Chapter 6Chapter 6

Energy FlowEnergy Flowin Cellsin Cells

Chapter 6 2 The Laws of ThermodynamicsThe Laws of Thermodynamics

First Law of ThermodynamicsFirst Law of Thermodynamics• Energy can neither be created nor destroyedEnergy can neither be created nor destroyed• The total amount of energy within a given The total amount of energy within a given

system remains constant unless energy is system remains constant unless energy is added or removed from the systemadded or removed from the system

The Second Law of ThermodynamicsThe Second Law of Thermodynamics• The amount of useful energy decreases when The amount of useful energy decreases when

energy is converted from one form to anotherenergy is converted from one form to another• EntropyEntropy (disorder) increases (disorder) increases

Chapter 6 3

Chapter 6 4 Energy of SunlightEnergy of Sunlight

Living things must gain external energy Living things must gain external energy in order to counteract the increase in in order to counteract the increase in their entropytheir entropy

• Photosynthetic organisms use external Photosynthetic organisms use external solar energy to maintain orderly solar energy to maintain orderly structurestructure

• Non-photosynthetic organisms use Non-photosynthetic organisms use stored chemical energy in other living stored chemical energy in other living things to counter increasing entropythings to counter increasing entropy

Chapter 6 5

Exergonic ReactionsExergonic Reactions

EnergyEnergycontentcontent

ofofmoleculesmolecules

highhigh

lowlow

(a)(a) Burning glucose (sugar):Burning glucose (sugar):an exergonic reactionan exergonic reaction

Progress of reactionProgress of reaction

Activation energy neededActivation energy neededto ignite glucoseto ignite glucose

Activation energy neededActivation energy neededto ignite glucoseto ignite glucose

Glucose + OGlucose + O22Glucose + OGlucose + O22

Energy released byEnergy released byburning glucoseburning glucose

Energy released byEnergy released byburning glucoseburning glucose

C OC O22 + H + H22OOC OC O22 + H + H22OO

Chapter 6 6

Exergonic ReactionsExergonic Reactions

EnergyReleased

++

++High EnergyHigh EnergyReactantsReactants

Low EnergyLow EnergyProductsProducts

OHO

OCH2OH

O O

O OC

OHH

Chapter 6 7

Endergonic ReactionsEndergonic Reactions

EnergyEnergycontentcontent

ofofmoleculesmolecules

highhigh

lowlow

(b)(b) Photosynthesis:Photosynthesis:an endergonic reactionan endergonic reaction

Progress of reactionProgress of reaction

GlucoseGlucoseGlucoseGlucose

Net energyNet energycaptured bycaptured bysynthesizingsynthesizing

glucoseglucose

COCO22 + H + H22OOCOCO22 + H + H22OO

ActivationActivationenergy fromenergy from

light capturedlight capturedby photosynthesisby photosynthesis

Chapter 6 8

Endergonic ReactionsEndergonic Reactions

++

Low EnergyLow EnergyReactantsReactants ++

High EnergyHigh EnergyProductsProducts

OHO

OCH2OH

O O

O OC

OHH

EnergySupplied

Chapter 6 9

Coupled ReactionsCoupled Reactions

Chapter 6 10

========

Phosphorylation & ATPPhosphorylation & ATP

Chapter 6 11

ATPATP versus versus ADP:ADP:Structural DifferencesStructural Differences

OH

PPO

O

O PP OH

OH

O

~~RiboseRibose

HH22CCHH22CC

HHHH

OOOO

HHHH

OHOHOHOHOHOHOHOH

HHHHHHHH

NNNNHCHCHCHC

NNNN CCCC

CCCC

CCCC

CHCHCHCH

NNNN

NNNN

NHNH22NHNH22

AdenineAdenine

Adenosine

Adenosine

PP OH

OH

O

OH

PPO

O

O PP O

OH

O

~~RiboseRibose

HH22CCHH22CC

HHHH

OOOO

HHHH

OHOHOHOHOHOHOHOH

HHHHHHHH

NNNNHCHCHCHC

NNNN CCCC

CCCC

CCCC

CHCHCHCH

NNNN

NNNN

NHNH22NHNH22

AdenineAdenine

Adenosine

Adenosine

~~

DiPhosphateDiPhosphate

TriPhosphateTriPhosphate

ADPADP

ATPATP

High-energyHigh-energyPhosphatePhosphate

BondBond

Chapter 6 12

Coupled ReactionsCoupled Reactionswithin Living Cellswithin Living Cells

Chapter 6 13

Electron CarriersElectron Carriers

Chapter 6 14

Metabolic PathwaysMetabolic Pathways

AA BB CC DDDD EEEE

FFFF GGGG

Enzyme 1Enzyme 1 Enzyme 2Enzyme 2 Enzyme 3Enzyme 3 Enzyme 4Enzyme 4

Enzyme 5Enzyme 5 Enzyme 6Enzyme 6

InitialInitialReactantsReactants

IntermediatesIntermediates FinalFinalProductsProducts

Pathway 1Pathway 1Pathway 1Pathway 1

Pathway 2Pathway 2Pathway 2Pathway 2

Chapter 6 15

EnergyEnergycontentcontent

ofofmoleculesmolecules

highhigh

lowlowProgress of reactionProgress of reaction

ActivationActivationenergy withoutenergy without

catalystcatalyst

ActivationActivationenergy withenergy with

catalystcatalyst

Activation Energy:Activation Energy:Controls Rate of ReactionControls Rate of Reaction

Chapter 6 16

Enzyme-Substrate InteractionsEnzyme-Substrate InteractionsSubstrateSubstrateSubstrateSubstrateSubstrateSubstrateSubstrateSubstrate

EnzymeEnzymeEnzymeEnzyme

ActiveActiveSiteSite

ActiveActiveSiteSite

11 Substrates Substrates enter active enter active sitesite

11 Substrates Substrates enter active enter active sitesite

22 Shape change Shape change promotes reactionpromotes reaction

22 Shape change Shape change promotes reactionpromotes reaction

33 Product released;Product released;enzyme ready againenzyme ready again

33 Product released;Product released;enzyme ready againenzyme ready again

Chapter 6 17

Enz. 5Enz. 5Enz. 5Enz. 5DDDD

Enz. 4Enz. 4Enz. 4Enz. 4CCCC

Enz. 3Enz. 3Enz. 3Enz. 3BBBB

Enzyme Regulation:Enzyme Regulation:Feedback InhibitionFeedback Inhibition

Enz. 2Enz. 2Enz. 2Enz. 2AAAA

Feedback InhibitionFeedback InhibitionIsoleucine inhibits enzyme 1Isoleucine inhibits enzyme 1

Enz. 1Enz. 1Enz. 1Enz. 1

CHCH33CHCH33

CCCC

CCCC

COOHCOOHCOOHCOOH

OHOHOHOH

NHNH33NHNH33HHHH

HHHHCHCH22

CHCH22

CCCC

CCCC

COOHCOOHCOOHCOOH

CHCH33CHCH33

NHNH33NHNH33HHHH

HHHH

CHCH33CHCH33

ThreonineThreonine(substrate)(substrate)ThreonineThreonine(substrate)(substrate) IsoleucineIsoleucine

(end product)(end product)IsoleucineIsoleucine

(end product)(end product)

Chapter 6 18

Enzyme Regulation: AllostericEnzyme Regulation: AllostericRegulation & Competitive InhibitionRegulation & Competitive Inhibition

SubstrateSubstrateSubstrateSubstrate

EnzymeEnzymeEnzymeEnzyme

Active Active SiteSite

Active Active SiteSite

Allosteric Allosteric Regulatory Regulatory SiteSite

Allosteric Allosteric Regulatory Regulatory SiteSite

(a)(a)

Allosteric Allosteric Regulatory Regulatory

MoleculeMolecule

Allosteric Allosteric Regulatory Regulatory

MoleculeMolecule

Shape of activeShape of activesite changedsite changed(b)(b)

(c)(c)

Competitive inhibitorCompetitive inhibitoroccupies active siteoccupies active site

Chapter 6 19 Environmental ConditionsEnvironmental Conditions

Three-dimensional structure of an enzyme Three-dimensional structure of an enzyme is sensitive to pH, salts, temperature, is sensitive to pH, salts, temperature, and presence of coenzymesand presence of coenzymes

Enzyme structure is distorted and function Enzyme structure is distorted and function is destroyed when pH is too high or lowis destroyed when pH is too high or low

Salts in an enzyme’s environment can also Salts in an enzyme’s environment can also destroy function by altering structuredestroy function by altering structure

Chapter 6 20 Environmental ConditionsEnvironmental Conditions

Temperature also affects enzyme activityTemperature also affects enzyme activity• Low temperatures slow down molecular Low temperatures slow down molecular

movementmovement• High temperatures cause enzyme shape High temperatures cause enzyme shape

to be altered, destroying functionto be altered, destroying function

Most enzymes function optimally only Most enzymes function optimally only within a very narrow range of these within a very narrow range of these conditionsconditions

Chapter 6 21

Chapter 6 22

Chapter 6Chapter 6

The endThe end