Chapter 09 Cellular Respiration

Cellular Respiration: Harvesting of

Cellular Energy

Chapter 09

Learning objectivesLearning objectives• Describe energy flow in the biosphere according to Describe energy flow in the biosphere according to

the principle endergonic and exergonic reaction the principle endergonic and exergonic reaction cycles. cycles.

• Describe how energy is obtained through the redox Describe how energy is obtained through the redox reactions of cellular respiration in mitochondriareactions of cellular respiration in mitochondria

• Name the major input and output compounds for Name the major input and output compounds for glycolysis, transition, Krebs cycle and Electron glycolysis, transition, Krebs cycle and Electron Transport/ATP synthaseTransport/ATP synthase

• Explain how fermentation provides for ATP in the Explain how fermentation provides for ATP in the absence of oxygenabsence of oxygen

• Describe how the mitochondria provides for Describe how the mitochondria provides for synthesis of macromoleculessynthesis of macromolecules

• Compare and differentiate mitochondria and Compare and differentiate mitochondria and chloroplasts in terms of major reactants and prod. chloroplasts in terms of major reactants and prod.

2Chapter 09Respiration


OutlineOutline1.1. GlycolysisGlycolysis2.2. Transition ReactionTransition Reaction3.3. Citric Acid CycleCitric Acid Cycle4.4. Electron Transport SystemElectron Transport System5.5. FermentationFermentation6.6. Metabolic PoolMetabolic Pool

CatabolismCatabolism AnabolismAnabolism


Cellular RespirationCellular RespirationA 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 waterEnergy 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

Coenzymes NADCoenzymes NAD++ FAD deliver high energy FAD deliver high energy electrons to Oxidation-reduction chain in electrons to Oxidation-reduction chain in mitochondrial membranemitochondrial membrane


Summary Equation Summary Equation

LEO says GER

Loss of Electrons = OxidationGain of Electrons = Reduction

Theoverallbreakdownofglucoseissummarizedas:

“Metabolic Water”

6Chapter 09RespirationCoenzymes:Coenzymes:

NADNAD++ and FAD and FAD

1. NAD1. NAD++ (nicotinamide adenine dinucleotide) (nicotinamide adenine dinucleotide) 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 NAD(Each NAD++ molecule used over and over again) molecule used over and over again)

2. FAD (flavin adenine dinucleotide)2. FAD (flavin adenine dinucleotide)Sometimes 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


NADNAD++ Cycle Cycle

Electron (1 neg. charge)Lost, therefore NAD Becomes postive, thereforeOxidized

NAD loses charge, i.e. gains electron, therefore Reduced

8Chapter 09RespirationCellular Respiration:Cellular Respiration:

Overview of 4 PhasesOverview of 4 Phases1. Glycolysis: 1. Glycolysis: glucose to pyruvateglucose to pyruvate

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

2. Transition / Preparatory reaction: 2. Transition / Preparatory reaction: pruvate to acetyl-CoApruvate to acetyl-CoA 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

3. Citric acid cycle: 3. Citric acid cycle: electrons removed from acetyl groups (oxid.)electrons removed from acetyl groups (oxid.) 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

4. Electron transport chain: 4. Electron transport chain: energy extracted from electrons. energy extracted from electrons. Extracts energy from NADH & FADHExtracts energy from NADH & FADH22 Produces 32 or 34 molecules of ATPProduces 32 or 34 molecules of ATP

Pyruvate converted to acetyl-CoA and enters mitochondria


Glucose Breakdown:Glucose Breakdown:Visual Overview of 4 Visual Overview of 4 PhasesPhases

TransitionReaction

1.

2.

3. 4.

Fig. 9.6 p167

10Chapter 09RespirationGlucose Breakdown:Glucose Breakdown:

1. Glycolysis1. Glycolysis

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+ + (NAD reduce, glucose oxidized)(NAD reduce, glucose oxidized)

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 Both G3Ps converted to pyruvatespyruvates

Glycolysis:In the cytoplasm, glucose is broken down to G3P then pyruvate with a net yeild of 2ATP.

11Chapter 09RespirationSubstrate-level Substrate-level

PhosphorylationPhosphorylation

Substrateisaglycolysisintermediatesubstrate.


1 Glycolysis1 Glycolysis

TransitionReaction

1.

2

Acetyl-CoA

2NADH


GlycolysisGlycolysisGlycolysis: Ten enzymatic steps

G3PGlyceraldehyde-3-phosphate

2ATP input

4ATP output


2.The Preparatory (Prep) Reaction2.The Preparatory (Prep) Reaction

End product of glycolysis, End product of glycolysis, pyruvate,pyruvate, enters enters the mitochondrial the mitochondrial matrixmatrix

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

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

Electrons picked up (as hydrogen atom) by Electrons picked up (as hydrogen atom) by NADNAD+ (reduction)+ (reduction)

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

Preparatory step:Pyruvates are converted to acetyl-CoA, NAD is reduced, carbon dioxide is released. All this occurs on the outside membrane of the mitochondria.


Mitochondrion:Mitochondrion:Structure & Structure & FunctionFunction

a.

b.c.e.

d.

Mitochondria.


As pyruvate is oxidized – NAD+ is reduced

TransitionReaction

2.

2.

Fig. 9.10 p169


3. The Citric Acid Cycle3. The Citric Acid Cycle

A.K.A. Krebs cycleA.K.A. Krebs cycleOccurs in Occurs in matrixmatrix of mitochondria of mitochondriaBoth acetyl (CBoth acetyl (C22) groups received from the ) groups received from the

preparatory reaction:preparatory reaction:Acetyl (CAcetyl (C22) group transferred to oxaloacetate ) group transferred to oxaloacetate (C(C22) to make citrate (C) to make citrate (C66))

Each acetyl oxidized to two COEach acetyl oxidized to two CO22 molecules moleculesRemaining 4 carbons from oxaloacetate Remaining 4 carbons from oxaloacetate converted restart the cycle. (thus “cyclic”)converted restart the cycle. (thus “cyclic”)

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

Krebs cycle:Within the mitochondrial matrix acetly-CoA (2C) plus oxaloacetate (4C) goes to citrate (6C) then through 4 more steps back to oxaloacetate. At each step an high energy electron is tranferred to NAD or FADH. Carbon dioxide is released at two of these steps, and the the cycle runs twice for each molecule of glucose (ie. Two acetyl-CoA produced from glycolysis)

Therefore the yield is…….

Respiration


Citric Acid Cycle

3.

The Citric Acid CycleThe Citric Acid Cycle





Thisreactionsequencecyclestwice:

Whatisthenetyieldofhighenergyelectroncarriers?

WhatisthenetyieldofATP?


Citric Acid Citric Acid Cycle:Cycle:Balance SheetBalance Sheet

Net yield


4. Electron Transport Chain4. Electron Transport Chain

• Location:Location: Eukaryotes: Eukaryotes: cristae of the mitochondriacristae of the mitochondria Aerobic Prokaryotes: plasma membraneAerobic Prokaryotes: plasma membrane

4.


Energy from electronsEnergy from electrons

• Series of carrier molecules pass energy rich Series of carrier molecules pass energy rich electrons along redox chain in membrane of electrons along redox chain in membrane of the cristae. (cytochromes)the cristae. (cytochromes) Cytochromes Cytochromes are respiratory molecules withare respiratory molecules with complex carbon rings with metal atoms in complex carbon rings with metal atoms in center. (recall shape of chlorophyll)center. (recall shape of chlorophyll)

• Receives electrons from NADH & FADHReceives electrons from NADH & FADH22

• Produce ATP by oxidative phosphorylationProduce ATP by oxidative phosphorylation


Electron Transport ChainElectron Transport ChainHigh energy electrons fromCitric acid cycle. Transferred To ETC by NADH and FADH2

WherearetheseenzymesAndco-enzymeslocated?

Fig. 9.13 p173


Organization of CristaeOrganization of Cristae

E.T.C.Oxidative Phosphorylation

Step 5. Oxidative Phosphorylation

ATP is formed via Oxidative phosphorylation:Electrons from Krebs cycle, via NADH and FADH2 ,are transferred to an electron transport chain in the cristae (inner membrane) where their energy is used to drive phosporylation of ADP to form ATP.

(Fig.9.15 p175)

28Chapter 09RespirationGlucose Catabolism:Glucose Catabolism:

Overall Energy YieldOverall Energy Yield

Net yield per glucose:Net yield per glucose:From glycolysis – 2 ATPFrom glycolysis – 2 ATPFrom citric acid cycle – 2 ATPFrom citric acid cycle – 2 ATPFrom electron transport chain – 28 ATPFrom electron transport chain – 28 ATP

Energy content:Energy content:Reactant (glucose) 686 kcalReactant (glucose) 686 kcalEnergy yield (36 ATP) 263 kcalEnergy yield (36 ATP) 263 kcalEfficiency 39%; balance is heatEfficiency 39%; balance is heat


Overall Energy Overall Energy YieldedYieldedper Glucose Moleculeper Glucose Molecule (Fig.9.16 p176)


Variable yield of ATPVariable yield of ATP

Only 2 H+ per FADH2

*

Intramembrane space

Matrix

E.T.C

Part of the source

Of ‘metabolic’ water


Oxygen and fate of electronsOxygen and fate of electrons

The fate of the hydrogens:The fate of the hydrogens:Hydrogens from NADH deliver enough energy Hydrogens from NADH deliver enough energy to make 2.5 ATPsto make 2.5 ATPs

Those from FADHThose from FADH22 have only enough for 1.5 have only enough for 1.5 ATPsATPs

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

NAD+ and FADH return to the Krebs cycle.NAD+ and FADH return to the Krebs cycle. 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+ +

(Fermentation)(Fermentation)

A byproduct of oxidative phosphorylation is the production of water as Hydrogen combines with oxygen.

If oxygen is absent, fermentation takes place.


FermentationFermentation

Oxygen required here

X

LactateNADH

NAD+


FermentationFermentation (Fig.9.17 p178)


Fermentation (1)Fermentation (1)

When oxygen limited:When oxygen limited:Spent hydrogens have no acceptorSpent hydrogens have no acceptorNADH can’t recycle back to NADNADH can’t recycle back to NAD++

Glycolysis stops because NADGlycolysis stops because NAD++ required requiredFermentation:Fermentation:

““Anaerobic” pathwayAnaerobic” pathwayCan provide rapid burst of ATPCan provide rapid burst of ATPProvides NADProvides NAD++ for glycolysis for glycolysisNADH combines with pyruvate to yield NADNADH combines with pyruvate to yield NAD++

35Chapter 09RespirationMetabolic Pool:Metabolic Pool:

Catabolism (1)Catabolism (1)

Foods:Foods:Sources of energy rich moleculesSources of energy rich moleculesCarbohydrates, 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 intermediates:pathways as intermediates:

11stst choice: choice: CarbohydratesCarbohydrates Converted into glucoseConverted into glucose Processed as aboveProcessed as above


Catabolism (2)Catabolism (2)Breakdown products enter into respiratory pathways Breakdown products enter into respiratory pathways

as intermediates (cont.) as intermediates (cont.) 22ndnd choice, Fats: choice, Fats:

- Breakdown of fats produces glycerol and fatty - Breakdown of fats produces glycerol and fatty acids. acids. - Glycerol enters the glycolysis pathway, Fatty - Glycerol enters the glycolysis pathway, Fatty acids are converted to actetyl-CoA and enter acids are converted to actetyl-CoA and enter Krebs cycle. Krebs cycle.

33rdrd choice, Proteins: choice, Proteins: Deaminated in the liver and can be converted to Deaminated in the liver and can be converted to

pyruvate, or acetyl-CoA, or one of the other Krebs pyruvate, or acetyl-CoA, or one of the other Krebs cycle intermediates. cycle intermediates.

Removed amino group (NHRemoved amino group (NH22)is converted to ammonia )is converted to ammonia (NH(NH33), and then to less reactive urea to be removed ), and then to less reactive urea to be removed by the kidneys.by the kidneys.

Other sources of energy: If glucose is not available, the breakdown products of fats and proteins can also be introduced into Krebs cycle at various places.


Anabolism (1)Anabolism (1)All metabolic reactions part of metabolic poolAll metabolic reactions part of metabolic poolIntermediates from respiratory pathways can be Intermediates from respiratory pathways can be

used for anabolismused for anabolismAnabolism (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

Krebs cycle intermediates are used to synthesize various components of macromolecues (fats, proteins and nucleic acidsGlycero-3-phosphate (G3P) and acetyl-CoA are used to form triglycerides. Intermediates of Krebs cycle are used to form 11 of the 20 amino acids. The other 9 must be obtained from dietary souces. Example: many grains lack lysine, but beans (legumes) are high in lysine, therefore the consumption of rice and beans together constitutes a “complete protein” source.


The Metabolic Pool ConceptThe Metabolic Pool Concept

C3

C2

C3

C2

Catabolic

Anabolic

(Fig.9.19 p180)

Fate of LactateFate of Lactate40Chapter 09

Respiration


ReviewReview

GlycolysisGlycolysisTransition ReactionTransition ReactionCitric Acid CycleCitric Acid CycleElectron Transport SystemElectron Transport SystemFermentationFermentationMetabolic PoolMetabolic Pool

CatabolismCatabolismAnabolismAnabolism

In cytoplasm: glucose 2 pyruvates, 2NADH, 2ATP

Pyruvates to acetyl-CoA on membrane of mitochondria. Yields 2NADH

2 acetyl-CoA cycled through 4 steps yields 4CO2, 6NADH, 2FADH2, 2ATP

Coupled to a proton pump, 3 protons pumped per cycle, 1 ATP per protonTherefore NADH yields 30 ATP

Can continue the production of ATP in the absence of oxygen. Pyruvate is reduced to lactic acid.

Triglycerides and amino acids cycle in and out of glycolysis and the Krebs cycle.

Education

Chapter 09 Cellular Respiration