Cellular Respiration (continued) Stage IV: Electron Transport Chain & Chemiosmosis

Recall... C6H12O6 + O2 6 CO2 + 6 H2O + 36 ATP So far, in stages 1-3 (Glycolysis, Pyruvate Oxidation, and the Krebs Cycle) we have: - broken down C6H12O6 - produced 6 CO2 - produced 4 (net) ATP - produced 10 NADH - produced 2 FADH2 These coenzymes will now go to Stage 4 to transfer energy to ATP

# ATP so far 2 from glycolysis 2 from Krebs Cycle 4 Total (All via substrate level phosphorylation)

Total # of Reduced Co-enzymes 2 NADH from glycolysis 2 NADH from pyruvate oxidation 6 NADH from Krebs cycle 10 NADH total and 2 FADH2 from Kreb cycle

Stage and Location 1. Glycolysis: in the cytoplasm 2. Pyruvate Oxidation: in the mitochondrial matrix 3. Krebs Cycle: in the mitochondrial matrix 4. ETC & Chemiosmosis: within the inner mitochondrial membrane

Co-enzymes & Stage IV All the reduced co-enzymes that have been produced will be used in the next stage of cellular respiration (the electron transport chain) which occurs in the mitochondrial matrix However, the 2 NADHs made in glycolysis are in the cytoplasm

The 2 NADH made in glycolysis in the cytoplasm cannot enter the matrix A “shuttle” will take its electrons and transfer it to a FAD to produce FADH2 This is the glycerol-phosphate shuttle

The Glycerol Phosphate Shuttles The NADH is oxidized by the shuttle, turning into NAD+ NAD+ can be reused in glycolysis The shuttle brings the electrons into the matrix They reduce FAD into FADH2 So, there are actually 8 NADH and 4 FADH2 molecules available for Stage 4 (the ETC and Chemiosmosis)

Stage 4: Electron Transport Chain & Chemiosmosis Occurs in the cristae (the folds of the inner mitochondrial membrane) Folds allow for more surface area NADH and FADH2 will transfer their hydrogen atom electrons

Electron Transport Chain (ETC) A series of compounds (mostly proteins) within the inner mitochondrial membrane. They are arranged in order of increasing electronegativity with the weakest at the beginning of the chain. NADH cytochrome Deyhydrogenase oxidase WEAKEST ATTRACTOR STRONGEST ATTRACTOR OF ELECTRONS OF ELECTRONS Increasing eletronegativity

Protein complex Coenzyme is oxidized FADH2 transfers its electrons to Q – not NADH dehydrogenase

Through a series of redox reactions, 2 electrons from each NADH and FADH2 molecule get passed from compound to compound in the ETC chain always moving to the more electronegative compound So each component is reduced, and then oxidized. During the process energy is released (as the é move to more stable compounds)

Some of that energy is lost as heat The rest of the energy is used to move protons (H+ ions) from the matrix to the intermembrane space. The H+ move through proton pumps that are in the 3 membrane associated proteins The last é acceptor is oxgyen (which is very electronegative ) from the matrix

Oxygen combines with the electrons and hydrogen ions to make water ½ (O2) + 2 é + 2 H+ H2O From the matrix from the ETC from the matrix Oxygen combines with the electrons and hydrogen ions to make water (The reaction is catalyzed by the last protein complex – cytochrome oxidaze)

The electron transport process is highly exgergonic Some of the energy was used to pump H+ into the intermembrane space This energy is now stored in the electrochemical gradient of the inner mitochondrial membrane. It will be used to synthesize ATP in CHEMIOSMOSIS

Chemiosmosis During ETC, H+ accumulated in the intermitochondrial membrane This creates an electronchemical gradient which creates a potential difference across the inner mito membrane The energy stored in the gradient produces a proton-motive force (PMF)

The H+ can’t move back into the matrix on their own- they go through a proton channel called ATP synthase (also called ATPase) As the H+ move through ATPase, the energy from the electrochemical gradient drives the synthesis or ATP from ADP and a free phosphate group This is oxidative phosphorylation because the energy used to drive ATP synthesis came from the redox reactions of the ETC!

10 NADH: 2 glycolysis 2 FADH2 = 4 ATP 2 pyruvate oxidation = 6 ATP Each NADH will make 3 ATP Each FADH2 will make 2 ATP Remember... We made: 10 NADH: 2 glycolysis 2 FADH2 = 4 ATP 2 pyruvate oxidation = 6 ATP 6 Krebs Cycle = 18 ATP 2 FADH2: 2 Krebs = 4 ATP Chemiosmosis Total: 32 ATP 2 ATP + 2 ATP + 32 ATP = 36 ATP from glycolysis from Krebs from chemiosmosis

The continual production of ATP requires maintenance of H+ reservoir H+ reservoir requires movement of é through ETC ETC is dependent of having O2 as the final é acceptor

If there is no O2, then the ETC becomes “clogged” with é and H+ won’t be pumped into intermembrane space Chemiosmosis will not occur and ATP won’t be made NADH and FADH2 cannot oxidize Therefore, only glycolysis would take place (because NADH and FADH2 needed for pyruvate oxidation and Krebs)

Animations http://glencoe.mheducation.com/sites/000329 2010/student_view0/chapter7/animations_and _videos.html