Cellular Respiration Stage 1: Glycolysis (Ch. 6)

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1 Cellular Respiration Stage 1: Glycolysis (Ch. 6)

2 What s the point? The point is to make!

3 Harvesting stored energy Energy is stored in organic molecules carbohydrates, fats, proteins Heterotrophs eat these organic molecules food digest organic molecules to get raw materials for synthesis fuels for energy

4 respiration Harvesting stored energy Glucose is the model catabolism of glucose to produce glucose + oxygen energy + water + carbon dioxide C 6 H H 2 + 6C 2 + heat CMBUSTIN = making a lot of heat energy by burning fuels in one step fuel arbohydrates) 2 C 2 + H 2 + heat RESPIRATIN = making (& some heat) by burning fuels in many small steps glucose enzymes 2 C 2 + H 2 + (+ heat)

5 How do we harvest energy from fuels? Digest large molecules into smaller ones break bonds & move electrons from one molecule to another as electrons move they carry energy with them that energy is stored in another bond, released as heat or harvested to make loses e- gains e- oxidized reduced e - e - oxidation redox e - reduction

6 How do we move electrons in biology? Moving electrons in living systems electrons cannot move alone in cells electrons move as part of H atom move H = move electrons e p loses e- gains e- oxidized reduced H oxidation oxidation H reduction C 6 H C 2 + 6H 2 + H e - reduction

7 Coupling oxidation & reduction REDX reactions in respiration release energy (break C-C bonds in organics) Strip electrons from C-H bonds: remove H atoms electrons attracted to more electronegative atoms in biology, the most electronegative atom? 2 H 2 = oxygen has been reduced couple REDX reactions & use the released energy to synthesize oxidation 2 C 6 H C 2 + 6H 2 + reduction

8 xidation & reduction xidation adding removing H loss of electrons releases energy exergonic Reduction removing adding H gain of electrons stores energy endergonic oxidation C 6 H C 2 + 6H 2 + reduction

9 Moving electrons in respiration Electron carriers move electrons by shuttling H atoms around NAD + nicotinamide Vitamin B3 niacin P NAD + (reduced) FAD +2 FADH 2 (reduced) H N + C NH 2 + H reduction oxidation like $$ in the bank phosphates P adenine P reducing power! H H N + C NH 2 P ribose sugar carries electrons as a reduced molecule

10 verview of cellular respiration 4 metabolic stages Anaerobic respiration 1. Glycolysis respiration without 2 in cytosol Aerobic respiration respiration using 2 in mitochondria 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain C 6 H H 2 + 6C 2 (+ heat)

11 Glycolysis Breaking down glucose glyco lysis (splitting sugar) glucose pyruvate 6C 2x 3C ancient pathway which harvests energy where energy transfer first evolved In the cytosol? Why does that make evolutionary sense? still is starting point for ALL cellular respiration but it s inefficient generate only 2 for every 1 glucose occurs in cytosol

12 Evolutionary perspective Prokaryotes first cells had no organelles Anaerobic atmosphere life on Earth first evolved without free oxygen ( 2 ) in atmosphere energy had to be captured from organic molecules in absence of 2 Prokaryotes that evolved glycolysis are ancestors of all modern life ALL cells still utilize glycolysis

13 verview 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 ADP NAD + ADP

14 Glycolysis summary ENERGY INVESTMENT endergonic invest some -2 ENERGY PAYFF G3P C-C-C-P 4 exergonic harvest a little & a little like $$ in the bank NET YIELD net yield 2 2

15 1st half of glycolysis (5 reactions) Glucose priming get glucose ready to split phosphorylate glucose molecular rearrangement split destabilized glucose P CH 2 C CH 2 H NAD + ADP 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 ADP Fructose 1,6-bisphosphate P i Glyceraldehyde 3 -phosphate (G3P) NAD + 1,3-Bisphosphoglycerate (BPG) P P CH 2 H CH 2 P CH 2 P CH 2 H CH 2 CH 2 P H C CHH CH 2 P CHH CH 2 P

16 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 ADP Payola! Finally some! NAD + ADP 3-Phosphoglycerate (3PG) 2-Phosphoglycerate (2PG) H 2 7 phosphoglycerate kinase 8 phosphoglyceromutase 9 enolase Phosphoenolpyruvate (PEP) ADP 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 NAD + ADP ADP - C CHH CH 2 P - C H C CH 2 H - C C CH 2 - C C CH 3 P P

17 Energy accounting of glycolysis 2 2 ADP glucose pyruvate 6C 2x 3C 4 ADP 4 2 NAD + 2 But glucose has Net gain = some energy investment (-2 ) small energy return (4 + 2 ) 1 6C sugar 2 3C sugars so much more to give! All that work! And that s all I get?

18 Is that all there is? Not a lot of energy 2 for 1 billon years + this is how life on Earth survived no 2 = slow growth, slow reproduction only harvest 3.5% of energy stored in glucose more carbons to strip off = more energy to harvest 2 glucose pyruvate 6C 2x 3C Hard way to make a living!

19 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 ADP 3-Phosphoglycerate (3PG) 7 8 ADP 3-Phosphoglycerate (3PG) glucose + 2ADP + 2P i + 2 NAD + 2 pyruvate 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 9 Phosphoenolpyruvate (PEP) ADP Pyruvate 10 2-Phosphoglycerate (2PG) Phosphoenolpyruvate (PEP) Pyruvate H 2 ADP

20 How is recycled to NAD +? Another molecule must accept H from with oxygen aerobic respiration pyruvate without oxygen anaerobic respiration fermentation H 2 NAD + C 2 recycle 2 acetyl-coa NAD + lactate acetaldehyde NAD + which path you use depends on who you are Krebs cycle lactic acid fermentation ethanol alcohol fermentation

21 Fermentation (anaerobic) Bacteria, yeast pyruvate ethanol + C 2 3C NAD + beer, wine, bread 2C 1C back to glycolysis Animals, some fungi pyruvate lactic acid 3C 3C NAD + back to glycolysis cheese, anaerobic exercise (no 2 )

22 Lactic Acid Fermentation pyruvate lactic acid 3C NAD + 3C Reversible process once 2 is available, lactate is converted back to pyruvate by the liver 2 back to glycolysis recycle animals some fungi

23 Alcohol Fermentation pyruvate ethanol + C 2 3C NAD + Dead end process at ~12% ethanol, kills yeast can t reverse the reaction 2C 1C back to glycolysis recycle bacteria yeast

24 Pyruvate is a branching point Pyruvate 2 2 fermentation anaerobic respiration mitochondria Krebs cycle aerobic respiration

25 What s the point? The point is to make!