62744282 Cellular Respiration (1)

Cellular Respiration

Chapter 08

2Cellular ResCellular Respirationpiration

OutlineOutline

GlycolysisGlycolysis

Transition ReactionTransition Reaction

Citric Acid CycleCitric Acid Cycle

Electron Transport SystemElectron Transport System

FermentationFermentation

Metabolic PoolMetabolic Pool

CatabolismCatabolism

AnabolismAnabolism


Cellular RespirationCellular Respiration

A cellular process that requires oxygen and A cellular process that requires oxygen and gives off carbon dioxidegives off carbon dioxide

Usually involves breakdown of glucose to Usually involves breakdown of glucose to carbon dioxide and watercarbon dioxide and water

Energy extracted from glucose molecule:Energy extracted from glucose molecule:

Released step-wiseReleased step-wise

Allows ATP to be produced efficientlyAllows ATP to be produced efficiently

Oxidation-reduction enzymes include NADOxidation-reduction enzymes include NAD++ and FAD as coenzymesand FAD as coenzymes

4Glucose Breakdown:Summary Reaction


NADNAD++ and FAD and FAD

NADNAD++ (nicotinamide adenine dinucleotide) (nicotinamide adenine dinucleotide)Called a coenzyme of oxidation-reduction it Called a coenzyme of oxidation-reduction it can can Oxidize a metabolite by accepting electronsOxidize a metabolite by accepting electrons Reduce a metabolite by giving up electronsReduce a metabolite by giving up electrons

Each NADEach NAD++ molecule used over and over again molecule used over and over again

FAD (flavin adenine dinucleotide)FAD (flavin adenine dinucleotide)Also a coenzyme of oxidation-reductionAlso a coenzyme of oxidation-reductionSometimes used instead of NADSometimes used instead of NAD++

Accepts two electrons and two hydrogen ions Accepts two electrons and two hydrogen ions (H(H++) to become FADH) to become FADH22

6NAD+ Cycle

7Cellular ResCellular RespirationpirationCellular Respiration:Cellular Respiration:

Overview of 4 PhasesOverview of 4 PhasesGlycolysis:Glycolysis:

Occurs in cytoplasmOccurs in cytoplasm Glucose broken down to two molecules of pyruvateGlucose broken down to two molecules of pyruvate ATP is formedATP is formed

Transition reaction:Transition reaction: Both pyruvates are oxidizedBoth pyruvates are oxidized Electron energy is stored in NADHElectron energy is stored in NADH Two carbons are released as COTwo carbons are released as CO22

Citric acid cycle:Citric acid cycle: Electron energy is stored in NADH and FADHElectron energy is stored in NADH and FADH22 ATP is formedATP is formed Four carbons are released as COFour carbons are released as CO22

Electron transport chain:Electron transport chain: Extracts energy from NADH & FADHExtracts energy from NADH & FADH22 Produces 32 or 34 molecules of ATPProduces 32 or 34 molecules of ATP

8Glucose Breakdown:Overview of 4

Phases

9Cellular ResCellular RespirationpirationGlucose Breakdown:Glucose Breakdown:


Occurs in cytoplasm outside mitochondriaOccurs in cytoplasm outside mitochondriaEnergy Investment Steps:Energy Investment Steps:

Two ATP are used to activate glucoseTwo ATP are used to activate glucoseGlucose splits into two G3P moleculesGlucose splits into two G3P molecules

Energy Harvesting Steps:Energy Harvesting Steps:Two electrons (as hydrogen atoms) are picked Two electrons (as hydrogen atoms) are picked up by two NADup by two NAD++

Four ATP produced by substrate-level Four ATP produced by substrate-level phosphorylationphosphorylation

Net gain of two ATPNet gain of two ATPBoth G3Ps converted to pyruvatesBoth G3Ps converted to pyruvates

10Glycolysis:The Balance

Sheet

11Substrate-level Phosphorylation

12Glycolysis

13Glycolysis


The Preparatory (Prep) ReactionThe Preparatory (Prep) Reaction

End product of glycolysis, pyruvate, enters End product of glycolysis, pyruvate, enters the mitochondrial matrixthe mitochondrial matrix

Pyruvate converted to 2-carbon acetyl groupPyruvate converted to 2-carbon acetyl group

Attached to Coenzyme A to form acetyl-CoAAttached to Coenzyme A to form acetyl-CoA

Electron picked up (as hydrogen atom) by Electron picked up (as hydrogen atom) by NADNAD++

COCO22 released, and transported out of released, and transported out of mitochondria into the cytoplasmmitochondria into the cytoplasm

15Mitochondrion:Structure &

Function

16Preparatory Reaction


The Citric Acid CycleThe Citric Acid Cycle

A.K.A. Krebs cycleA.K.A. Krebs cycleOccurs in matrix of mitochondriaOccurs in matrix of mitochondria

Both acetyl (CBoth acetyl (C22) groups received from the ) groups received from the preparatory reaction:preparatory reaction: Join with an enzyme CoA molecule to make acetyl-Join with an enzyme CoA molecule to make acetyl-

CoACoA Acetyl (CAcetyl (C22) group transferred to oxaloacetate (C) group transferred to oxaloacetate (C22) to ) to

make citrate (Cmake citrate (C66)) Each acetyl oxidized to two COEach acetyl oxidized to two CO22 molecules molecules Remaining 4 carbons from oxaloacetate converted Remaining 4 carbons from oxaloacetate converted

back to oxaloacetate (thus “cyclic”)back to oxaloacetate (thus “cyclic”)

NADH, FADHNADH, FADH22 capture energy rich electrons capture energy rich electronsATP formed by substrate-level phosphorylationATP formed by substrate-level phosphorylation

18The Citric Acid Cycle

19Citric Acid Cycle:Balance Sheet


Electron Transport ChainElectron Transport Chain

Location:Location:Eukaryotes: cristae of the mitochondriaEukaryotes: cristae of the mitochondriaAerobic Prokaryotes: plasma membraneAerobic Prokaryotes: plasma membrane

Series of carrier molecules:Series of carrier molecules:Pass energy rich electrons alongPass energy rich electrons alongComplex arrays of protein and cytochromesComplex arrays of protein and cytochromes Cytochromes are respiratory moleculesCytochromes are respiratory molecules Complex carbon rings with metal atoms in Complex carbon rings with metal atoms in centercenter

Receives electrons from NADH & FADHReceives electrons from NADH & FADH22

Produce ATP by oxidative phosphorylationProduce ATP by oxidative phosphorylation


Electron Transport ChainElectron Transport Chain

The fate of the hydrogens:The fate of the hydrogens:Hydrogens from NADH deliver enough energy Hydrogens from NADH deliver enough energy to make 3 ATPsto make 3 ATPs

Those from FADHThose from FADH22 have only enough for 2 have only enough for 2 ATPsATPs

““Spent” hydrogens combine with oxygenSpent” hydrogens combine with oxygenRecycling of coenzymes increases efficiencyRecycling of coenzymes increases efficiency

Once NADH delivers hydrogens, it returns (as Once NADH delivers hydrogens, it returns (as NADNAD++) to pick up more hydrogens) to pick up more hydrogens

However, hydrogens must be combined with However, hydrogens must be combined with oxygen to make wateroxygen to make water

If OIf O22 not present, NADH cannot release H not present, NADH cannot release HNo longer recycled back to NADNo longer recycled back to NAD++

22Electron Transport Chain

23Organization of Cristae

24Cellular ResCellular RespirationpirationGlucose Catabolism:Glucose Catabolism:

Overall Energy YieldOverall Energy Yield

Net yield per glucose:Net yield per glucose:

From glycolysis – 2 ATPFrom glycolysis – 2 ATP

From citric acid cycle – 2 ATPFrom citric acid cycle – 2 ATP

From electron transport chain – 32 ATPFrom electron transport chain – 32 ATP

Energy content:Energy content:

Reactant (glucose) 686 kcalReactant (glucose) 686 kcal

Energy yield (36 ATP) 263 kcalEnergy yield (36 ATP) 263 kcal

Efficiency 39%; balance is waste heatEfficiency 39%; balance is waste heat

25Overall Energy Yieldedper Glucose Molecule


Fermentation (1)Fermentation (1)

When oxygen limited:When oxygen limited:Spent hydrogens have no acceptorSpent hydrogens have no acceptor

NADH can’t recycle back to NADNADH can’t recycle back to NAD++

Glycolysis stops because NADGlycolysis stops because NAD++ required required

Fermentation:Fermentation:““Anaerobic” pathwayAnaerobic” pathway

Can provide rapid burst of ATPCan provide rapid burst of ATP

Provides NADProvides NAD++ for glycolysis for glycolysis

NADH combines with pyruvate to yield NADNADH combines with pyruvate to yield NAD++

27Fermentation


Fermentation (2)Fermentation (2)

Pyruvate reduced by NADH to:Pyruvate reduced by NADH to:LactateLactate Animals & some bacteriaAnimals & some bacteria Cheese & yogurt; sauerkrautCheese & yogurt; sauerkraut

Ethanol & carbon dioxideEthanol & carbon dioxide YeastsYeasts Bread and alcoholic beveragesBread and alcoholic beverages

Allows glycolysis to proceed faster than OAllows glycolysis to proceed faster than O22 can be can be obtainedobtainedAnaerobic exerciseAnaerobic exerciseLactic acid accumulatesLactic acid accumulatesCauses cramping and oxygen debtCauses cramping and oxygen debt

When OWhen O22 restored, lactate broken down to restored, lactate broken down to acetyl-CoA and metabolizedacetyl-CoA and metabolized

29Products of Fermentation

30Efficiency of Fermentation

InLineFigure143

31Cellular ResCellular RespirationpirationMetabolic Pool:Metabolic Pool:

Catabolism (1)Catabolism (1)

Foods:Foods:Sources of energy rich moleculesSources of energy rich molecules

Carbohydrates, fats, and proteinsCarbohydrates, fats, and proteins

Catabolism (breakdown side of metabolism)Catabolism (breakdown side of metabolism)

Breakdown products enter into respiratory Breakdown products enter into respiratory pathways as intermediatespathways as intermediatesCarbohydratesCarbohydrates

Converted into glucoseConverted into glucose

Processed as aboveProcessed as above

32The Metabolic Pool Concept


Catabolism (2)Catabolism (2)

Breakdown products enter into respiratory Breakdown products enter into respiratory pathways as intermediates (cont.)pathways as intermediates (cont.)ProteinsProteins Broken into amino acids (AAs)Broken into amino acids (AAs) Some AAs used to make other proteinsSome AAs used to make other proteins Excess AAs deaminated (NHExcess AAs deaminated (NH22 removed) in liver removed) in liver

Results in poisonous ammonia (NHResults in poisonous ammonia (NH33)) Quickly converted to ureaQuickly converted to urea

Different R-groups from AAs processed Different R-groups from AAs processed differentlydifferently Fragments enter respiratory pathways at many Fragments enter respiratory pathways at many different pointsdifferent points


Anabolism (1)Anabolism (1)

All metabolic reactions part of metabolic poolAll metabolic reactions part of metabolic pool

Intermediates from respiratory pathways can be Intermediates from respiratory pathways can be used for anabolismused for anabolism

Anabolism (build-up side of metabolism):Anabolism (build-up side of metabolism): Carbs:Carbs: Start with acetyl-CoAStart with acetyl-CoA

Basically reverses glycolysis (but different pathway)Basically reverses glycolysis (but different pathway)

FatsFats G3P converted to glycerolG3P converted to glycerol

Acetyls connected in pairs to form fatty acidsAcetyls connected in pairs to form fatty acids

Note – dietary carbohydrate RARELY converted to fat in Note – dietary carbohydrate RARELY converted to fat in humans!humans!


Anabolism (2)Anabolism (2)

Anabolism (cont.):Anabolism (cont.):Proteins:Proteins:Made up of combinations of 20 different amino Made up of combinations of 20 different amino acidsacids Some amino acids (11) can be synthesized from Some amino acids (11) can be synthesized from respiratory intermediatesrespiratory intermediates organic acids in citric acid cycle can make amino organic acids in citric acid cycle can make amino

acidsacids Add NHAdd NH2 2 – transamination– transamination

However, other amino acids (9) cannot be However, other amino acids (9) cannot be synthesized by humanssynthesized by humans Essential amino acidsEssential amino acids Must be present in diet or dieMust be present in diet or die


ReviewReview


Transition ReactionTransition Reaction

Citric Acid CycleCitric Acid Cycle

Electron Transport SystemElectron Transport System

FermentationFermentation

Metabolic PoolMetabolic Pool

CatabolismCatabolism

AnabolismAnabolism

Cellular Respiration

Ending Slide Chapter 08

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62744282 Cellular Respiration (1)