Cellular Respiration Cellular Respiration Harvesting Chemical Energy ATP

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

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-

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-

Coupling oxidation & reduction  REDOX reactions in respiration  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 O

Energy Transfer  Substrate level phosphorylation  Oxidative phosphorylation

Substrate Level Phosphyralation  ATP is formed directly in an enzyme- catalyzed reaction  Phosphate containing group transfers a phosphate directly to ADP  30.5 kJ/mol of potential energy is also transferred

Substrate Level Phosphorylation 1) Occurs in glycolysis & Krebs cycle 2) Energy and phosphate are transferred to ADP using an enzyme, to form ATP. 3) PEP (phosphoenolpyruvate) is oxidized. 4) Whereas ADP is reduced. 5) ATP has gained Free Energy from PEP. ATP can now do work.

Oxidative Phosphorylation  ATP is formed indirectly  Involves a number of sequential redox reactions  Oxygen is the final electron acceptor  More complex  More ATP generated

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! How efficient! Build once, use many ways H like $$ in the bank

Oxidative Phosphorylation, NAD+  Nicotinamide adenine dinucleotide, NAD+  Coenzyme  Vitamin B3  Improvements in energy functions  Increasing NAD+ increases availability of these molecules for metabolism  Found in various meats, peanuts and sunflower seeds

Oxidative Phosphorylation, FAD Flavin adenine dinucleotide, FAD  Coenzyme  Built from riboflavin  Vitamin B2  Found in meats (liver, kidney & heart), almonds, mushrooms, soybean, green leafy vegetables  Also reduced by two hydrogen atoms  Reduced form FADH 2  In one reaction of the Krebs cycle

NADH and FADH2  Act as mobile energy carriers  Energy harvesting reactions  Eventually transfer most of their energy to ATP molecules

Oxidative Phosphorylation  Begins with nicotinamide adenine dinucleotide (NAD+)  Removes 2H atoms from portion of original glucose  Electrons are passed from the NADH to dehydrogenase  NADH becomes oxidized Dehydrogenase NADH 2 ee NAD+

Oxidative Phosphorylation  Occurs in:  One reaction of glycolysis  During pyruvate oxidation  Three reactions of Krebs cycle

Energy Transfer  Goal is to trap energy  Substrate level phosphorylation  ATP is formed by enzyme catalyzed reaction  6 ATP made per glucose molecule  Oxidative phosphorylation  Many redox reactions form ATP indirectly  More ATP (30) produced per glucose molecule  Forms reduced coenzymes NADH and FADH 2 that will eventually transfer their free energy to ATP

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

Glycolysis and Cancer

Cellular Respiration Stage 1: Glycolysis

Glycolysis glucose      pyruvate 2x2x 6C3C In the cytosol? Why does that make evolutionary sense? That’s not enough ATP for me!  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

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 You mean we’re related? Do I have to invite them over for the holidays? Enzymes of glycolysis are “well-conserved”

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

 DEMO

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  split destabilized glucose

2nd half of glycolysis (5 reactions) Payola! Finally some ATP! 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  ATP production  G3P    pyruvate

Regulation of Glycolysis and Cancer

Glycolysis summary net yield 4 ATP ENERGY INVESTMENT ENERGY PAYOFF G3P C-C-C-P NET YIELD like $$ in the bank -2 ATP

Substrate-level PhosphorylationPhosphorylation I get it! The P i came directly from the substrate! 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? ATP

Energy accounting of glycolysis  Net gain =  some energy investment (-2 ATP)  small energy return (4 ATP + 2 NADH)  1 6C sugar  glucose      pyruvate 2x2x 6C3C All that work! And that’s all I get? But glucose has so much more to give!

Cellular Respiration Stage 2: Citric Acid Cycle or Krebs Cycle

pyruvate       CO 2 Glycolysis is only the start  Glycolysis  Pyruvate has more energy to yield 2x2x 6C3C glucose      pyruvate 3C1C

Cellular respiration

pyruvate    acetyl CoA + CO 2 Oxidation of pyruvate NAD 3C2C 1C [ 2x ]  releases  reduces  produces

Citric Acid cycle 1937 | 1953 Hans Krebs

citrate acetyl CoA Count the carbons! pyruvate x2x2 oxidation of sugars This happens twice for each glucose molecule

6C 5C citrate acetyl CoA Count the electron carriers! pyruvate reduction of electron carriers This happens twice for each glucose molecule x2x2 CO 2 NADH

What’s the point?

Electron Carriers = Hydrogen Carriers What’s so important about electron carriers? H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP ADP + P i

Energy accounting of Citric Acid cycle Net gain= 1 ADP1 ATP ATP 2x 4 NAD + 1 FAD4 NADH + 1 FADH 2 pyruvate          CO 2 3C 3x3x 1C

Value of Citric Acid cycle?  If the yield is only 2 ATP then how was the Citric Acid cycle an adaptation? like $$ in the bank

 The Second Law of Thermodynamics states that spontaneous processes tend to increase the entropy (disorder) of the universe. Why would this law favor a glucose molecule being broken down?  The First Law of Thermodynamics states that energy is neither created or destroyed in any process, including chemical reactions. Looking at the big picture of life, and assuming energy used by organisms comes from the sun, how does ATP production by cellular respiration obey the First Law?