Overview of cellular respiration4 metabolic stagesAnaerobic respiration1. Glycolysisrespiration without O2in cytosolAerobic respirationrespiration using O2in mitochondria2. Pyruvate oxidation3. Krebs cycle4. Electron transport chain(+ heat)
What is Cellular Respiration?Step-by-step breakdown of high-energy glucose molecules to release energy Takes place day and night in all living cellsOccurs in stages, controlled by enzymes
1. Glycolysis (splitting of sugar) a. cytosol, just outside of mitochondria.Grooming Phase a. migration from cytosol to matrix.Krebs Cycle (Citric Acid Cycle) a. mitochondrial matrix4. Electron Transport Chain (ETC) and Oxidative Phosphorylationa. Also called Chemiosmosisb. inner mitochondrial membrane.
Breakdown of Cellular Respiration
ATP Energy Currency of CellsAn ATP molecule contains potential energy, much like a compressed spring. When a phosphate group is pulled away during a chemical reaction, energy is released.
This cycle is the fundamental mode of energy exchange in biological systems.ATP-ADP Cycle
ATP-ADP CycleATP is constantly recycled in your cells. A working muscle cell recycles all of its ATP molecules about once each minute. That's 10 million ATP molecules spent and regenerated per second!
Different types of Cellular RespirationAerobic respiration Occurs in the presence of oxygenWhen chemically breaking down glucose completely, this process releases large amounts energy- Releasing carbon dioxide and water as waste products.
Anaerobic respiration-Occurs if there is a lack of oxygen available for aerobic respiration-Only Glycolysis occurs-Glucose is incompletely broken down -In this type of respiration a lot less energy is -produced and most of it is lost as heat.
Glycolysis Breaking down glucose glyco lysis (splitting sugar)
ancient pathway which harvests energywhere energy transfer first evolvedtransfer energy from organic molecules to ATPstill is starting point for all cellular respirationbut its inefficient generate only 2 ATP for every 1 glucoseoccurs in cytosolIn the cytosol? Why does that make evolutionary sense?
Evolutionary perspectiveProkaryotesfirst cells had no organellesAnaerobic atmospherelife on Earth first evolved without free oxygen (O2) in atmosphereenergy had to be captured from organic molecules in absence of O2Prokaryotes that evolved glycolysis are ancestors of all modern lifeALL cells still utilize glycolysisYou mean were related? Do I have to invite them over for the holidays?
10 reactionsconvert glucose (6C) to 2 pyruvate (3C) produces: 4 ATP & 2 NADHconsumes: 2 ATPnet: 2 ATP & 2 NADHglucoseC-C-C-C-C-Cfructose-1,6bPP-C-C-C-C-C-C-PDHAPP-C-C-C G3PC-C-C-PpyruvateC-C-COverviewDHAP = dihydroxyacetone phosphateG3P = glyceraldehyde-3-phosphate
Pi364,5ADPNAD+GlucosehexokinasephosphoglucoseisomerasephosphofructokinaseGlyceraldehyde 3-phosphate (G3P)DihydroxyacetonephosphateGlucose 6-phosphateFructose 6-phosphateFructose 1,6-bisphosphateisomeraseglyceraldehyde3-phosphatedehydrogenasealdolase1,3-Bisphosphoglycerate(BPG)1,3-Bisphosphoglycerate(BPG)12ATPADPATPNADHNAD+NADHPiCH2COCH2OHPOCH2OPOCHOHCCH2OPOCHOHCH2OPOCH2OP OPOCH2HCH2OHOCH2POOCH2OHPO1st half of glycolysis (5 reactions)Glucose primingget glucose ready to splitphosphorylate glucose molecular rearrangementsplit destabilized glucose
2nd half of glycolysis (5 reactions)Payola! Finally some ATP!
NADH productionG3P donates Hoxidize sugarreduce NAD+NAD+ NADHATP productionG3P pyruvatePEP sugar donates PADP ATP78H2O910ADPATP3-Phosphoglycerate(3PG)3-Phosphoglycerate(3PG)2-Phosphoglycerate(2PG)2-Phosphoglycerate(2PG)Phosphoenolpyruvate(PEP)Phosphoenolpyruvate(PEP)PyruvatePyruvatephosphoglyceratekinasephosphoglyceromutaseenolasepyruvate kinaseADPATPADPATPADPATPH2OCH2OHCH3CH2O-OCPHCHOHO-O-O-CCCCCCPPOOOOOOCH2NAD+NADHNAD+NADHEnergy Harvest G3PC-C-C-PPiPi6
Substrate-level PhosphorylationP is transferred from PEP to ADPkinase enzymeADP ATPI get it!The PO4 came directly from the substrate!In the last steps of glycolysis, where did the P come from to make ATP?the sugar substrate (PEP)ATP
Substrate-Level PhosphorylationATP is formed when an enzyme transfers a phosphate group from a substrate to ADP.Example:PEP to PYR
Energy accounting of glycolysis Net gain = 2 ATPsome energy investment (-2 ATP)small energy return (+4 ATP)1 6C sugar 2 3C sugarsglucose pyruvate2x6C3CAll that work! And thats all I get?
Is that all there is?Not a lot of energyfor 1 billon years+ this is how life on Earth survivedno O2= slow growth, slow reproductiononly harvest 3.5% of energy stored in glucosemore carbons to strip off = more energy to harvestHard way to make a living! glucose pyruvate6C
GlycolysisSplits a glucosemolecule into 2 - 3 Carbon molecules calledPYRUVATE.products: 2 ATP, NADH and pyruvate
glucose + 2ADP + 2Pi + 2 NAD+ 2 pyruvate + 2ATP + 2NADHWe cant stop there!Going to run out of NAD+without regenerating NAD+, energy production would stop!another molecule must accept H from NADH
NADHpyruvateacetyl-CoAlactateethanolNAD+NAD+NADHNAD+NADHCO2acetaldehydeH2OKrebscycleO2(lactic acid)with oxygenaerobic respirationwithout oxygenanaerobic respirationfermentationHow is NADH recycled to NAD+?Another molecule must accept H from NADHwhich path you use depends on who you are
Fermentation (anaerobic)Bacteria, yeastAnimals, some fungibeer, wine, breadcheese, anaerobic exercise (no O2)to glycolysisto glycolysis
Alcohol FermentationCount the carbons! Dead end processat ~12% ethanol, kills yeastcant reverse the reactionbacteria yeast
Reversible processonce O2 is available, lactate is converted back to pyruvate by the liverLactic Acid FermentationCount the carbons! animals
Pyruvate is a branching pointPyruvatemitochondriaKrebs cycleaerobic respirationfermentationanaerobic respiration
Without OxygenNo O2Alcoholic FermentationLactic Acid Fermentation
Whats the point?The point is to make ATP!ATP
And how do we do that?ATPBut Have we done that yet?ADPATP synthaseset up a H+ gradientallow H+ to flow through ATP synthasepowers bonding of Pi to ADP
ADP + Pi ATP
NO! Theres still more to my story!Any Questions?
Metabolism in the mitochondrial matrixOooooh! Form fits function!
Oxidation of pyruvate3C2C1CPyruvate enters mitochondria
3 step oxidation processreleases 1 CO2 (count the carbons!)reduces 2 NAD 2 NADH (moves e-)produces acetyl CoAAcetyl CoA enters Krebs cycleWhere does the CO2 go?Exhale!
Pyruvate oxidized to Acetyl CoA Yield = 2C sugar + NADH + CO2reductionoxidationCoenzyme APyruvateAcetyl CoAC-C-CC-CCO2
Krebs cycleaka Citric Acid Cyclein mitochondrial matrix8 step pathwayeach catalyzed by specific enzymestep-wise catabolism of 6C citrate moleculeEvolved later than glycolysisdoes that make evolutionary sense?bacteria 3.5 billion years ago (glycolysis)free O2 2.7 billion years ago (photosynthesis)eukaryotes 1.5 billion years ago (aerobic respiration = organelles mitochondria)1937 | 1953Hans Krebs1900-1981
citrateacetyl CoACount the carbons!pyruvatex 2oxidation of sugarsThis happens twice for each glucose molecule
citrateacetyl CoACount the electron carriers!pyruvatereduction of electron carriersThis happens twice for each glucose moleculex2
So we fully oxidized glucose C6H12O6CO2& ended up with 4 ATP!Whassup?Whats the point?
Krebs cycle produces large quantities of electron carriersNADHFADH2go to Electron Transport ChainElectron Carriers = Hydrogen CarriersWhats so important about electron carriers? ATPADP + Pi
Energy accounting of Krebs cycle Net gain=2 ATP =8 NADH + 2 FADH2ATPpyruvate CO23C
Value of Krebs cycle?If the yield is only 2 ATP then how was the Krebs cycle an adaptation?value of NADH & FADH2electron carriers & H carriersreduced molecules move electronsreduced molecules move H+ ionsto be used in the Electron Transport Chainlike $$ in the bank
ATP accounting so farGlycolysis 2 ATP Krebs cycle 2 ATP Life takes a lot of energy to run, need to extract more energy than 4 ATP!Whats the point? A working muscle recycles over 10 million ATPs per secondTheres got to be a better way!
There is a better way!Electron Transport Chain series of molecules built into inner mitochondrial membranealong cristaetransport proteins & enzymes transport of electrons down ETC linked to pumping of H+ to create H+ gradientyields ~34 ATP from 1 glucose!only in presence of O2 (aerobic respiration)That sounds more like it!
Electron Transport ChainIntermembrane spaceMitochondrial matrixQCNADH dehydrogenasecytochrome bc complexcytochrome c oxidase complex
G3PGlycolysisKrebs cycle8 NADH2 FADH2Remember the Electron Carriers? 4 NADHTime to break open the bank!glucose
Electron Transport Chainintermembrane spacemitochondrial matrixinner mitochondrial membraneNAD+QCNADH H2OH+e 2H+ + O2 H+H+eFADH2NADH dehydrogenasecytochrome bc complexcytochrome c oxidase complexFADeHH e- + H+NADH NAD+ + HHBuilding proton gradient!What powers the proton (H+) pumps?
ATPStripping H from Electron CarriersNADH passes electrons to ETCH cleaved off NADH & FADH2electrons stripped from H atoms H+ (protons)electrons passed from one electron carrier to next in mitochondrial membrane (ETC)transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane spaceADP + PiTA-DA!!Moving electrons