.

• Catalysts are not chemically-changed at the end of the reaction.

Enzymes are Enzymes are Biological CatalystsBiological Catalysts


work?work?

Eg: Decomposition of Hydrogen Peroxide…

2H2O2 → 2H2O + O2

This reaction can be sped up by a catalyst, manganese (IV) oxide.

Videos:Dilute H2O2: H2O2 decompositionFresh H2O2: Last High School Chemistry Class

Source: http://pics.drugstore.com/prodimg/73864/200.jpg



work?work?

Eg: Decomposition of Hydrogen Peroxide…

2H2O2 → 2H2O + O2

This reaction can be sped up by a catalyst, manganese (IV) oxide.

2H2O2 2H2O + O2 + Heat

The same amount of manganese (IV) oxide remains after the reaction. It is not changed during the

reaction.

Inorganic Catalyst

MnO2 (catalyst)



work?work?

The enzyme CATALASE can speed up hydrogen peroxide decomposition.

Enzymes are BIOLOGICAL CATALYSTS.

Video: Nosebleed Chemistry

2H2O2 2H2O + O2 + Heat

Biological Catalyst(Organic)

Note: Catalase is

also found in potatoes!

Catalase (enzyme)


How do enzymes work?

How do enzymes work?

Activation Activation EnergyEnergy


work?work?

• The energy needed to start a chemical reaction is called activation energy.

• Once the reaction has received enough energy, the rest of the reaction occurs spontaneously.

Activation Activation EnergyEnergy


work?work?

• Enzymes lower the activation energy required to start a chemical reaction.

Reactants

Products

• Enzymes do not change the energy level of reactants and products.

• Enzymes only lower the ‘height’ of the ‘activation energy hill.’

Lock and Key Lock and Key HypothesisHypothesis


work?work?

• The substances on which enzymes act are called substrates.• Enzymes bind to substrates by the lock and key hypothesis.

active sites

A

B

enzyme molecule (the ‘lock’)

substrate molecules (A and B) can fit into the active sites

enzyme-substrate complex

AB

enzyme molecule is free to take part in another reaction

a new substance (product) AB leaves the active sites

Lock and Key Lock and Key HypothesisHypothesis


work?work?

• Enzyme reaction depends on the presence of active sites.• Active sites have a specific 3D shape.• Specific substrate molecules fit into the active site like a

lock and key.• Substrate binds to the enzyme, forming an enzyme

substrate complex.• Reactions take place at the active sites to convert

substrate molecule(s) into product molecule(s).• Product molecule(s) separate, leaving the enzyme

molecule unchanged and free to combine again with more substrate molecules.

Induced Fit Induced Fit ModelModel


work?work?

• Current hypothesis for enzyme action• When a substrate molecule fits into an enzyme molecule,

the enzyme molecule alters its shape slightly so that it fits more tightly around the substrate molecule.

• This makes the chemical reaction easier.

Lock and key hypothesis Induced Fit ModelSource: http://neurobio.drexel.edu/GalloWeb/loudon_enzymes.htm

Enzyme Enzyme CharacteristicsCharacteristics


work?work?

Enzymes are required in minute amounts• Enzymes are very efficient molecules.• They remain unchanged at the end of the reaction, and

thus can be reused over and over again.• A of enzyme can catalyze a

of chemical reactions.small amount large amount



work?work?

Enzyme Specificity• Enzyme action is highly specific: each chemical reaction is

catalyzed by a unique enzyme.• The enzyme’s specificity is due to its 3-dimensional

surface configuration.• The shape of the substrate must be complementary to

the shape of the enzyme’s active site.• The shape of an enzyme can be affected by high

temperature and acids and alkalis.



work?work?

Enzymes catalyze reversible reactions• Some reactions in living cells are reversible. They can

proceed in the forward or backward direction.• Some enzymes catalyze both forward and backward

reactions until an equilibrium is reached. This occurs when the amount of reactants equals the amount of products formed.



work?work?

Some enzymes require coenzymes• Some enzymes require a coenzyme (another compound)

to be bound to them before they can catalyze reactions.• Coenzymes are non-protein organic compounds.• Eg. of coenzymes: Vitamin B complex

4 Factors4 FactorsWhat affects What affects

enzyme enzyme activity?activity?

Enzymes are affected by the following:• Temperature• pH• Enzyme concentration• Substrate concentration

TemperatureTemperatureWhat affects What affects


• Enzymes have an optimum temperature.• This is the temperature at which the enzyme catalyzes the

largest number of reactions per second.• The optimum temperature of enzymes varies in different

organisms, and is often but not always close to the temperature at which the enzyme usually functions.

• Some enzymes may have very high or very low optimum temperatures.



Temperature

Rate of reaction (enzyme activity)

0 K (optimum temperature)

D

An enzyme is less active at very low temperatures.

1

As the temperature rises, enzyme activity increases as indicated by the increase in the rate of reaction it catalyses. Usually the enzyme is twice as active for every 10°C rise in temperature until the optimum temperature is reached.

2

The optimum temperature is reached. Enzyme is most active.

3

Beyond the optimum temperature, enzyme activity decreases.

4

At point D, the enzyme has lost its ability to catalyse the reaction.

5



As temperature rises…• Particles of matter are in constant random motion.• In the reaction, the enzyme and substrate molecules

move and collide with one another at random.• Raising the temperature increases the kinetic energy of

the molecules.• The substrate and enzyme molecules collide with each

other more often, increasing the chance of substrates fitting into active sites.

• The rate of formation of enzyme-substrate complex increases, increasing the rate of formation of products.



As temperature rises…• Enzyme activity increases as the temperature increases

up to the optimum temperature.• At high temperatures, enzyme activity decreases.• Enzymes are made of , and its 3D shape are

held together by .• At high temperatures, the vibrations of the atoms in the

enzyme vibrate so violently that they break the weak bonds in the enzyme.

• The enzyme loses its shape and becomes denatured.• The higher the temperature, the faster the rate of

denaturation.

weak bondsproteins

pHpHWhat affects What affects


• Enzymes are affected by the acidity or alkalinity of the solutions they are in.

• Acid or alkali can interact with the enzyme molecule, causing the protein to change its shape.

• Extreme changes in pH of the solutions denature the enzymes.

• Enzymes also have an optimum pH – the pH at which the enzyme can best function in.

pHpHWhat affects What affects


Enzyme & Substrate Enzyme & Substrate ConcentrationConcentration

What affects What affects enzyme enzyme activity?activity?

Enzyme & Substrate Enzyme & Substrate ConcentrationConcentration

What affects What affects enzyme enzyme activity?activity?

• In a solution of fixed enzyme concentration, as substrate concentration increases, the rate of reaction increases to a maximum.

• Beyond the maximum point, increasing the substrate concentration will not increase the rate of reaction.

• This is because at any point of time, all the enzyme molecules are in use. The enzyme molecules are saturated.

• The enzyme concentration becomes the limiting factor.• The reaction rate will increase if the enzyme

concentration is increased.

DigestionDigestionWhere are Where are enzymes enzymes

used?used?

• Some food molecules are large and insoluble in water.• These food molecules cannot through the cell

surface membrane.• Some examples of large food molecules are ,

and .• The large molecules must first be converted into simpler

smaller substances which are soluble in water and diffusible.

• This is known as digestion, and is achieved by digestive enzymes.

diffuse

proteinsstarch fats

DigestionDigestionWhere are Where are enzymes enzymes

used?used?

Enzymes are involved in two types of reactions in the body:1. Synthesis of complex substances from simpler ones2. Break down of complex substances to simpler ones

CONDENSATION REACTION

HYDROLYTIC REACTIONS

Examples of condensation reactions in the body:

• Forming from glucose

• Forming proteins from

Examples of hydrolysis in the body:• Large molecules of food are converted to

smaller molecules by digestive enzymes.• In cell respiration, glucose is broken down to

carbon dioxide and water and release energy.• Hydrogen peroxide can be produced in chemical

reactions in cells. It is toxic to tissues. Cells produce enzyme catalase which catalyses the breakdown of hydrogen peroxide.

Enzymes catalyze practically Enzymes catalyze practically ALLALL the chemical reactions that occur in the chemical reactions that occur in

an organism!an organism!

starch

amino acids

Classification of Classification of EnzymesEnzymes

• Enzymes are classified according to the chemical reactions they catalyze.

• Enzymes that catalyze hydrolytic reactions are known as hydrolases.

• Oxidation-reduction enzymes are involved in breaking down glucose during respiration.

• Enzymes were previously named by the persons who discovered them.

• Nowadays, enzymes are named according to a scientific system.

Where are Where are enzymes enzymes

used?used?

Classification of Classification of EnzymesEnzymes

Where are Where are enzymes enzymes

used?used?

Type of hydrolase Example(s)Carbohydrases digest carbohydrates

•Salivary amylase (in the mouth) and pancreatic amylase. Both digest starch.

•Cellulases digest cellulose. It is produced by some bacteria. It is not found in mammals.

Proteases digest proteins

•Pepsin in the stomach

Lipasesdigest lipids (fats)

•Lipase in pancreatic juice

Industrial UsesIndustrial UsesWhere are Where are enzymes enzymes

used?used?

• Enzymes are used in industry as they can bring about chemical changes at low temperature.

• Chemical reactions at low temperatures are easier to control and cheaper to run.

• Enzymes can be extracted from living cells and used in their pure form.

Industrial UsesIndustrial UsesWhere are Where are enzymes enzymes

used?used?

• Microorganisms producing useful enzymes can be used in industry to make cheese, yoghurt and beer.

• Catalase can be added to latex containing hydrogen peroxide to produce oxygen to form foam rubber.

• Enzyme specificity makes them ideal for use in analysing chemicals.– Enzymes can be used to detect glucose in urine.– This can help to detect diabetes.

Source: http://news.thomasnet.com/ images/large/011/11187.jpg

Source: http://www.southernbiological.com/Products/ Kits&Equipment/SpecialLabFieldEquipt/G10_36.htm

Enzymes

Biological catalysts

Proteins

TemperaturepHSubstrate concentration

Enzyme concentration

Inactivated Denatured

Coenzymes

Enzyme-substratecomplex

Lock-and-keyhypothesis

Induced-fitmodel

Specificproduct(s)

Rate of reaction

Chemical reactionsActivation

energy

Extracellular enzymes

Intracellular enzymes

Digestivesystem

Lipases Proteases Carbohydrases

Lipids Proteins Carbohydrates

Functions

have specific are

as

form speed up

affected by

are

at low at high

at extreme

with the help of

by

Specific bindingof enzyme

is the

to form

of

by lowering are

involve

examples

digest digest digest

Substrate

to

Fatty acids and glycerol

Amino acids

Simple sugars

to form to form to form

found in

Remain chemically unchanged at the end of the reaction

Pure Biology Chapter 5Definition of enzymes

Enzymes are biological catalysts, commonly made of protein. They

alter the rate of chemical reactions without themselves

being chemically changed at the end of the reaction.

Enzymes

Biological catalysts

Substrate concentration

Enzyme concentration

Inactivated Denatured

Coenzymes

Enzyme-substratecomplex

Induced-fitmodel

Specificproduct(s)

Rate of reaction

Chemical reactions

Extracellular enzymes

Intracellular enzymes

Lipases

Proteins Carbohydrates

Functions

have specific are

as

form speed up

affected by

are

at low at high

at extreme changes of

with the help of

by

Specific bindingof enzyme

is the

to form

of

by lowering are

involve

examples

digest digest digest

Substrate

to

Simple sugars

to form to form to form

found in

Remain chemically unchanged at the end of the reaction

Pure Biology Chapter 5Definition of enzymes

enzymes chapter 5. questions to answer! 1.what are enzymes? a.state the definition of enzymes. 2.how...

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