Cellular Respiration. To get a better understanding of how cellular respiration takes place in our bodies at a cellular level please take the time to.

Chapter 4

Chapter 4Cellular Respiration

Watch the following videos!!To get a better understanding of how cellular respiration takes place in our bodies at a cellular level please take the time to watch the following videos!http://www.youtube.com/watch?v=00jbG_cfGuQ

http://www.khanacademy.org/science/biology/cellular-respiration/v/introduction-to-cellular-respirationAerobic Cellular RespirationProcess that extracts energy from food (mainly glucose, but also proteins and lipids) in the presence of oxygen obligate aerobes

The energy that is extracted is used to synthesize ATP

ATP is used to supply energy directly to cells to drive chemical reactions

Aerobic Cellular RespirationDivided into 4 stagesGlycolysisPyruvate oxidationCitric acid cycleElectron transport and oxidative phosphorylationEach Stage involves the transfer of FREE ENERGYATP is produced in two different waysSubstrate-level phosphorylationOxidative phosphorylation

Aerobic RespirationLocation of each StageGlycolysisCytosolPyruvate OxidationMitochondrionCitric Acid CycleMitochondrionElectron Transport Mitochondrion

GlycolysisPrimitiveProcess found in almost all organismsBoth prokaryotes and eukaryotes Does not require OInvolves Soluble enzymes 10 sequential enzyme-catalyzed reactions Oxidation of a 6-carbon sugar glucoseProduces2 molecules of pyruvate (3-carbon molecule)2 ATP and 2 NADHTwo Phases in which this occurs Initial energy investment phase Energy payoff phase

This process is for the conversion of only ONE glucose molecule!!!http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_glycolysis_works.htmlGlycolysis (Initial Energy Investment Phase)Step 1Glucose receives a phosphate group from ATPProduces glucose-6-phosphateEnzyme usedhexokinase

Glycolysis (Initial Energy Investment Phase)Step 2Glucose-6-phosphate is rearranged into its isomerProduces fuctose-6-phosphateEnzyme usedPhospho-glucomutaseRecall IsomersSame molecular formula but different structure

Glycolysis (Initial Energy Investment Phase)Step 3Fructose-6-phosphate receives another phosphate group from ATPProduces fructose-1,6-bisphosphateEnzyme UsedPhospho-fructokinase

Glycolysis (Initial Energy Investment Phase)Step 4 Fructose-1,6-bisphosphate is splitProduces Glyceraldehyde-3-phosphate (G3P)Dihydroxyacetone phosphate (DHAP)Enzyme usedaldolase

Glycolysis (Initial Energy Investment Phase)Step 5Dihydroxyacetone (DHAP) is converted Produces glyceraldehyde-3-phosphate (G3P)Enzyme usedTriosephosphate-isomeraseThis is the last step of the initial energy investment phaseTotal of 2 ATP investedEnd result is 2 G3P molecules

IMPORTANT!!!Because there are now 2 molecules of G3P at the end of the initial energy investment phase, all the reactions in the energy payoff phase (6 to 10) are DOUBLED!!Glycolysis (Energy Payoff Phase)Step 62 electrons and 2 protons are removed from G3PNAD accepts both electrons and a proton (becoming NADH)Other proton is released into cytosolPhosphate group is attachedProduces Two 1,3-bisphosphoglycerateEnzyme used Triosephosphate-dehydrogenase

Glycolysis (Energy Payoff Phase)Step 7A phosphate group from 1,3-bisphosphoglycerate is transferred to ADPProduces2 ATPTwo 3-phosphoglycerate Enzyme usedPhosphoglycerate kinaseATP is produced by Substrate-level phosphorylation

Glycolysis (Energy Payoff Phase)Step 83-phosphoglycerate is rearranged Phosphate group is shifted from 3-carbon to 2-carbonProducesTwo 2-phosphoglycerateThis process is done via mutase reactionShifting of a chemical group to another within the same moleculeEnzyme usedphosphoglucomutase

Glycolysis (Energy Payoff Phase)Step 9Electrons are removed from one part of 2-phosphoglycerate and delivered to another part of the moleculeProduces Two HO molecules Two PhosphoenolpyruvateEnzyme used Enolase

Glycolysis (Energy Payoff Phase)Step 10Final phosphate group is transferred from phosphoenolpyruvate (PEP) to ADPProduces2 ATP Two Pyruvate molecules Enzyme used Pyruvate kinaseATP is produced by Substrate-level phosphorylation

Substrate-Level Phosphorylation Phosphate groups are attached to ADP from a substrate forming ATP (enzyme catalyzed reaction)ALL ATP molecules are produced this way in Glycolysis

Overview of GlycolysisInitial energy investment phase2 ATP are consumed

Energy payoff phase4 ATP produced2 NADH molecules are synthesized

Overall NET reaction; Glucose + 2 ADP + 2 Pi + 2 NAD 2 pyruvate + 2 ATP + 2 NADH + 2H

62 kJ of energy is stored by the synthesis of 2 ATP molecules Rest of the free energy is stored in the 2 pyruvate moleculeshttp://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_the_nad__works.htmlPyruvate Oxididation Remember glycolysis occurs in the cytosol of the cell

The Citric Acid Cycle (next step) occurs in the mitochondrial matrix

Pyruvate must pass through the inner and outer membrane of the mitochondrion

Pyruvate OxidationMulti-step processOuter membranePyruvate diffuses across the outer membrane through large pores of mitochondrion

Inner membranePyruvate-specific membrane carrier is required

Inside MatrixPyruvate is converted into an acetyl groupAcetyl group is bonded to coenzyme AProduces an acetyl-CoA complex

Pyruvate OxidationConversion of pyruvate to acetyl-CoAInvolves 2 Reactions1. Decarboxylation reactionCarboxyl group (-COO) of pyruvate is removed ProducesCO2. Dehydrogenation reaction2 electrons and a proton are transferred Produces NADH H in solutionNet reaction2 pyruvate + 2 NAD + 2 CoA 2 acetyl-CoA + 2 NADH + 2 H + 2 CO

Pyruvate OxidationAcetyl group reacts with the sulfur atom of coenzyme AAcetyl-CoA is the molecule that will start the Citric Acid Cycle

Citric Acid CycleDiscovered bySir Hans Krebs (1900-1981)

Consists of 8 enzyme catalyzed reaction

ALL ATP are produced by substrate-level phosphorylationhttp://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cycle_works__quiz_1_.html

Citric Acid CycleStep 12-carbon acetyl group carried by coenzyme A is transferred to oxaloacetateProduces CitrateEnzyme used Citrate synthase

Citric Acid CycleStep 2Citrate is rearranged into its isomerProduces IsocitrateEnzyme usedAconitase

Citric Acid CycleStep 3Isocitrate is oxidized Produces -ketoglutarateNADHCOHEnzyme used Isocitrate dehydrogenase

Citric Acid CycleStep 4-ketoglutarate is oxidizedProducesSuccinyl CoACONADHEnzyme used-ketoglutarate dehydrogenase

Citric Acid CycleStep 5 CoA is released from succinyl CoAProducesSuccinateEnergy released converts GDP to GTP which couples production of ATPEnzyme usedSuccinyl CoA synthetaseGTPActivates substrate to produce ATP

Citric Acid CycleStep 6Succinate is oxidizedProducesFumarateFADHEnzyme used Succinate dehydrogenaseFADHNucleotide-based moleculeElectron carrier

Citric Acid CycleStep 7Fumarate is converted with the addition of HOProducesMalateEnzyme usedFumarase

Citric Acid CycleStep 8Malate is oxidized Produces OxaloacetateNADHHEnzyme usedMalate dehydrogenase

Overview of Citric Acid Cycle2 molecules of pyruvate are converted to Acetyl-CoACitric Acid Cycle goes through two turns for every single glucose molecule that is oxidized

1 Turn: Acetyl-CoA + 3 NAD + FAD + ADP + Pi 2 CO + 3 NADH + 3 H + FADH + ATP + CoA

ATP is synthesized by substrate level phosphorylation coupled by GTP

Citric Acid CycleALL of the carbon atoms that make up a glucose molecule are converted into COoxidation of pyruvate acetyl groups

6COOxidation of ONE Glucose MoleculeTotal # of NET Molecules Produced NADHFADHCOATPGlycolysis2002Pyruvate Oxidation2020Citric Acid Cycle6242Electron Transport Chain ChemiosmosisProcess that extracts potential energy that is stored in NADH and FADHThese molecules were formed during glycolysis, pyruvate oxidation, and citric acid cycleThis energy is used to synthesize additional ATP (A lot more) The Electron Transport ChainOccurs on the inner mitochondrial membraneFacilitates the transfer of electrons from NADH and FADH to O

The Electron Transport ChainComposed of 4 ComplexesComplex I, NADH dehydrogenase Complex II, succinate dehydrogenaseComplex III, cytochrome complexComplex IV, cytochrome oxidase2 Electron shuttlesUbiquinone (UQ)Hydrophobic molecule shuttles electrons from complex I and II to complex IIICytochrome C (cyt c)Shuttles electrons from complex III to complex IV

The Driving Force Behind Electron Transport Complexes I, III, IVEach has a cofactorEach cofactor has increasing electronegativityAlternate between reduced and oxidized statesElectrons move towards more electronegative molecules (downstream)Final electron acceptor OXYGEN (most electronegative)Pulls electrons from complex IVhttp://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__electron_transport_system_and_atp_synthesis__quiz_1_.htmlHow a Single Oxygen Atom Works (O) Final electron acceptor Removes two electrons from complex IVReacts with 2 H to produce HOBUT WE BREATH IN O NOT A SINGLE OSo for every O molecule Pulls a total of 4 electrons through the electron transport chain2 HO molecules are produced Pulling 4 electrons from complex IV triggers a chain reaction between other complexes!!

What happens in this chain of reactions?Starts with OPulls electrons through the chain of complexesNADH is least electronegative but contains most free energyO has highest electronegativity but contains least amount of free energy

Proton GradientElectron Transport from NADH or FADH to O does not produce any ATP!!What does?Proton GradientTransport of H ions across the inner mitochondrial membrane from the matrix into the inter-membrane spaceCreatesProton-Motive ForceChemical gradient (difference in concentrations)Electro potential gradient is created (because of the positive charge on Hydrogen atom)

Proton Gradient

ChemiosmosisThe ability of cells to use the proton-motive force to do workSynthesizes ATP using electrochemical gradientUses ATP synthase enzymeATP is synthesized using oxidative phosphorylation Oxidative PhosphorylationRelies on ATP synthaseForms a channel which H ions can pass freely H ions cause the synthase to rotate harnessing potential energy to synthesize ATP

Efficiency of Cellular Respiration

NADH and FADHNADH produced during glycolysis is in cytosol Transported into mitochondria via two shuttle systemsMalate-aspartate shuttleGlycerol-phosphate shuttle

Glycolysis 2 ATPCitric Acid Cycle2 ATPElectron Transport34 ATPTotal 38 ATPNADH and FADHFor every NADH that is oxidizedAbout 3 ATP are synthesized10 NADH x 3 ATP = 30 ATP For every FADHAbout 2 ATP are synthesized2 FADH x 2 ATP = 4 ATP

Total of 34 ATP synthesized by electron transport chainEfficiency of Cellular Respiration38 ATP produced Hydrolysis of ATP yields 31kJ/mol31 kJ/mol x 38 ATP = 1178 kJ/mol

Glucose contains 2870 kJ/mol of energy

Only 41% of the energy in glucose in converted into ATPThe rest is lost as thermal energy

Cells that need a constant supply of ATPBrain cells, muscle cellsNeed burst of ATP during periods of activity

Creatine phosphate pathwayCreatine is phosphorylated High energy moleculeStored within cell Used to generate additional ATP when needed

creatine + ATP creatine phosphate + ADPcreatine phosphate creatine + ATP

Cells that dont need to produce ATPUncoupling Proteins in mitochondria provide a different path for HInstead of producing ATP, thermal energy is releasedBrown adipose tissueImportant for the maintenance of body temperature Hibernating mammals

Metabolic RatesAmount of energy an organism expends over a specified timeIncrease energy use when work incresesBasal metabolic rate (BMR)kJ/m/hAmount of energy used during a state of restHigher % of body fat reduces metabolic rateCellular Respiration Regulated Feedback inhibitionEnzyme used PhosphofructokinaseInhibited byHigh levels of ATPHigh levels of citrateActivated byLow levels of ADPLow levels of AMP GlucoseStored as glycogen

Alternatives to GlucoseDisaccharide carbohydratesHydrolyzed into glucose, fructose, galactoseGlycogen is hydrolyzed by enzymes in liverProduce glucose-6-phosphateFatsTriglycerides Hydrolyzed into glycerol Converted into glyceraldehyde-3-phosphate Fatty AcidsSplit into 2 carbon fragments Become acetyl groups attach to CoAProteinsHydrolyzed into amino acids -NH is removed and the rest enters as pyruvate, acetyl groups

Anaerobic Pathways: Without OxygenTwo pathwaysFermentation (not a form of respiration)Uses an organic molecule as a final electron acceptor Does not use an electron transport chain Anaerobic respirationUses an inorganic substance as the final electron acceptorUses an electron transport chainFermentationAbsence of oxygenReactions used to oxidize NADHAllows glycolysis to continueTwo formsEthanol fermentationLactic acid fermentation

Alcohol FermentationOccurs in Bacteria, yeastsProcess Pyruvate is decarboxylated Produces acetaldehydeAcetaldehyde oxidizes NADHProductsCO EthanolNAD

Facultative anaerobes -survive with or without oxygenAlcohol FermentationFinal reaction:

pyruvate + NADH + H NAD + CO + ethanol

Glycolysis included (2 pyruvate molecules)

glucose + 2 ADP + 2 Pi 2 ATP + 2CO + 2 ethanol

Fermentation produces only 2 ATP!!!Lactate FermentationOccurs in humans whenDemand for ATP exceeds the rate at which O can be supplied Process Pyruvate is converted into lactateLactate regenerates NADGlycolysis continues

Lactate FermentationFinal reaction

pyruvate + NADH + H NAD + lactate Glycolysis included

glucose + 2 ADP + 2Pi lactate + 2ATP

Fermentation only produces 2 ATP!!!Anaerobic Respiration Obligate anaerobesCannot survive in the presence of oxygenLack mitochondria Have electron transport chains Inorganic terminal electron acceptor Sulfate SONitrate NOIron ion FeMany prokaryotes, protists