CH 5 continuedCH 5 continuedEnergy Energy

What Is Energy?What Is Energy? Capacity to do workCapacity to do work

Life depends on the fact that energy can be Life depends on the fact that energy can be converted from one form to anotherconverted from one form to another

Forms of energyForms of energy Potential energyPotential energy – stored energy – stored energy (chemical & positional)(chemical & positional)

Kinetic energyKinetic energy – energy of motion – energy of motion (heat, light, electricity)(heat, light, electricity)

Energy in Living OrganismsEnergy in Living Organisms

Examples of potential energy Examples of potential energy • Concentration gradientConcentration gradient• Energy stored in a chemical bondEnergy stored in a chemical bond

• the potential energy of moleculesthe potential energy of molecules

Examples of kinetic energy Examples of kinetic energy • Light, heat, electricityLight, heat, electricity

• Transport of substancesTransport of substances

• Muscle contractionsMuscle contractions

Thermodynamics: study of energy transformationsThermodynamics: study of energy transformations

The First Law of ThermodynamicsThe First Law of Thermodynamics• Energy in the universe is constantEnergy in the universe is constant

Energy can be changed from one form to another but cannot Energy can be changed from one form to another but cannot be created or destroyedbe created or destroyed

• When one form of energy is converted to another the When one form of energy is converted to another the total energy present remains the sametotal energy present remains the same

Examples – firefly converts chemical/potential energy in food to Examples – firefly converts chemical/potential energy in food to kinetic energy (light and heat)kinetic energy (light and heat)

Thermodynamics: study of energy transformationsThermodynamics: study of energy transformations

The Second Law of ThermodynamicsThe Second Law of Thermodynamics• Energy transformations increase the disorder of the Energy transformations increase the disorder of the

universe (entropy)universe (entropy)

• Each energy transformation releases some of the Each energy transformation releases some of the energyenergy as as heat heat

The increased movement of the particles due to the heat The increased movement of the particles due to the heat increases their disorderincreases their disorder

Say the energy become “less concentrated” – more spread outSay the energy become “less concentrated” – more spread out

Fuel

Gasoline

Energy conversion in a cell

Energy for cellular work

Cellular respiration

Waste productsEnergy conversion

Combustion

Energy conversion in a carOxygen

Heat

Glucose

Oxygen Water

Carbon dioxide

Water

Kinetic energyof movement

Heatenergy

Carbon dioxide

Energy and CellsEnergy and Cells

Each time a cell releases energy stored in Each time a cell releases energy stored in chemical bonds that energy is:chemical bonds that energy is: Captured in new, lower energy bonds, and/or Captured in new, lower energy bonds, and/or

used to do the work of the cell used to do the work of the cell andand

some is released as heat. some is released as heat. • Cells cannot use heat to do the work of the cellCells cannot use heat to do the work of the cell

Chemical reactionsChemical reactions either either storestore or or release energyrelease energy

Endergonic reactions Endergonic reactions • Require an input of energy from the surroundingsRequire an input of energy from the surroundings• Yield products higher in potential energy than Yield products higher in potential energy than

reactantsreactants• Example: photosynthesisExample: photosynthesis

Exergonic reactions Exergonic reactions • Release energy Release energy • Yield products that contain less potential energy than Yield products that contain less potential energy than

their reactantstheir reactants• Examples: cellular respiration, burningExamples: cellular respiration, burning

Reactants

Products

Amount ofenergy

required

Po

ten

tial

en

erg

y o

f m

ole

cule

s

Energy required

Endergonic reactionEndergonic reaction

Examples of Endergonic ReactionsExamples of Endergonic Reactions

Reactions that Reactions that require an input require an input of energyof energy PhotosynthesisPhotosynthesis

• Multi-step process in which the sun’s energy is Multi-step process in which the sun’s energy is used to convert COused to convert CO22 and water into high energy and water into high energy

sugar molecules sugar molecules

Synthesis of ATPSynthesis of ATP• ADP + P + energy ADP + P + energy ATP ATP

Energy released

Po

ten

tial

en

erg

y o

f m

ole

cule

s

Reactants

Products

Amount ofenergy

released

Exergonic reactionExergonic reaction

Examples of Exergonic ReactionsExamples of Exergonic Reactions

Reactions that Reactions that releaserelease energy energy Cellular respirationCellular respiration

• Multi-step process by which energy stored in Multi-step process by which energy stored in glucose is releasedglucose is released

• Some of the energy released is used to make ATPSome of the energy released is used to make ATP• Some of the energy is released as heatSome of the energy is released as heat

Hydrolysis of ATPHydrolysis of ATP• ATP ATP ADP + P + energy ADP + P + energy

Chemical reactions either release or store Chemical reactions either release or store energyenergy

A living organism produces thousands of A living organism produces thousands of endergonic and exergonic chemical reactionsendergonic and exergonic chemical reactions– All of these combined is called All of these combined is called metabolismmetabolism– A A metabolic pathwaymetabolic pathway is a series of chemical is a series of chemical

reactions that either break down a complex reactions that either break down a complex molecule or build up a complex moleculemolecule or build up a complex molecule

Copyright © 2009 Pearson Education, Inc.

Energy CouplingEnergy Coupling

Coupled ReactionsCoupled Reactions Energy given off by the exergonic Energy given off by the exergonic

reaction is used to fuel/drive the reaction is used to fuel/drive the endergonic reactionendergonic reaction

Examples:Examples:• Active transportActive transport• First step of glycolysisFirst step of glycolysis

ATPATP

ATP is the cell’s primary energy carrierATP is the cell’s primary energy carrier

ATP = adenosine triphosphateATP = adenosine triphosphate ATP = 1 adenine, 1 ribose, and 3 phosphates ATP = 1 adenine, 1 ribose, and 3 phosphates

(nucleotide)(nucleotide) The energy in an ATP molecule is in the The energy in an ATP molecule is in the

bonds between phosphatesbonds between phosphates

The hydrolysis of ATP releases energy.The hydrolysis of ATP releases energy.

Adenosine Triphosphate

Phosphategroup

P P P

H2O

Hydrolysis

ATP ADPRibose

Adenine

Adenosine diphosphate

P P P Energy

ATP shuttles chemical energy and drives ATP shuttles chemical energy and drives cellular workcellular work

Hydrolysis of ATP releases energy by Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to transferring its third phosphate from ATP to some other moleculesome other molecule– The transfer is called phosphorylationThe transfer is called phosphorylation– In the process, ATP energizes moleculesIn the process, ATP energizes molecules

Copyright © 2009 Pearson Education, Inc.

How Enzymes FunctionHow Enzymes Function

Even with an abundant source of ATP Even with an abundant source of ATP chemical reactions in cells would not occur chemical reactions in cells would not occur without the presence of catalysts called without the presence of catalysts called enzymes. enzymes.

How Enzymes FunctionHow Enzymes Function

Chemical reactions require an input of Chemical reactions require an input of energy to get startedenergy to get started Called the activation energy (ECalled the activation energy (EAA))

Reactions with a large EReactions with a large EA A are relatively slow.are relatively slow.• Enzymes lower the activation energy Enzymes lower the activation energy

All reactions in the cell require the presence of All reactions in the cell require the presence of a specific enzymea specific enzyme

Reactants

Netchangein energy

EA withoutenzyme

Products

Progress of the reaction

En

erg

y

EA withenzyme

Enzymes = proteins that function as biological catalystsEnzymes = proteins that function as biological catalysts• Increase the rate of a reaction without themselves being changedIncrease the rate of a reaction without themselves being changed• Decrease the energy of activation needed to begin a reactionDecrease the energy of activation needed to begin a reaction

Enzymes and SubstratesEnzymes and Substrates

Enzymes are substrate specificEnzymes are substrate specific Each enzyme has a unique three-dimensional Each enzyme has a unique three-dimensional

shape that determines which chemical shape that determines which chemical reaction it catalyzesreaction it catalyzes

What determines the enzyme’s 3-D shape?What determines the enzyme’s 3-D shape?

Enzymes and SubstratesEnzymes and Substrates

Terms:Terms: Substrate:Substrate: the reactant that fits into the active the reactant that fits into the active

site of an enzymesite of an enzyme

Active site:Active site: a pocket on the enzyme’s surface a pocket on the enzyme’s surface that the substrate attaches tothat the substrate attaches to

Each active site binds only specific substratesEach active site binds only specific substrates

Induced Fit ModelInduced Fit Model

Binding of the substrate causes the enzyme to Binding of the substrate causes the enzyme to change shape and hold the substrates more change shape and hold the substrates more tightly.tightly. This creates conditions that are ideal for the reaction This creates conditions that are ideal for the reaction

by:by:• Holding reactants close togetherHolding reactants close together• Orienting reactants properlyOrienting reactants properly• Straining bondsStraining bonds• Shutting out / bringing in waterShutting out / bringing in water• Creating an acid or base environmentCreating an acid or base environment

Enzyme availablewith empty activesite

Active site

Glucose

Fructose

Products arereleased

Enzyme(sucrase)

Substrate(sucrose)

H2O

Substrate isconverted toproducts

Substrate bindsto enzyme withinduced fit

Enzyme SummaryEnzyme Summary

Most enzymes are proteins. Most enzymes are proteins. Speed up reactions by lowering the ESpeed up reactions by lowering the EA A

Enzymes are substrate specific Enzymes are substrate specific Enzymes are not permanently changed in the Enzymes are not permanently changed in the

reaction.reaction.• Enzymes can be used over and over again.Enzymes can be used over and over again.

A single enzyme may act on thousands or A single enzyme may act on thousands or millions of substrate molecules per second!millions of substrate molecules per second!

Cellular Environment and EnzymesCellular Environment and Enzymes

Enzymes must be in their correct 3-D Enzymes must be in their correct 3-D shape to functionshape to function Each enzyme functions at its best under a Each enzyme functions at its best under a

specific set of conditions. specific set of conditions. • TemperatureTemperature• pHpH• SalinitySalinity

Why do these conditions matter?Why do these conditions matter?

Temperature and Enzyme ActivityTemperature and Enzyme Activity

Activity Data for 3 EnzymesActivity Data for 3 Enzymes

Co-factorsCo-factors

Some enzymes require Some enzymes require cofactorscofactors to to functionfunction

• Metal ionsMetal ions Such as ions of iron, zinc, and calciumSuch as ions of iron, zinc, and calcium

• Organic molecules called coenzymesOrganic molecules called coenzymes The B vitamins are all coenzymesThe B vitamins are all coenzymes

Enzyme InhibitorsEnzyme Inhibitors

Inhibitors are substances that interfere Inhibitors are substances that interfere with an enzyme’s ability to function with an enzyme’s ability to function Many toxins/poisons are enzyme inhibitorsMany toxins/poisons are enzyme inhibitors

• For example: Mercury binds to sulfur groups on For example: Mercury binds to sulfur groups on enzymes and cause the enzyme to change shape enzymes and cause the enzyme to change shape and lose functionand lose function

Enzyme InhibitorsEnzyme Inhibitors

Inhibitors may bind to the enzyme with Inhibitors may bind to the enzyme with covalent bonds or H bondscovalent bonds or H bonds Covalent bonding inhibitors Covalent bonding inhibitors IrreversibleIrreversible

inhibitioninhibition

H bonding inhibitors H bonding inhibitors ReversibleReversible inhibition inhibition

More on Enzyme InhibitorsMore on Enzyme Inhibitors

Irreversible enzyme inhibitorsIrreversible enzyme inhibitors have many have many uses.uses. Some inhibitors are deadlySome inhibitors are deadly

• Cyanide – inhibits an enzyme needed to make Cyanide – inhibits an enzyme needed to make ATPATP

• Sarin – inhibits an enzyme needed for nerve Sarin – inhibits an enzyme needed for nerve transmissiontransmission

• Pesticides and herbicides – bind to key enzymes in Pesticides and herbicides – bind to key enzymes in insects and plantsinsects and plants

More on Enzyme InhibitorsMore on Enzyme Inhibitors

Some inhibitors are beneficialSome inhibitors are beneficial Antibiotics bind to essential enzymes found in Antibiotics bind to essential enzymes found in

bacteriabacteria• Enzymes not found in eukaryotic cellsEnzymes not found in eukaryotic cells

Protease inhibitors are HIV drugs that bind to Protease inhibitors are HIV drugs that bind to and inhibit an essential viral enzymeand inhibit an essential viral enzyme

Types of InhibitorsTypes of Inhibitors

Competitive inhibitorsCompetitive inhibitors – compete with the – compete with the substrate for binding at the active sitesubstrate for binding at the active site Competitive inhibitors are similar in structure Competitive inhibitors are similar in structure

to the “real” substrateto the “real” substrate

Types of InhibitorsTypes of Inhibitors

Noncompetitive inhibitorsNoncompetitive inhibitors – bind to the – bind to the enzyme at a location other than the active enzyme at a location other than the active sitesite Binding changes the shape of the active site Binding changes the shape of the active site

so that the substrate cannot bindso that the substrate cannot bind• Called Called allosteric controlallosteric control

Release of the inhibitor returns the active site Release of the inhibitor returns the active site to its proper shapeto its proper shape

Substrate

Enzyme

Active site

Normal binding of substrate

Competitiveinhibitor

NoncompetitiveInhibitor -- also called an allostericinhibitor

Enzyme inhibition

• A A competitive inhibitorcompetitive inhibitor takes the place of a takes the place of a substrate in the active sitesubstrate in the active site

• A A noncompetitive inhibitornoncompetitive inhibitor alters an alters an enzyme's function by binding at a location enzyme's function by binding at a location other than the active site and the binding other than the active site and the binding changes the shape of the active sitechanges the shape of the active site Also called - allosteric controlAlso called - allosteric control

Feedback Inhibition of Tryptophan Feedback Inhibition of Tryptophan SynthesisSynthesis

enzyme 2 enzyme 3 enzyme 4 enzyme 5

enzyme 1

SUBSTRATE

END PRODUCT

(tryptophan)

enzyme activity of the first enzyme is enzyme activity of the first enzyme is blocked by the end-product of the pathwayblocked by the end-product of the pathway

Tryptophan builds up in the cell, binds to the first enzyme in the pathway, the active site changes shape so that it cannot bind the first substrate, and tryptophan synthesis stops

Feedback InhibitionFeedback Inhibition

When the cell needs to make tryptophan When the cell needs to make tryptophan again:again: the tryptophan will detach from the enzymethe tryptophan will detach from the enzyme the enzyme will resume its original shape and the enzyme will resume its original shape and

bind substrate #1 againbind substrate #1 again

Many metabolic pathways in the cell are Many metabolic pathways in the cell are controlled by feedback inhibition.controlled by feedback inhibition.