2 ATP+ 4 ATP= + 2 ATP
So does this solve the direction problem? Only for a second Where does this ATP come from, if we are E. coli growing in minimal mediumGlucose is the only carbon source.Need to make ATP from glucose, and this TAKES energy.Need only to regenerate ATP from ADP:Via GLYCOLYSIS, e.g.
Overall reaction of glycolysis to pyruvate INCLUDING the generation of ATP
1 glucose + 2 ADP + 2 Pi + 2 NAD 2 pyruvate + 2 ATP + 2 NADH2 Go = -18 kcal/mole
So overall reaction goes essentially completely to the right.
The second way the cell gets a reaction to go in the desired direction:1) A coupled reaction.One of two ways the cell solves the problem of getting a reaction to go in the desired direction Glucose + ATP glucose-6-P04 + ADP, Go = -3.4 kcal/mole2) The second way:Removal of the product of an energetically unfavorable reactionUses a favorable downstream reactionPulls the unfavorable reactionOperates on the second term of the G equation. G = Go + RTln([products]/[reactants])
So glucose pyruvic acid
ADP ATP, as long as we have plenty of glucoseAre we all set?
No. What about the NAD.. We left it burdened with those electrons. Soon all of the NAD will be in the form of NADH2
Glycolysis will screech to a halt !!Need an oxidizing agent in plentiful supply to keep taking those electron off the NADH2, to regenerate NAD so we can continue to run glucose through the glycolytic pathway.
Oxidizing agents around for NAD:1) Oxygen Defer2) PyruvateIn E. coli, humans:Pyruvate lactate, NADH2 NAD, coupled
In Yeast: Pyruvate ethanol + CO2
Fermentation: anaerobiosis (no oxygen)Lactate fermentation
Mutually exclusive, depends on organism
Other types, less common fermentations, exist(e.g., propionic acid fermentation, going on in Swiss cheese)
The efficiency of fermentationglucose--> 2 lactates, without considering the couplings for the formation of ATP's (no energy harnessing): Go = -45 kcal/mole So 45 kcal/mole to work with.Out of this comes 2 ATPs, worth 14 kcal/mol. So the efficiency is about 14/45 = ~30%Where did the other 31/45 kcal/mole go?Wasted as HEAT.
Fermentation goes all the way to the rightSince 2 ATPs ARE produced, taking them into account, for the reaction:Glucose + 2 ADP + 2 Pi 2 lactate + 2 ATPGo = -31 kcal/mole (45-14)Very favorable.All the way to the right. Keep bringing in glucose, keep spewing out lactate,Make all the ATP you want.
glucose--> 2 lactates, without considering the couplings for the formation of ATP's (no energy harnessing): Go = -45 kcal/mole kcal/mole Out of this comes 2 ATPs, worth 14 kcal/mol. So the efficiency is about 14/45 = ~30%Thats fermentation, for now.
Energy yieldComplete oxidation of glucose,Much more ATPBut natures solution is a bit complicated.The fate of pyruvate is now different
But all this spewing turns out to be wasteful.Glucose could be completely oxidized, to: CO2That is, burned.How much energy released then?Glucose + 6 O2 6 CO2 + 6 H2O Go = -686 kcal/mole !Compared to -45 to lactate (both w/o/ ATP considered)
2 NADH2 NADH
Acetyl-CoA O ||CH3 - C OH + Co-enzyme A Acetyl ~CoA Acetic acid, acetate
Acetyl-CoA2 CO22 CO22 CO22 oxaloacetatePer glucose2 NADH 2 NADH2 NADH2 NADH
GTP is energetically equivalent to ATPGTP + ADP GDP + ATP
Go = ~0
G= guanine (instead of adenine in ATP)
2 NADH2 NADH2 NADH2 NADH
2 ATP2 ATP
Acetyl-CoA2 CO22 CO22 CO2
2 Succinic dehydrogenase2 oxaloacetatePer glucose
FAD = flavin adenine dinucleotideFAD + 2H. FADH2
2 NADH2 NADH2 NADH2 NADH2 FADH22 NADH
2 ATP2 ATP
Acetyl-CoA2 CO22 CO22 CO2
Succinic dehydrogenaseoxaloacetatePer glucose
2 NADH2 NADH2 NADH2 NADH2 FADH22 NADH2 ATP2 ATP
2 CO22 CO22 CO2
Glucose + 6 O2 6 CO2 + 6 H2O :
By glycolysis plus one turn of the Krebs Cycle:1 glucose (6C) 2 pyruvate (3C) 6 CO22 X 5 NADH2 and 2 X 1 FADH2 produced per glucose4 ATPs per glucoseNADH2 and FADH2 still must be reoxidized .No oxygen yet to be consumedNo water produced yetPer glucose
Oxidation of NAD by O2NADH2 + 1/2 O2 --> NAD + H2OGo = -53 kcal/mole
If coupled directly to ADP ATP (7 kcal cost), 46 kcal/mole waste, and heat
So the electrons on NADH (and FADH2) are not passed directly to oxygen, but to intermediate carriers,
Each transfer step involves a smaller packet of free negative energy change (release)
Handout 8-3 NADH2Ubiquinone; Coenzyme QHH
nalSchematic idea of H+ being pumped outHandout 8-4
FoF1 complexHandout 8-4
Proton motive force (pmf)Chemical gradientElectrical gradient Electrochemical gradient
Peter Mitchell 1961
H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+H+ETC Complex IsNADHH+H+H+H+H+H+H+H+H+H+H+H+NADHArtificial phospholipid membranepH dropspH rises
Artificially produced mitochondrial membrane vesicleATP is formed from ADP + Pi
Dinitrophenol (DNP): an uncoupler of oxidative phosphorylationDNPs -OH is weakly acidic in this environment
DNP can easily permeate the mitochondrial inner membrane
Outside the mitochondrion, where the H+ concentration is high, DNP picks up a proton
After diffusing inside, where the H+ concentration low, it gives up the proton.
So it ferries protons from regions of high concentration to regions of low concentration, thus destroying the proton gradient.
Electron transport chain goes merrily on and on, but no gradient is formed and no ATP is produced.
The mechanism of ATP formation:
The ATP synthetase (or ATP synthase)
The F0F1 complex
Testing the ATP synthetase motor model by running it in reverse (no H+ gradient, add ATP)Actin labeledBy tagging it with fluorescent molecules Actin is a muscle protein polymer
12345Run reaction in reverse, add ATP, drive counter-clockwise rotation of camATP hydrolysisThis is oxidative phosphorylation of ADP
Testing the ATP synthetase motor model by running it in reverseActin labeledBy tagging it with fluorescent molecules Actin is a muscle protein polymer
ATP accountingEach of the 3 ETC complex (I, III, IV) pumps enough H+ ions to allow the formation of 1 ATP.So 3 ATPs per pair of electrons passing through the full ETC.So 3 ATPs per 1/2 O2 So 3 ATPs per NADH2But only 2 ATPs per FADH2 (skips complex 1)
Similar to handout 8-2
Grand total (E. coli):17 + 2 = 19 per glucoseor 38 per 1 glucoseHandout 8-6
ATP accounting38 ATP/ glucose in E. coli
36 ATP/glucose in eukaryotesCost of bringing in the electrons from NADH from glycolysis into the mitochondrion = 1 ATP per electron pair So costs 2 ATPs per glucose, subtract from 38 to get 36 net.
Efficiency36 ATP/ glucose, worth 7 X 36 = 252 kcal/mole of glucose
Go for the overall reaction glucose + 6 O2 6CO2 + 6 H2O:-686 kcal/ moleEfficiency = 252/686 = 37%
Once again, better than most gasoline engines.
and Energy yield:36 ATP/ glucose vs. 2 ATP/glucose in fermentation(yet fermentation works)
So with or without oxygen, get energy from glucose
Cellular location (eukaryotes):CYTOPLASMMITOCHONDRIAHandout 8-6
Nucleic acidsProf. Mowshowitz, next timeBut wait:
I will be back for one more lecture (#11) on energy metabolism and intermediary metabolism