Cellular Respiration Stage 1: (Glycolysis)
What s the point? The point is to make!
Glycolysis: Breaking down glucose glyco lysis (splitting sugar) glucose pyruvate 6C 2x 3C In the cytosol? Why does that make evolutionary sense? ancient pathway which harvests energy where energy transfer first evolved transfer energy from organic molecules to still is starting point for ALL cellular respiration but it s inefficient generate only 2 for every 1 glucose occurs in cytosol That s not enough for me!
Evolutionary perspective: Prokaryotes first cells had no organelles Anaerobic atmosphere life on Earth first evolved without free oxygen (O 2 ) in atmosphere energy had to be captured from organic molecules in absence of O 2 Prokaryotes that evolved glycolysis are ancestors of all modern life ALL cells still utilize glycolysis Enzymes of glycolysis are well-conserved You mean we re related? Do I have to invite them over for the holidays?
Overview: 10 reactions convert glucose (6C) to 2 pyruvate (3C) produces: 4 & 2 consumes: 2 net yield: 2 & 2 glucose C-C-C-C-C-C fructose-1,6bp P-C-C-C-C-C-C-P enzyme DHAP P-C-C-C DHAP = dihydroxyacetone phosphate G3P = glyceraldehyde-3-phosphate enzyme enzyme enzyme 2P i enzyme 2 2 G3P C-C-C-P enzyme enzyme enzyme 2H 2P i pyruvate C-C-C 2 2 4 4 NAD +
Glycolysis summary: endergonic ENERGY INVESTMENT invest some ENERGY PAYOFF G3P C-C-C-P -2 4 exergonic harvest a little & a little like $$ in the bank NET YIELD net yield 2 2
1st half of glycolysis (5 reactions): Glucose priming get glucose ready to split phosphorylate glucose molecular rearrangement split destabilized glucose P O CH 2 C O CH 2 OH NAD + Glucose 1 hexokinase Glucose 6-phosphate 3 phosphofructokinase 4,5 aldolase isomerase Dihydroxyacetone phosphate 1,3-Bisphosphoglycerate (BPG) 2 P i 6 glyceraldehyde 3-phosphate dehydrogenase phosphoglucose isomerase Fructose 6-phosphate Fructose 1,6-bisphosphate P i Glyceraldehyde 3 -phosphate (G3P) NAD + 1,3-Bisphosphoglycerate (BPG) P P O O CH 2 OH O CH 2 CH 2 CH 2 H C CHOH O O CH 2 O CHOH O O O CH 2 O O O P CH 2 OH CH 2 O P P P P
2nd half of glycolysis (5 reactions): Energy Harvest production G3P donates H oxidizes the sugar reduces NAD + NAD + production G3P pyruvate PEP sugar donates P substrate level phosphorylation Payola! Finally some! NAD + 3-Phosphoglycerate (3PG) 2-Phosphoglycerate (2PG) H 2 O 7 phosphoglycerate kinase 8 phosphoglyceromutase 9 enolase Phosphoenolpyruvate (PEP) DHAP P-C-C-C Pyruvate P i 6 10 pyruvate kinase G3P C-C-C-P P i 3-Phosphoglycerate (3PG) 2-Phosphoglycerate (2PG) Phosphoenolpyruvate (PEP) Pyruvate H 2 O NAD + O - C CHOH CH 2 O P O - C O H C O CH 2 OH O - C O C O CH 2 O - C O C O CH 3 P P
Substrate-level Phosphorylation: In the last steps of glycolysis, where did the P come from to make? the sugar substrate (PEP) P is transferred from PEP to kinase enzyme H 2 O 9 enolase Phosphoenolpyruvate (PEP) Pyruvate 10 pyruvate kinase Phosphoenolpyruvate (PEP) Pyruvate H 2 O O - C O C O CH 2 O - C O C O CH 3 P I get it! The P i came directly from the substrate!
Energy accounting of glycolysis: 2 2 Net gain = 2 + 2 some energy investment (-2 ) small energy return (4 + 2 ) 1 6C sugar 2 3C sugars glucose pyruvate 6C 2x 3C 4 4 2 NAD + 2 But glucose has so much more to give! All that work! And that s all I get?
Is that all there is? Not a lot of energy So why does glycolysis still take place? for 1 billon years + this is how life on Earth survived no O 2 = slow growth, slow reproduction only harvest 3.5% of energy stored in glucose more carbons to strip off = more energy to harvest O 2 O 2 O 2 O 2 O 2 glucose pyruvate 6C 2x 3C Hard way to make a living!
But can t stop there! DHAP G3P raw materials products NAD + + 1,3-BPG P i P i 6 P i P i 1,3-BPG NAD + + Glycolysis 3-Phosphoglycerate (3PG) 7 8 3-Phosphoglycerate (3PG) glucose + 2 + 2P i + 2 NAD + 2 pyruvate + 2 + 2 Going to run out of NAD + without regenerating NAD +, energy production would stop! another molecule must accept H from so NAD + is freed up for another round 2-Phosphoglycerate (2PG) H 2 O Phosphoenolpyruvate (PEP) Pyruvate 9 10 2-Phosphoglycerate (2PG) Phosphoenolpyruvate (PEP) Pyruvate H 2 O
How is recycled to NAD +? Another molecule must accept H from H 2 O with oxygen aerobic respiration NAD + pyruvate without oxygen anaerobic respiration fermentation CO 2 recycle O 2 acetyl-coa NAD + lactate acetaldehyde NAD + which path you use depends on who you are Krebs cycle lactic acid fermentation ethanol alcohol fermentation
Fermentation (anaerobic): Bacteria, yeast pyruvate ethanol + CO 2 3C 2C 1C NAD + beer, wine, bread Animals, some fungi pyruvate lactic acid 3C 3C NAD + back to glycolysis back to glycolysis cheese, anaerobic exercise (no O 2 )
Alcohol Fermentation: pyruvate ethanol + CO 2 3C 2C 1C NAD + back to glycolysis Dead end process at ~12% ethanol, kills yeast can t reverse the reaction recycle bacteria yeast Count the carbons!
Lactic Acid Fermentation: pyruvate lactic acid 3C 3C NAD + Reversible process once O 2 is available, lactate is converted back to pyruvate by the liver O 2 back to glycolysis recycle animals some fungi Count the carbons!
Pyruvate is a branching point: Pyruvate O 2 O 2 fermentation anaerobic respiration mitochondria Krebs cycle aerobic respiration
What s the point? The point is to make!
And how do we do that? synthase set up a H + gradient allow H + to flow through synthase powers bonding of P i to + P i But Have we done that yet? + P H + H + H + H + H + H + H + H + H +
NO! There s still more to my story! Any Questions?