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What’s thepoint? The pointis to makeATP! ATP
glucose pyruvate 6C 3C 2x Glycolysis • Breaking down glucose • “glyco – lysis” (splitting sugar) • ancient pathway which harvests energy • where energy transfer first evolved • transfer energy from organic molecules to ATP • still is starting point for all cellular respiration • but it’s inefficient • generate only2 ATP for every 1 glucose • occurs in cytosol In thecytosol?Why doesthat makeevolutionarysense?
Evolutionary perspective • Prokaryotes • first cells had no organelles • Anaerobic atmosphere • life on Earth first evolved withoutfree oxygen (O2) in atmosphere • energy had to be captured from organic molecules in absence of O2 • Prokaryotes that evolved glycolysis are ancestors of all modern life • ALL cells still utilize glycolysis You meanwe’re related?Do I have to invitethem over for the holidays?
enzyme enzyme enzyme enzyme enzyme enzyme enzyme enzyme ATP ATP 4 2 2 2 4 ADP NAD+ ADP 2Pi 2 2H 2Pi glucose C-C-C-C-C-C Overview 10 reactions • convert glucose (6C)to 2 pyruvate (3C) • produces:4 ATP & 2 NADH • consumes:2 ATP • net:2 ATP & 2 NADH fructose-1,6bP P-C-C-C-C-C-C-P DHAP P-C-C-C G3P C-C-C-P pyruvate C-C-C DHAP = dihydroxyacetone phosphate G3P = glyceraldehyde-3-phosphate
Glycolysis summary endergonic invest some ATP ENERGY INVESTMENT G3P C-C-C-P exergonic harvest a little ATP & a little NADH ENERGY PAYOFF 4ATP like $$in the bank yield 2 ATP 2 NADH NET YIELD
1st half of glycolysis (5 reactions) CH2OH Glucose “priming” O Glucose 1 ATP hexokinase • get glucose ready to split • phosphorylate glucose • molecular rearrangement • split destabilized glucose ADP CH2 O P O Glucose 6-phosphate 2 phosphoglucose isomerase CH2 P O CH2OH O Fructose 6-phosphate 3 ATP phosphofructokinase P O CH2 CH2 O P O ADP Fructose 1,6-bisphosphate aldolase 4,5 H O CH2 P isomerase C O C O Dihydroxyacetone phosphate Glyceraldehyde 3 -phosphate (G3P) CHOH CH2OH CH2 O P NAD+ Pi NAD+ Pi 6 glyceraldehyde 3-phosphate dehydrogenase NADH NADH P O O CHOH 1,3-Bisphosphoglycerate (BPG) 1,3-Bisphosphoglycerate (BPG) CH2 O P
2nd half of glycolysis (5 reactions) G3P C-C-C-P Energy Harvest • NADH production • G3P donates H • oxidize sugar • reduce NAD+ • NAD+ NADH • ATP production • G3P pyruvate • PEP sugar donates P • ADP ATP Pi Pi NAD+ NAD+ 6 NADH NADH 7 ADP ADP O- phosphoglycerate kinase C ATP ATP CHOH 3-Phosphoglycerate (3PG) 3-Phosphoglycerate (3PG) CH2 P O 8 O- phosphoglyceromutase O C H C O P 2-Phosphoglycerate (2PG) 2-Phosphoglycerate (2PG) CH2OH O- 9 H2O H2O enolase C O O C P Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) CH2 O- 10 ADP ADP C O pyruvate kinase Payola!Finally some ATP! ATP ATP C O CH3 Pyruvate Pyruvate
O- 9 H2O H2O enolase C O O C P Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) CH2 O- 10 ADP ADP C O pyruvate kinase ATP ATP C O CH3 Pyruvate Pyruvate Substrate-level Phosphorylation • In the last steps of glycolysis, where did the P come from to make ATP? • the sugar substrate (PEP) • P is transferred from PEP to ADP • kinase enzyme • ADP ATP ATP I get it! The PO4 camedirectly fromthe substrate!
2 ATP 2 ADP 4 ADP ATP 4 Energy accounting of glycolysis • Net gain = 2 ATP • some energy investment (-2 ATP) • small energy return (+4 ATP) • 1 6C sugar 2 3C sugars glucose pyruvate 6C 3C 2x All that work! And that’s all I get?
O2 O2 O2 O2 O2 3C 2x Is that all there is? • Not a lot of energy… • for 1 billon years+ this is how life on Earth survived • no O2= slow growth, slow reproduction • only harvest 3.5% of energy stored in glucose • more carbons to strip off = more energy to harvest glucose pyruvate 6C Hard wayto makea living!
DHAP G3P NAD+ Pi NAD+ Pi NADH NADH 1,3-BPG 1,3-BPG recycleNADH We can’t stop there! • Going to run out of NAD+ • without regenerating NAD+, energy production would stop! • another molecule must accept H from NADH Glycolysis glucose + 2ADP + 2Pi + 2 NAD+2pyruvate+2ATP+2NADH
recycleNADH How is NADH recycled to NAD+? with oxygen aerobic respiration without oxygen anaerobic respiration fermentation Another molecule must accept H from NADH pyruvate NAD+ H2O CO2 NADH NADH O2 acetaldehyde NADH acetyl-CoA NAD+ NAD+ lactate (lactic acid) which path you use depends on who you are… Krebs cycle ethanol
pyruvate ethanol + CO2 3C 2C 1C pyruvate lactic acid NADH NADH NAD+ NAD+ 3C 3C Fermentation (anaerobic) • Bacteria, yeast to glycolysis • beer, wine, bread • Animals, some fungi to glycolysis • cheese, anaerobic exercise (no O2)
pyruvate ethanol + CO2 3C 2C 1C NADH NAD+ bacteria yeast Alcohol Fermentation • Dead end process • at ~12% ethanol, kills yeast • can’t reverse the reaction Count thecarbons!
O2 pyruvate lactic acid NADH NAD+ 3C 3C animals Lactic Acid Fermentation • Reversible process • once O2 is available, lactate is converted back to pyruvate by the liver Count thecarbons!
O2 O2 Pyruvate is a branching point Pyruvate fermentation anaerobicrespiration mitochondria Kreb’s cycle aerobic respiration
What’s thepoint? The pointis to makeATP! ATP
H+ H+ H+ H+ H+ H+ H+ H+ + P H+ And how do we do that? • ATP synthase • set up a H+ gradient • allow H+ to flow through ATP synthase • powers bonding of Pi to ADP ADP + PiATP ADP ATP But… Have we done that yet?
NO!There’s still more to my story! Any Questions?