Fueling cellular processes

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Lecture 17

• Fueling cellular processes -
• glycolysis and oxidative phosphorylation

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Life obeys the laws of thermodynamics youve got
to eat!
First law of thermodynamics Second law of
thermodynamics
Energy is conserved
The entropy of an isolated system not in
equilibrium will tend to increase over time,
approaching a maximum value at equilibrium
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Some important equations
Gibbs free energy G H - TS Spontaneous ?G
?H - T?S lt 0 ? exergonic Not spontaneous ?G
?H - T?S gt 0 ? endergonic Equilibrium ?G 0
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Anabolism vs. catabolism
Anabolism Biosynthesis of biomolecules from
simpler components (usually endergonic) Catabolis
m Degradation of nutrients and cellular
components (usually exergonic)
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Anabolism vs. catabolism
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Trophic strategies
Autotrophs Photoautotrophs - photosynthesis Chem
olithotrophs - oxidation of inorganic compounds
such as NH3, H2S, Fe2 Heterotrophs Oxidation
of organic compounds
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Overview of catabolism
Complete oxidation of glucose C6H12O6 6 O2
? 6 CO2 6 H2O (?G -2850 kJ /
mol) Complete oxidation of palmitate C16H32O2
23 O2 ? 16 CO2 16 H2O (?G -9781 kJ / mol)
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A few additional equations
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Some standard free energies
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Coupled reactions
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ATP is a high-energy compound
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Glycolysis and oxidative phosphorylation
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Two stages of glycolysis
Stage 1
Stage 2
Glyceraldehyde- 3-phosphate dehydrogenase
Hexokinase
Phosphoglycerate kinase
Phosphoglucose isomerase
Phosphoglycerate mutase
Phosphofructo- kinase
Enolase
Aldolase
Pyruvate kinase
TIM
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Hexokinase - first step of glycolysis
Open
Closed
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GAPDH forms a high-energy intermediate
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GAPDH and PGK reactions are coupled
GAP Pi NAD ? 1,3-BPG NADH ?G 6.7
kJ/mol 1,3-BPG ADP ? 3PG ATP ?G -18.8
kJ/mol ___________________________________________
______ GAP Pi NAD ADP ? 1,3-BPG
NADH ATP ?G -12.1 kJ/mol
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PK - 2nd substrate-level phosphorylation
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Control of glycolysis
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Control of glycolysis - PFK
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Control of glycolysis - PFK
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Control of glycolysis - PFK
PFK
FBPase
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Overview of glucose metabolism
NADPH
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Metabolic fate of pyruvate
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Fermentation
Homolactic fermentation (muscle)
Alcoholic fermentation (yeast)
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Welcome to the mitochondrion
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Pyruvate dehydrogenase complex
E. coli 24x E2 dihydrolipoyl
transacetylase 24x E1 pyruvate
dehydrogenase 12x E3 dihydrolipoyl
dehydrogenase five coenzymes (thiamine
pyrophosphate, lipoic acid, CoA, FAD, NAD)
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Pyruvate dehydrogenase complex
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Pyruvate dehydrogenase complex
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Pyruvate dehydrogenase complex
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Pyruvate dehydrogenase complex
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Citric acid cycle
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Citric acid cycle
Step 1 Citrate synthase Condensation of
oxaloacetate and acetyl-CoA. ?G -31.5 kJ/mol
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Citrate synthase mechanism
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Citric acid cycle
Step 2 Aconitase Reversible isomerization,
dehydration/hydration mechanism
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Citric acid cycle
Step 3 Isocitrate dehydrogenase Oxidative
decarboxylation, generation of NADH
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Citric acid cycle
Step 4 a-Ketoglutarate dehydrogenase Oxidative
decarboxylation, similar to PDH (share E3)
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Citric acid cycle
Step 5 Succinyl-CoA synthetase Substrate-level
phosphorylation
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Citric acid cycle
Step 6 Succinate dehydrogenase Oxidation of
alkane to alkene, membrane bound!
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Citric acid cycle
Step 7 Fumarase Hydration reaction
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Citric acid cycle
Step 8 Malate dehydrogenase Regeneration of
malate, endergonic
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Regulation of the citric acid cycle
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Regulation of the citric acid cycle
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The citric acid cycle is amphibolic
Green Anaplerotic reactions (replenish) Red Cat
aplerotic reactions (drain)
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A little bookkeeping
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Oxidation of glucose
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Conservation of ?G from NADH oxidation in a pH
gradient
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Conservation of ?G from NADH oxidation in a pH
gradient
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Conservation of ?G from NADH oxidation in a pH
gradient
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Complex I NADHubiquinone oxidoreductase
Sazanov Hinchliffe (2006)
Grigorieff (1998)
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Complex I NADHubiquinone oxidoreductase
Sazanov Hinchliffe (2006)
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Bacteriorhodopsin as a model proton pump
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Coenzyme Q and complex III CoQcytochrome c
oxidoreductase
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Coenzyme Q and complex III CoQcytochrome c
oxidoreductase
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The Q cycle proton pumping through direct
coupling
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Complex IV cytochrome c oxidase
410 kDa homodimer, 13 subunits per protomer, 4
redox centers
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Complex IV cytochrome c oxidase
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The mitochondrial electron transport chain
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Complex V ATP synthase
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Function of the mitochondrial ATP synthase
mitochondrial matrix
intermembrane space
Junge, Bereiter-Hahn IWF (1999)
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(No Transcript)
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ATP synthase as drug target
First new antituberculosis drug in 40 years. Now
in Phase IIb clinical trials.
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OXPHOS supercomplexes
I III2 III2 IV2 V2
Boekema Braun (2007)
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A little more bookkeeping
3 ATP for each NADH 2 ATP for each FADH2
ATP
NADH
FADH2
GTP
Process
Glycolysis
2
2
PDH
2
TCA
2
2
6
ATP Yield
2
2
4
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A little more bookkeeping
3 ATP for each NADH 2 ATP for each FADH2
But transport of molecules across membranes to
the mitochondria reduces the final yield
ATP
NADH
FADH2
GTP
Process
Glycolysis
2
2
PDH
2
TCA
2
2
6

ATP Yield
2
2
3
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