Cellular Respiration Stage 2 3 Oxidation of Pyruvate

Cellular Respiration Stage 2 & 3: Oxidation of Pyruvate Krebs Cycle AP Biology 2006 -2007

Glycolysis is only the start § Glycolysis glucose pyruvate 6 C 2 x 3 C § Pyruvate has more energy to yield u u u 3 more C to strip off (to oxidize) if O 2 is available, pyruvate enters mitochondria enzymes of Krebs cycle complete the full oxidation of sugar to CO 2 pyruvate CO 2 AP Biology 3 C 1 C

Cellular respiration AP Biology

Mitochondria — Structure § Double membrane energy harvesting organelle u u smooth outer membrane highly folded inner membrane § cristae u intermembrane space § fluid-filled space between membranes u matrix § inner fluid-filled space u u DNA, ribosomes enzymes What cells would have AP Biology a lot of mitochondria? outer intermembrane inner space membrane cristae matrix mitochondrial DNA

Mitochondria – Function Oooooh! Form fits function! Dividing mitochondria Membrane-bound proteins Who else divides like that? Enzymes & permeases What does this tell us about the evolution of eukaryotes? Endosymbiosis! AP Biology Advantage of highly folded inner membrane? More surface area for membranebound enzymes & permeases

Oxidation of pyruvate § Pyruvate enters mitochondria [ 2 x pyruvate acetyl Co. A + CO 2 3 C 2 C 1 C NAD Where does the CO 2 go? Exhale! 3 step oxidation process u releases 1 CO 2 (count the carbons!) u reduces 2 NADH (moves e-) u produces acetyl Co. A u § Acetyl Co. A enters Krebs cycle AP Biology ]

Pyruvate oxidized to Acetyl Co. A reduction NAD+ Pyruvate C-C-C [ CO 2 Coenzyme A oxidation Acetyl Co. A C-C 2 x Yield = 2 C sugar + NADH + CO 2 AP Biology ]

Krebs cycle 1937 | 1953 § aka Citric Acid Cycle in mitochondrial matrix u 8 step pathway u Hans Krebs § each catalyzed by specific enzyme 1900 -1981 § step-wise catabolism of 6 C citrate molecule § Evolved later than glycolysis u AP Biology does that make evolutionary sense? § bacteria 3. 5 billion years ago (glycolysis) § free O 2 2. 7 billion years ago (photosynthesis) § eukaryotes 1. 5 billion years ago (aerobic respiration = organelles mitochondria)

Count the carbons! pyruvate 3 C 2 C 6 C 4 C This happens twice for each glucose molecule AP Biology acetyl Co. A citrate x 2 4 C 6 C oxidation of sugars CO 2 5 C 4 C 4 C 4 C CO 2

Count the electron carriers! pyruvate 3 C FADH 2 AP Biology 6 C 4 C NADH This happens twice for each glucose molecule 2 C 4 C 4 C acetyl Co. A citrate x 2 NADH 6 C reduction of electron carriers 4 C ATP CO 2 4 C CO 2 NADH 5 C CO 2 NADH

Whassup? So we fully oxidized glucose C 6 H 12 O 6 CO 2 & ended up with 4 ATP! AP Biology What’s the point?

Electron Carriers = Hydrogen Carriers H+ § Krebs cycle produces large quantities of electron carriers NADH u FADH 2 u go to Electron Transport Chain u AP Biology What’s so important about electron carriers? H+ H+ H+ H+ ADP + Pi ATP H+

Energy accounting of Krebs cycle 4 NAD + 1 FAD 4 NADH + 1 FADH 2 2 x pyruvate CO 2 3 x 1 C 3 C 1 ADP 1 ATP Net gain = 2 ATP = 8 NADH + 2 FADH 2 AP Biology

Value of Krebs cycle? § If the yield is only 2 ATP then how was the Krebs cycle an adaptation? u value of NADH & FADH 2 § electron carriers & H carriers w reduced molecules move electrons w reduced molecules move H+ ions § to be used in the Electron Transport Chain like $$ in the bank AP Biology

H+ And how do we do that? H+ H+ § Set up a H+ gradient allow H+ to flow through ATP synthase u powers bonding of Pi to ADP u ADP + Pi ATP ADP + P ATP H+ AP Biology But… Have we done that yet?

NO! The final chapter to my story is next! Any Questions? AP Biology

Cellular Respiration Stage 4: Electron Transport Chain AP Biology 2006 -2007

Electron Transport Chain Building proton gradient! NADH NAD+ + H e p intermembrane space H+ H+ H e- + H+ C e– NADH H FADH 2 NAD+ NADH dehydrogenase inner mitochondrial membrane e– Q AP Biology H+ e– H FAD 2 H+ + 12 O 2 cytochrome bc complex H 2 O cytochrome c oxidase complex mitochondrial matrix What powers the proton (H+) pumps? …

Stripping H from Electron Carriers § NADH passes electrons to ETC u u H cleaved off NADH & FADH 2 electrons stripped from H atoms H+ (protons) electrons passed from one electron carrier to next in mitochondrial membrane (ETC) transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane space H+ TA-DA!! Moving electrons do the work! H+ H+ H+ H H+ C e– NADH AP Biology H+ Q e– FADH 2 FAD NAD+ NADH dehydrogenase e– 1 2 H+ + cytochrome bc complex 2 O 2 H 2 O cytochrome c oxidase complex ADP + Pi ATP H+

But what “pulls” the electrons down the ETC? O 2 AP Biology electrons flow downhill to O 2 oxidative phosphorylation

Electrons flow downhill § Electrons move in steps from carrier to carrier downhill to O 2 each carrier more electronegative u controlled oxidation u controlled release of energy u make ATP instead of fire! AP Biology

“proton-motive” force We did it! § Set up a H+ § § H+ H+ gradient Allow the protons to flow through ATP synthase Synthesizes ATP ADP + Pi ATP Are we there yet? AP Biology H+ H+ H+ ADP + Pi ATP H+

Chemiosmosis § The diffusion of ions across a membrane u build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP Chemiosmosis links the Electron Transport Chain to ATP synthesis So that’s the point! AP Biology

Pyruvate from cytoplasm Inner + mitochondrial H membrane H+ Intermembrane space Electron transport C system Q NADH Acetyl-Co. A 2. Electrons provide energy 1. Electrons are harvested to pump protons and carried to the transport across the system. membrane. - NADH Krebs cycle e- e FADH 2 e- 3. Oxygen joins with protons to form water. ATP Mitochondrial matrix AP Biology e- H 2 O 1 O 2 +2 2 H+ O 2 H+ CO 2 2 H+ 32 ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. H+ ATP synthase

Cellular respiration 2 ATP AP Biology ~4 0 A + ~2 ATP + ~34 ATP TP

Summary of cellular respiration C 6 H 12 O 6 + 6 O 2 § § § § 6 CO 2 + 6 H 2 O + ~40 ATP Where did the glucose come from? Where did the O 2 come from? Where did the CO 2 go? Where did the H 2 O come from? Where did the ATP come from? What else is produced that is not listed in this equation? § Why do we breathe? AP Biology

Taking it beyond… § What is the final H+ H+ H+ C Q e– FADH 2 FAD electron acceptor in NADH 2 H + NAD Electron Transport O 2 Chain? So what happens if O 2 unavailable? § ETC backs up e– + + NADH dehydrogenase § cytochrome bc complex e– 1 2 O 2 H 2 O cytochrome c oxidase complex nothing to pull electrons down chain u NADH & FADH 2 can’t unload H u AP Biology § ATP production ceases § cells run out of energy § and you die!