2. Cellular Respiration Harvesting Chemical Energy ATP

3. Harvesting stored energy Energy is stored in organic molecules – carbohydrates, fats, proteins Heterotrophs eat these organic molecules  food

4. Harvesting stored energy Glucose is the model – catabolism of glucose to produce ATP C 6 H 12 O 6 6O 2 ATP6H 2 O6CO 2  + ++ CO 2 + H 2 O + heat fuel (carbohydrates) COMBUSTION = making a lot of heat energy by burning fuels in one step RESPIRATION = making ATP (& some heat) by burning fuels in many small steps CO 2 + H 2 O + ATP (+ heat) ATP glucose glucose + oxygen  energy + water + carbon dioxide respiration O2O2 O2O2 + heat enzymes ATP

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 ATP e-e- ++ e-e- +– loses e-gains e-oxidizedreduced oxidationreduction redox e-e-

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 p e + H + H +– loses e-gains e-oxidizedreduced oxidationreduction C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction H e-e-

7. Coupling oxidation & reduction REDOX reactions in respiration – release energy as they breakdown organic molecules break C-C bonds strip off electrons from C-H bonds by removing H atoms – C 6 H 12 O 6  CO 2 = the fuel has been oxidized electrons attracted to more electronegative atoms – in biology, the most electronegative atom? – O 2  H 2 O = oxygen has been reduced – couple REDOX reactions & use the released energy to synthesize ATP C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction O2O2

8. Oxidation & reduction Oxidation – removing H – loss of electrons – releases energy – exergonic Reduction – adding H – gain of electrons – stores energy – endergonic C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction

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

10. Overview of cellular respiration 4 metabolic stages – Anaerobic respiration 1. Glycolysis – respiration without O 2 – in cytosol – Aerobic respiration – respiration using O 2 – in mitochondria 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain C 6 H 12 O 6 6O 2 ATP6H 2 O6CO 2  +++ (+ heat )

11. Glycolysis glucose      pyruvate 2x2x 6C3C 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 only 2 ATP for every 1 glucose – occurs in cytosol

12. 10 reactions – convert glucose (6C) to 2 pyruvate (3C) – produces: 4 ATP & 2 NADH – consumes: 2 ATP – net yield: 2 ATP & 2 NADH glucose C-C-C-C-C-C 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 Overview DHAP = dihydroxyacetone phosphate G3P = glyceraldehyde-3-phosphate ATP 2 ADP 2 ATP 4 ADP 4 NAD + 2 2Pi2Pi enzyme 2Pi2Pi 2H2H 2

13. Glycolysis summary endergonic invest some ATP exergonic harvest a little ATP & a little NADH net yield 2 ATP 2 NADH 4 ATP ENERGY INVESTMENT ENERGY PAYOFF G3P C-C-C-P NET YIELD -2 ATP

14. PiPi 3 6 4,5 ADP NAD + Glucose hexokinase phosphoglucose isomerase phosphofructokinase Glyceraldehyde 3 -phosphate (G3P) Dihydroxyacetone phosphate Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate isomerase glyceraldehyde 3-phosphate dehydrogenase aldolase 1,3-Bisphosphoglycerate (BPG) 1,3-Bisphosphoglycerate (BPG) 1 2 ATP ADP ATP NADH NAD + NADH PiPi CH 2 CO CH 2 OH PO CH 2 OP O CHOH C CH 2 OP O CHOH CH 2 OP O OP O P O H CH 2 OH O CH 2 P O O CH 2 OH P O 1st half of glycolysis (5 reactions) Glucose “priming”  get glucose ready to split  phosphorylate glucose  molecular rearrangement  split destabilized glucose

15. 2nd half of glycolysis (5 reactions) 7 8 H2OH2O 9 10 ADP ATP 3-Phosphoglycerate (3PG) 3-Phosphoglycerate (3PG) 2-Phosphoglycerate (2PG) 2-Phosphoglycerate (2PG) Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) Pyruvate phosphoglycerate kinase phosphoglycero- mutase enolase pyruvate kinase ADP ATP ADP ATP ADP ATP H2OH2O CH 2 OH CH 3 CH 2 O-O- O C PH CHOH O-O- O-O- O-O- C C C C C C P P O O O O O O CH 2 NAD + NADH NAD + NADH Energy Harvest G3P C-C-C-P PiPi PiPi 6 DHAP P-C-C-C – NADH production G3P donates H oxidizes the sugar reduces NAD + NAD +  NADH – ATP production G3P    pyruvate PEP sugar donates P – “substrate level phosphorylation” ADP  ATP

16. Substrate-level Phosphorylation P is transferred from PEP to ADP kinase enzyme ADP  ATP H2OH2O 9 10 Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) Pyruvate enolase pyruvate kinase ADP ATP ADP ATP H2OH2O CH 3 O-O- O C O-O- C C C P O O O CH 2 In the last steps of glycolysis, where did the P come from to make ATP? – the sugar substrate (PEP) ATP

17. Energy accounting of glycolysis Net gain = 2 ATP + 2 NADH – some energy investment (-2 ATP) – small energy return (4 ATP + 2 NADH) 1 6C sugar  2 3C sugars 2 ATP2 ADP 4 ADP glucose      pyruvate 2x2x 6C3C ATP 4 2 NAD + 2

18. 7 8 H2OH2O 9 10 ADP ATP 3-Phosphoglycerate (3PG) 3-Phosphoglycerate (3PG) 2-Phosphoglycerate (2PG) 2-Phosphoglycerate (2PG) Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) Pyruvate ADP ATP ADP ATP ADP ATP H2OH2O NAD + NADH NAD + NADH PiPi PiPi 6 But can’t stop there! Going to run out of NAD + – without regenerating NAD +, energy production would stop! – another molecule must accept H from NADH so NAD + is freed up for another round PiPi NAD + G3P 1,3-BPG NADH NAD + NADH PiPi DHAP raw materials  products

19. NADH pyruvate acetyl-CoA lactate ethanol NAD + NADH NAD + NADH CO 2 acetaldehyde Krebs cycle lactic acid fermentation with oxygen aerobic respiration without oxygen anaerobic respiration “fermentation” How is NADH recycled to NAD + ? Another molecule must accept H from NADH recycle NADH which path you use depends on who you are… alcohol fermentation