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HowCellsObtainEnergyBIOL 100

Ch. 3

Metabolism•  Metabolism

•  Thetotalityofanorganism’s

chemicalreac9ons

•  Sumofanabolismand

catabolism

•  emergentpropertyoflifethat

arisesfrominterac9onsbetween

moleculeswithinthecell

•  Butinacontrolledmanner…

•  homeostasis

MetabolicPathways

•  Metabolicpathway

•  beginswithaspecificmolecule

•  andendswithaspecific

product

•  Eachstepiscatalyzedbya

specificenzyme

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•  Catabolicpathways

•  Releaseenergybybreakingdowncomplexmoleculesintosimplercompounds

•  Cellularrespira4on

•  Thebreakdownofglucoseinthepresenceofoxygen

•  Anabolicpathways

•  Consumeenergytobuildcomplexmoleculesfromsimplerones

•  Ie-Thesynthesisofproteinfromaminoacids

•  Bioenerge4cs

•  Thestudyofhoworganismsmanagetheirenergyresources

•  Alllifeboilsdowntoenergybudget

Catabolism

•  Kine4cenergy

•  energyassociatedwithmo9on

•  Heat(thermalenergy)

•  kine9cenergyassociatedwithrandommovementofatomsormolecules

•  Poten4alenergy

•  energythatmaJerpossessesbecauseofitsloca9onorstructure

•  Chemicalenergy

•  poten9alenergyavailableforreleaseinachemicalreac9on

•  Energycanbeconvertedfromoneformtoanother

TypesofEnergy

TheLawsofEnergyTransforma9on•  Thermodynamics

•  Thestudyofenergytransforma9ons

•  Closedsystem

•  Isolatedfromitssurroundings

•  Liquidinathermos

•  Opensystem

•  EnergyandmaJercanbetransferredbetweenthesystemanditssurroundings

•  Organismsareopensystems

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TheFirstLawofThermodynamics•  Firstlawofthermodynamics(LawofConserva9onofEnergy)

•  Theenergyoftheuniverseisconstant:

–Energycannotbecreatedordestroyedbuttransferredand/ortransformed

TheSecondLawofThermodynamics•  Secondlawofthermodynamics:

–Everyenergytransferortransforma5onincreasestheentropy(disorder)oftheuniverse

•  Duringeveryenergytransferortransforma9on

•  Someenergyisunusable,oSenlostasheat

•  Increasesentropy

Fuel

Gasoline

Waste products Energy conversion

Combustion

Energy conversion in a car

Oxygen Water

Carbon dioxide

Kinetic energy of movement

Heat energy

•  Livingcellsunavoidablyconvert

organizedformsofenergyto

heat

•  2ndlaw

•  Spontaneousprocessesoccur

withoutenergyinput

•  canhappenquicklyorslowly

•  tooccurwithoutenergy

input

•  mustincreasethe

entropyoftheuniverse

•  Generallycorrespondsto

breakdown

Energy

Energy conversion in a cell Energy for cellular work

Cellular respiration

Heat

Glucose

Oxygen Water

Carbon dioxide

Fuel Energy conversion Waste products

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BiologicalOrderandDisorder•  Cells

•  Createorderedstructuresfromless

orderedmaterials

•  Anabolism

•  Equalslessentropy

•  Requirestheinputofenergy

•  Cells

•  AlsoreplaceorderedformsofmaJer

andenergywithlessorderedforms

•  Catabolism

•  Energyflowsintoanecosystemintheform

oflightandexitsintheformofheat

•  Evolu9onyieldsmorecomplexorganisms

•  Doesnotviolatethesecondlawofthermodynamics

•  Entropy(disorder)maydecreaseinanorganism

•  buttheuniverse’stotalentropyincreases

•  cellsdismantle(catabolic)macromoleculestomaketheirown

(anabolic)

OrderandDisorder

FreeEnergy,Stability,andEquilibrium•  Freeenergy

•  measureofasystem’sinstability,its

tendencytochangetoamorestablestate

•  Duringspontaneouschange

•  freeenergydecreasesandthestabilityof

asystemincreases

•  Equilibrium

•  stateofmaximumstability

•  Lowestenergy

•  Aprocessisspontaneousandcanperform

workonlywhenitismovingtoward

equilibrium

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ExergonicandEndergonicReac9onsinMetabolism

•  Freeenergychangesinreac9ons

•  Exergonicreac4on

•  proceedswithanetreleaseoffree

energyandisspontaneous

•  Resultsinlowerenergy,morestable

products

•  Endergonicreac4on

•  absorbsfreeenergyfromits

surroundingsandisnonspontaneous

•  Resultsinhigherenergy,lessstable

products

Energy

(a) Exergonic reaction: energy released

Progress of the reaction

Free

ene

rgy

Products

Amount of energy

released (∆G < 0)

Reactants

Energy

(b) Endergonic reaction: energy required

Progress of the reaction

Free

ene

rgy

Products

Amount of energy

required (∆G > 0)

Reactants

EquilibriumandMetabolism•  Closedsystems

•  eventuallyreachequilibriumandthen

donomorework

•  Cellsareopensystems

•  Therefore,notinequilibrium

•  Experiencingaconstantflowof

materials

•  Metabolismisneveratequilibrium

•  Adefiningfeatureoflife

•  Acatabolicpathwayinacellreleasesfree

energyinaseriesofreac9ons

(a) An isolated hydroelectric system

∆G < 0 ∆G = 0

(b) An open hydroelectric system ∆G < 0

∆G < 0 ∆G < 0

∆G < 0

(c) A multistep open hydroelectric system

TheStructureandHydrolysisofATP

Phosphate groups Ribose

Adenine

•  ATP(adenosinetriphosphate)

•  Energycurrencyofthecell

•  composedof

•  ribose(asugar)

•  adenine(anitrogenousbase)

•  threephosphategroups

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TheStructureandHydrolysisofATP

Inorganic phosphate

Energy

Adenosine triphosphate (ATP)

Adenosine diphosphate (ADP)

P P

P P P

P + +

H2O

i

•  Harves9ngpowerfromATP

•  Breakhighenergyphosphatebonds

•  Byhydrolysis

•  Energyreleasedwhenterminalphosphate

bondisbroken

•  Releaseofenergycomesfromchemical

changetostateoflowerfreeenergy

•  notfromthephosphatebondsthemselves

EnergyLight energy

ECOSYSTEM

Photosynthesis in chloroplasts

CO2 + H2O

Cellular respiration in mitochondria

Organic molecules+ O2

ATP powers most cellular work

Heat energy

ATP

•  Energyarrivesassunlight

•  Photosynthesis

•  Plantscapturesunlight

•  MakeorganicmoleculesandgeneratesO2

•  Carbsusedincellularrespira9on

•  Cellsuseenergystoredinorganicmolecules

•  toregenerateATP

•  Energyeventuallyleavesasheat

CatabolicPathwaysandProduc9onofATP

•  Thebreakdownoforganicmoleculesisexergonic

•  Aerobicrespira4on

•  ConsumesorganicmoleculesandO2andyieldsATP

•  Typicallyglucose

•  Fermenta4on

•  Par9aldegrada9onofsugarsthatoccurswithoutO2

•  Anaerobicrespira4on

•  similartoaerobicrespira9on

•  butusescompoundsotherthanO2asthefinalelectronacceptor

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•  Cellularrespira4on

•  includesbothaerobicandanaerobicrespira9onbutisoSenusedtoreferto

aerobicrespira9on

•  3of4macromoleculeclassesmaybeusedasfuel

•  carbohydrates,fats,andproteins

SummaryEqua4onforAerobicCellularRespira4on

C6H12O6+6O2→6CO2+6H2O+Energy(ATP+heat)

CellularRespira9on

ThePrincipleofRedox•  oxida9on-reduc9onreac9ons

•  Chemicalreac9onsthattransferelectronsbetweenreactantsarecalled

•  redoxreac4ons

•  Oxida4on

•  asubstanceloseselectrons

•  Reduc4on

•  asubstancegainselectron

•  OIL-RIG

becomes oxidized (loses electron)

becomes reduced (gains electron)

becomes oxidized

becomes reduced

NAD+andtheElectronTransportChain

•  Glucoseandotherorganicmolecules

•  Brokendowninaseriesofsteps

•  NAD+(nico9namideadeninedinucleo9de)

•  Electroncarrier

•  Transferselectronsfromorganiccompounds

•  Func9onsasanoxidizingagentduringcellularrespira9on

•  NADH

•  ReducedformofNAD+

•  representsstoredenergythatisusedtosynthesizeATP

Dehydrogenase

Dehydrogenase

Reduction of NAD+

Oxidation of NADH

2 e– + 2 H+ 2 e– +

H+

NAD+ + 2[H]

NADH

+

H+

H+

Nicotinamide (oxidized form)

Nicotinamide (reduced form)

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•  NADH

•  Deliverselectronstotheelectron

transportchain(ETC)

•  ETCpasseselectronsinaseriesofsteps

•  insteadofoneexplosivereac9on

•  Slow,controlledenergy

release

•  O2receiveselectronsfromtheETC

•  ASeranenergy-yieldingtumble

downthechain

•  Knownas“finalelectronacceptor”

•  Theenergyyieldedisusedto

regenerateATP

NAD+andtheElectronTransportChain

Free

ene

rgy,

G

Free

ene

rgy,

G

(a) Uncontrolled reaction

H2O

H2 + 1/2 O2

Explosive release of

heat and light energy

(b) Cellular respiration

Controlled release of energy for

synthesis of ATP

2 H+ + 2 e–

2 H + 1/2 O2

(from food via NADH)

ATP

ATP

ATP

1/2 O22 H+

2 e–

Electron transport

chain

H2O

TheStagesofCellularRespira9on:APreview

•  Cellularrespira9onhasthreestages:

1.   Glycolysis

•  Literally“sugarbreaking”

•  breaksdownglucoseintotwomoleculesofpyruvate

2.   Citricacidcycle

•  completesthebreakdownofglucose

•  AlsocalledKrebscycle

3.   Oxida4vephosphoryla4on

•  accountsformostoftheATPsynthesis

•  IncludesElectronTransportChain

Fig. 9-6-1

Substrate-level phosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electrons carried

via NADH

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Fig. 9-6-2

Mitochondrion

Substrate-level phosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electrons carried

via NADH

Substrate-level phosphorylation

ATP

Electrons carried via NADH and

FADH2

Citric acid cycle

Fig. 9-6-3

Mitochondrion

Substrate-level phosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electrons carried

via NADH

Substrate-level phosphorylation

ATP

Electrons carried via NADH and

FADH2

Oxidative phosphorylation

ATP

Citric acid cycle

Oxidative phosphorylation: electron transport

and chemiosmosis

•  Oxida4vephosphoryla4on

•  accountsforalmost90%oftheATPgeneratedbycellularrespira9on

•  32of36-38total

•  Substrate-levelphosphoryla4on

•  ATPformedinglycolysisandthecitricacidcycle

Enzyme

ADP

PSubstrate

Enzyme

ATP+

Product

Oxida9vePhosphoryla9on

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Glycolysis

•  Glycolysis

•  Breaksdownglucoseinto

twomoleculesofpyruvate

•  Occursinthecytoplasm

•  Twomajorphases:

•  Energyinvestment

phase

•  Energypayoffphase

Energy investment phase

Glucose

2 ADP + 2 P 2 ATP used

formed4 ATP

Energy payoff phase

4 ADP + 4 P

2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

2 Pyruvate + 2 H2O

2 Pyruvate + 2 H2OGlucoseNet

4 ATP formed – 2 ATP used 2 ATP

2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

IntermediateStep•  IfO2ispresent

•  pyruvateentersthe

mitochondrion

•  Twoperoriginalglucose

•  acetylCoAformedwhenPyruvate

addedtocoenzymeA

•  Asitcrossesthe

mitochondrial

membranes

•  YieldsfirstCO2wastes

•  ReducesaNAD+toNADH

•  Entersthecitricacidcycle

CYTOSOL MITOCHONDRION

NAD+ NADH + H+

2

1 3

Pyruvate

Transport protein

CO2Coenzyme A

Acetyl CoA

•  Citricacidcycle

•  AlsocalledtheKrebscycle

•  Occursinthemitochondrial

matrix

•  oxidizesorganicfuelderived

frompyruvate

•  generates1ATP,3NADH,

and1FADH2percycle

•  and2CO2

•  Twocyclesperoriginal

glucose!

Pyruvate

NAD+

NADH

+ H+Acetyl CoA

CO2

CoA

CoA

CoA

Citric acid cycle

FADH2

FAD

CO22

3

3 NAD+

+ 3 H+

ADP + P i

ATP

NADH

CitricAcidCycle

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•  Citricacidcycle

•  Eightsteps

•  Eachcatalyzedbyaspecificenzyme

•  AcetylgroupofacetylCoAjoinsthecyclebycombiningwithoxaloacetate

•  Formingcitrate

•  CoenzymeAreturnstointermediatestep

•  Thenextsevenstepsdecomposethecitratebacktooxaloacetate

•  Makestheprocessacycle

•  TheNADHandFADH2

•  Deliverelectronstotheelectrontransportchain

Pyruvate

NAD+

NADH+ H+

Acetyl CoA

CO2

CoA

CoA

CoA

Citric acid cycle

FADH2

FAD

CO22

3

3 NAD+

+ 3 H+

ADP + P i

ATP

NADH

CitricAcidCycle

Fig. 9-12-8

Acetyl CoACoA—SH

Citrate

H2O

IsocitrateNAD+

NADH+ H+

CO2

α-Keto- glutarate

CoA—SH

CO2NAD+

NADH+ H+Succinyl

CoA

CoA—SH

P iGTP GDP

ADP

ATP

SuccinateFAD

FADH2

Fumarate

Citric acid cycleH2O

Malate

Oxaloacetate

NADH+H+

NAD+

1

2

3

4

5

6

7

8

ElectronTransport•  Electrontransportchain

•  Ontheinnermembrane(cristae)

ofthemitochondrion

•  Mostlyinmul9proteincomplexes

•  Carriersalternatereducedandoxidized

states

•  astheyacceptanddonate

electrons

•  Electronbucketbrigade

•  Electrons

•  Dropinfreeenergyastheygo

downthechain

•  FinallypassedtoO2,formingH2O

NADH

NAD+2FADH2

2 FADMultiprotein complexesFAD

Fe•SFMN Fe•S

Q

Fe•S

Ι

Cyt b

ΙΙ

ΙΙΙ

Cyt c1

Cyt cCyt a

Cyt a3

IV

Free

ene

rgy

(G) r

elat

ive

to O

2 (kc

al/

mol

)

50

40

30

20

10 2(from NADH or FADH2)

0 2 H+ + 1/2 O2

H2O

e–

e–

e–

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•  Electrontransportchain

•  generatesnoATP(directly)

•  ButcreatesH+gradient

•  Concentratedinthe

intermembrane

space

•  breaksthelargefree-energy

dropfromglucosetoO2

•  intosmallerstepsthat

releaseenergyin

manageableamounts

ElectronTransportChain

Chemiosmosis:TheEnergy-CouplingMechanism•  H+intheintermembranespace

•  thenmovebackacrossthemembrane

•  Downconcentra9ongradient

•  passingthroughchannelsinATP

synthase

•  ATPsynthase

•  usestheexergonicflowofH+todrive

phosphoryla9onofATP

•  ThisisChemiosmosis

•  TheuseofenergyinaH+gradienttodrive

cellularwork

INTERMEMBRANE SPACE

Rotor

H+

Stator

Internal rod

Cata- lytic knob

ADP+P ATP

i

MITOCHONDRIAL MATRIX

Fig. 9-16

Protein complex of electron carriers

H+

H+H+

Cyt c

Q

Ι

ΙΙ

ΙΙΙ

ΙV

FADH2 FAD

NAD+NADH(carrying electrons from food)

Electron transport chain

2 H+ + 1/2O2 H2O

ADP + P i

Chemiosmosis

Oxidative phosphorylation

H+

H+

ATP synthase

ATP

21

PLAY

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AerobicRespira9onSummary

•  Energyflowsinthissequence:

glucose→NADH →electrontransportchain→proton-mo9veforce→ATP

•  About37%oftheenergyinaglucosemoleculeistransferredtoATPduring

cellularrespira9on

•  Makesabout38ATP

•  36net!(Actuallyabout30inEukaryotes)

•  Roughly3ATPperreducedelectroncarrier(NADH/FADH2eachwitha

pairofelectrons)

•  Inaddi9ontothoseATPformedbysubstratelevelphosphoryla9on

Fig. 9-17

Maximum per glucose: About 36 or 38 ATP

+ 2 ATP+ 2 ATP + about 32 or 34 ATP

Oxidative phosphorylation: electron transport

and chemiosmosis

Citric acid cycle

2 Acetyl CoA

Glycolysis

Glucose2

Pyruvate

2 NADH 2 NADH 6 NADH 2 FADH2

2 FADH2

2 NADHCYTOSOL Electron shuttles

span membrane

or

MITOCHONDRION

Fermenta9onandanaerobicrespira9on

•  Aerobiccellularrespira9onrequiresO2to

produceATP

•  Glycolysis

•  canproduceATPwithorwithoutO2

•  inaerobicoranaerobiccondi9ons

•  WithoutO2

•  Electrontransportchaincan’t

releaseelectrons

•  Systembacksupandshuts

down

•  Glycolysiscoupleswith

fermenta4onoranaerobic

respira4ontoproduceATP

NADH

NAD+2FADH2

2 FADMultiprotein complexesFAD

Fe•SFMN

Fe•SQ

Fe•S

Ι

Cyt b

ΙΙ

ΙΙΙ

Cyt c1

Cyt cCyt a

Cyt a3

IV

Free

ene

rgy

(G) r

elat

ive

to O

2 (kc

al/m

ol)

50

40

30

20

10 2(from NADH or FADH2)

0 2 H+ + 1/2 O2

H2O

e–

e–

e–

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•  Anaerobicrespira9on

•  usesETCwithanelectron

acceptorotherthanO2…

•  sulfate

•  Fermenta9on

•  usessubstratelevel

phosphoryla9onaSer

glycolysis

•  insteadofanelectron

transportchainto

generateATP

Fermenta9onandanaerobicrespira9on

TypesofFermenta9on•  Fermenta9on

•  Consistsofglycolysisplus

reac9onsthatregenerate

NAD+

•  Tobereusedby

glycolysis

•  Twocommontypes

•  alcoholfermenta9on

•  Plants,fungi,bacteria

•  lac9cacidfermenta9on

•  Animalsandafew

bacteriaandfungi

•  Alcoholfermenta4on

•  Pyruvateis

convertedtoethanol

intwosteps

•  firstreleasesCO2

•  Usedbyyeastinbrewing,

winemaking,andbaking

Fermenta9on

2 ADP + 2 P i 2 ATP

Glucose Glycolysis

2 Pyruvate

2 NADH2 NAD+

+ 2 H+CO2

2 Acetaldehyde2 Ethanol

(a) Alcohol fermentation

2

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•  Lac4cacidfermenta4on

•  PyruvateisreducedbyNADH

•  formslactateasanend

product

•  noreleaseofCO2

•  Usedbysomefungiandbacteria

tomakecheeseandyogurt

•  Humanmusclecells

•  usetogenerateATPwhenO2is

scarceorabsent

•  Earlyinstrenuousexercise

assugarcatabolism

outpacesoxygendelivery

Fermenta9onandanaerobicrespira9on

Glucose

2 ADP + 2 P i 2 ATP

Glycolysis

2 NAD+ 2 NADH+ 2 H+

2 Pyruvate

2 Lactate

(b) Lactic acid fermentation

Fermenta9onandAerobicRespira9onCompared

•  Bothprocesses

•  Useglycolysistooxidizeglucoseandotherorganicfuelstopyruvate

•  Havedifferentfinalelectronacceptors:

•  Fermenta9on

•  anorganicmolecule

•  pyruvateoracetaldehyde

•  AerobicCellularrespira9on

•  O2

•  Cellularrespira9on

•  Produces36(or30(38))ATPperglucosemolecule

•  Fermenta9on

•  Produces2(net)(4)ATPperglucosemolecule

•  Obligateanaerobes

•  carryoutfermenta9onoranaerobic

respira9on

•  cannotsurviveinthepresenceofO2

•  Faculta4veanaerobes

•  Yeastandmanybacteria

•  cansurviveusingeither

fermenta9onorcellular

respira9on

•  pyruvateisaforkinthemetabolic

road

•  thatleadstotwoalterna9ve

catabolicroutes

Fermenta9onandAnaerobicrespira9on

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Fig. 9-19

Glucose

Glycolysis

Pyruvate

CYTOSOL

No O2 present: Fermentation

O2 present: Aerobic cellular respiration

MITOCHONDRIONAcetyl CoAEthanol

or lactate

Citric acid cycle

TheVersa9lityofCatabolism

•  Catabolicpathways

•  funnelelectronsfrommanykindsoforganicmoleculesintocellular

respira9on

•  Glycolysis

•  acceptsawiderangeofcarbohydrates

•  Notjustglucoseorpolymersofglucose

•  Proteins

•  mustbedigestedtoaminoacids

•  aminoacidscanfeedglycolysisorthecitricacidcycle

•  Mustbedeaminatedfirst

•  Createsnitrogenouswastessuchasurea,uricacid,and

ammonia

•  Fatsdigestedto

•  glycerol(usedinglycolysis)

•  convertedtoG3P

•  faJyacids(usedingenera9ngacetylCoA)

•  FaJyacids

•  brokendownbybetaoxida4on

•  yield2-carbonfragments

•  becomesacetylCoA

•  AlsoyieldssomeNADHand

FADH2

•  Anoxidizedgramoffatproducesmorethan

twiceasmuchATPasanoxidizedgramof

carbohydrate

TheVersa9lityofCatabolism

Proteins Carbohydrates

Amino acids

Sugars

Fats

Glycerol Fatty acids

Glycolysis

Glucose

Glyceraldehyde-3-

Pyruvate

P

NH3

Acetyl CoA

Citric acid cycle

Oxidative phosphorylation

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Now You Should Know

1.  Explainingeneraltermshowredoxreac9onsareinvolvedinenergyexchanges

2.  Namethethreestagesofcellularrespira9on;foreach,statethe

regionoftheeukaryo9ccellwhereitoccursandtheproductsthatresult

3.  Ingeneralterms,explaintheroleoftheelectrontransportchainincellularrespira9on

4.  Explainwhereandhowtherespiratoryelectrontransportchaincreatesaprotongradient

5.  Dis9nguishbetweenfermenta9onandanaerobicrespira9on