chapter 9 complete
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Chapter 9Chapter 9Pathways that Harvest Chemical Pathways that Harvest Chemical
EnergyEnergy
Main Fuel Molecule: GlucoseMain Fuel Molecule: Glucose
Fuels: Molecules whose stored energy Fuels: Molecules whose stored energy can be released for use.can be released for use.
The most common fuel in organisms is The most common fuel in organisms is glucose. Other molecules are first glucose. Other molecules are first converted into glucose or other converted into glucose or other intermediate compounds.intermediate compounds.
Burning or metabolism of glucose:Burning or metabolism of glucose:
Glucose metabolism pathway traps the Glucose metabolism pathway traps the free energy in ATP:free energy in ATP:
How is Glucose Used to Make EnergyHow is Glucose Used to Make Energy
energyfreeOHCOOOHC 2226126 666
ATPenergyfreePADP i
How is Glucose Used to Make EnergyHow is Glucose Used to Make Energy
ΔΔGG is the change in free energy is the change in free energy ΔΔGG from from complete combustion complete combustion of of
glucose glucose = –686 kcal/mol= –686 kcal/molHighly exergonic; drives endergonic Highly exergonic; drives endergonic
formation of many ATP molecules.formation of many ATP molecules.
Three metabolic pathways are involved in Three metabolic pathways are involved in harvesting the energy of glucose:harvesting the energy of glucose:
GlycolysisGlycolysis: : glucose is converted to glucose is converted to pyruvatepyruvate
Cellular respirationCellular respiration: aerobic and : aerobic and converts pyruvate into converts pyruvate into HH22O, COO, CO22, and ATP, and ATP
FermentationFermentation: anaerobic and converts : anaerobic and converts pyruvate into lactic acid or pyruvate into lactic acid or ethanol, COethanol, CO22,, and ATPand ATP
The Big PictureThe Big PictureIf OIf O22 is present (aerobic): is present (aerobic):
Glycolysis is followed by three Glycolysis is followed by three pathways of cellular pathways of cellular respiration:respiration:• Pyruvate oxidationPyruvate oxidation• Citric acid cycleCitric acid cycle• Electron transport chainElectron transport chain
If OIf O22 is not present (anaerobic): is not present (anaerobic):
Pyruvate from glycolysis is Pyruvate from glycolysis is metabolized by fermentation.metabolized by fermentation.
Redox ReactionsRedox ReactionsRedox reactions: Redox reactions: One substance transfers One substance transfers
electrons to another substanceelectrons to another substanceReduction:Reduction: Gain of one or more electrons Gain of one or more electrons
by an atom, ion, or moleculeby an atom, ion, or moleculeOxidation:Oxidation: Loss of one or more electrons Loss of one or more electrons
Also occurs if Also occurs if hydrogenhydrogen atomsatoms are gained or are gained or lost (H = Hlost (H = H++ + e + e--))
Redox reactionsRedox reactionsOxidation and reduction Oxidation and reduction always occur togetheralways occur together..
The reactant that The reactant that becomes reduced is the becomes reduced is the oxidizing agentoxidizing agent..
The reactant that The reactant that becomes oxidized is the becomes oxidized is the reducing agentreducing agent..
Redox Reactions and GlucoseRedox Reactions and GlucoseIn glucose combustion, In glucose combustion, glucose is the reducing glucose is the reducing agent, Oagent, O22 is the oxidizing is the oxidizing agent.agent.
Energy is transferred in a Energy is transferred in a redox reaction.redox reaction.
Energy in the reducing agent Energy in the reducing agent (glucose) is transferred to (glucose) is transferred to the reduced product.the reduced product.
Electron CarriersElectron CarriersExamples: NAD, Examples: NAD,
FADH2, NADPHFADH2, NADPH
Coenzyme Coenzyme NADNAD++ is a is a key electron carrier key electron carrier in redox reactions.in redox reactions.
Two forms:Two forms:NADNAD++ (oxidized) (oxidized)NADH (reduced)NADH (reduced)
Complete vs. Incomplete Complete vs. Incomplete Oxidation of GlucoseOxidation of Glucose
Complete Oxidation
Incomplete Oxidation
The five metabolic pathways occur The five metabolic pathways occur in different parts of the cell.in different parts of the cell.
GlycolysisGlycolysis
Takes place in the cytosolTakes place in the cytosolConverts glucose into pyruvateConverts glucose into pyruvateProduces a small amount of energyProduces a small amount of energyGenerates no COGenerates no CO22
GlycolysisGlycolysisInvolves Involves tenten enzyme-catalyzed reactions. enzyme-catalyzed reactions.Energy-investing reactionsEnergy-investing reactions: Require ATP: Require ATPEnergy-harvesting reactionsEnergy-harvesting reactions: Yield NADH and ATP.: Yield NADH and ATP.
Results (net per glucose):Results (net per glucose):2 molecules of pyruvate2 molecules of pyruvate2 molecules of ATP2 molecules of ATP2 molecules of NADH2 molecules of NADH
““Energy Investing” Energy Investing” Steps of GlycolysisSteps of Glycolysis
So what is a kinase?So what is a kinase?
““Energy Harvesting” Energy Harvesting” Steps of GlycolysisSteps of Glycolysis
Substrate Level PhosphorylationSubstrate Level Phosphorylation
Enzyme-catalyzed transfer of a phosphate group Enzyme-catalyzed transfer of a phosphate group from a donor to ADP to form ATP is called from a donor to ADP to form ATP is called substrate-level phosphorylation.substrate-level phosphorylation.
Phosphorylation: addition of a phosphate group.Phosphorylation: addition of a phosphate group.
Anaerobic ConditionsAnaerobic ConditionsWithout OWithout O22, ATP can be produced by , ATP can be produced by
glycolysis and fermentation.glycolysis and fermentation.
Fermentation occurs in the cytosol, to Fermentation occurs in the cytosol, to regenerate NADregenerate NAD++. .
Pyruvate from glycolysis is reduced by Pyruvate from glycolysis is reduced by NADH + HNADH + H+.+.
Lactic Acid FermentationLactic Acid Fermentation• Occurs in Occurs in
microorganisms, microorganisms, some muscle cellssome muscle cells
• Pyruvate is the final Pyruvate is the final electron acceptorelectron acceptor
• Lactate is the Lactate is the product and can product and can build upbuild up
Alcohol FermentationAlcohol Fermentation• Requires two Requires two
enzymes to enzymes to metabolize pyruvate metabolize pyruvate to ethanolto ethanol
• Acetaldehyde is Acetaldehyde is reduced by NADH + reduced by NADH + HH++, producing NAD, producing NAD++ and glycolysis and glycolysis continuescontinues
Summary of Anaerobic Summary of Anaerobic Respiration Respiration
Cellular respiration yields more energy Cellular respiration yields more energy than fermentation per glucose than fermentation per glucose molecule.molecule.
• Glycolysis plus fermentation = 2 ATPGlycolysis plus fermentation = 2 ATP• Glycolysis plus cellular respiration = 32 Glycolysis plus cellular respiration = 32
ATPATP• So why do it?So why do it?
Aerobic Respiration: Pyruvate Oxidation Aerobic Respiration: Pyruvate Oxidation
Links Links glycolysisglycolysis and the and the citric acid cyclecitric acid cycle; ; occurs in the occurs in the mitochondrial matrixmitochondrial matrix
Pyruvate is oxidized to acetate and COPyruvate is oxidized to acetate and CO22 is is releasedreleased
NADNAD++ is reduced to NADH, capturing energy is reduced to NADH, capturing energySome energy is stored by combining acetate Some energy is stored by combining acetate
and Coenzyme A (CoA) to form acetyl CoA and Coenzyme A (CoA) to form acetyl CoA
Pyruvate OxidationPyruvate Oxidation
Per Glucose:2 NADH2CO2
2 Acetyl-CoA
Citric Acid CycleCitric Acid Cycle
InputsInputs:: acetyl CoA, water and electron acetyl CoA, water and electron carriers NADcarriers NAD++, FAD, and GDP, FAD, and GDP
Energy released is captured by Energy released is captured by ADPADP and and electron carriers electron carriers NADNAD++, FAD, and GDP, FAD, and GDP
OutputsOutputs:: CO CO22, reduced electron carriers, , reduced electron carriers, and ATP (really GTP)and ATP (really GTP)
Citric Acid CycleCitric Acid Cycle
The citric acid cycle is in steady state: The citric acid cycle is in steady state: The concentrations of the The concentrations of the intermediates don’t change.intermediates don’t change.
The cycle continues when starting The cycle continues when starting materials are available:materials are available:
• Acetyl CoAAcetyl CoA• Reoxidized electron carriersReoxidized electron carriers
Citric Acid CycleCitric Acid Cycle
Per Glucose:6 NADH2 FADH2
4 CO2
2 ATP
Complete Oxidation of Complete Oxidation of GlucoseGlucose
Recycle Electron CarriersRecycle Electron Carriers
The electron carriers that are reduced The electron carriers that are reduced during the citric acid cycle must be during the citric acid cycle must be reoxidizedreoxidized to take part in the cycle to take part in the cycle again.again.
Fermentation—if no OFermentation—if no O22 is present is present
Oxidative phosphorylationOxidative phosphorylation—O—O22 is present is present
Oxidative PhosphorylationOxidative Phosphorylation
Oxidative phosphorylation: ATP is Oxidative phosphorylation: ATP is synthesized by reoxidation of electron synthesized by reoxidation of electron carriers in the presence of Ocarriers in the presence of O22. .
Two stages:Two stages:• Electron transportElectron transport• Chemiosmosis Chemiosmosis
Electron Transport Chain Electron Transport Chain (ETC)(ETC)
Electrons from Electrons from NADH and FADHNADH and FADH22 pass pass through the respiratory chain of through the respiratory chain of membrane-associated carriers.membrane-associated carriers.Electron flow results in a Electron flow results in a proton proton concentrationconcentration (Membrane Potential) (Membrane Potential) gradient in mitochondria.gradient in mitochondria.
ETCETC
The respiratory chain is located in the The respiratory chain is located in the inner mitochondrial membrane inner mitochondrial membrane (cristae)(cristae)..
Energy is released as electrons are Energy is released as electrons are passed between carriers.passed between carriers.
Examples: protein complexes I, II, III, IV; Examples: protein complexes I, II, III, IV; Cytochrome Cytochrome c, c, ubiquinone (Q) ubiquinone (Q)
ETCETC
Proton Motive Force Proton Motive Force “Membrane Potential” “Membrane Potential”
During electron transportDuring electron transport protonsprotons are are also actively transported.also actively transported.
Protons accumulate in the Protons accumulate in the intermembrane space and create a intermembrane space and create a concentration gradient and charge concentration gradient and charge differencedifference——potential energy!potential energy!
This proton-motive force drives protons This proton-motive force drives protons back across the membrane.back across the membrane.
Proton Motive ForceProton Motive Force
I, III, and IV Pump Protons
ChemiosmosisChemiosmosis
Protons diffuse back into the Protons diffuse back into the mitochondria through ATP synthase, a mitochondria through ATP synthase, a channel protein.channel protein.
Diffusion is coupled to ATP synthesis.Diffusion is coupled to ATP synthesis.Oxidative PhosphorylationOxidative Phosphorylation is one is one
example of Chemiosmosisexample of Chemiosmosis
ATP SynthaseATP SynthaseFF00 subunit subunit: :
transmembranetransmembraneFF11 subunit subunit: projects : projects
into the into the mitochondrial mitochondrial matrix, rotates to matrix, rotates to expose active sites expose active sites for ATP synthesisfor ATP synthesis
Summary of Aerobic Summary of Aerobic RespirationRespiration
GlycolysisGlycolysis4 ATP – 2ATP used =2 ATP NET4 ATP – 2ATP used =2 ATP NET2 NADH2 NADH(IF FERMENTATION use 2 NADH to (IF FERMENTATION use 2 NADH to reduce pyruvate)reduce pyruvate)Pyruvate oxidationPyruvate oxidation2 NADH2 NADH2 CO2 2 CO2 TCA CycleTCA Cycle2 ATP2 ATP6 NADH6 NADH4 CO24 CO22 FADH22 FADH2
ETCETCNADH (TOTAL=10 x 2.5=25 ATP)NADH (TOTAL=10 x 2.5=25 ATP)FADH2 (2 x 1.5= 3 ATP)FADH2 (2 x 1.5= 3 ATP)Total ATP = 28Total ATP = 28
Total for Cell RespirationTotal for Cell Respiration4 ATP by substrate level 4 ATP by substrate level respirationrespiration28 ATP by oxidative 28 ATP by oxidative PhosphorylationPhosphorylation= 32 ATP= 32 ATP