Stage 4: Electron Transport Chain Cellular respiration Stage 4: Electron Transport Chain

Cellular respiration

A working muscle recycles over 10 million ATPs per second Atp accounting so far … Glycolysis  2 ATP Kreb’s cycle  2 ATP Life takes a lot of energy, need more than 4 ATP! There’s got to be more! I need a lot more ATP! A working muscle recycles over 10 million ATPs per second

There is more! O2 Electron Transport Chain (ETC) Series of proteins build into inner mitochondrial membrane Along cristae Contains transport proteins & enzymes Transport of electrons down ETC are linked to the pumping of H+ ions to create an H+ gradient Yields ~34 ATP per 1 glucose molecule Only occurs in the presence of O2 (aerobic respiration) O2 That’s more like it!

mitochondria Double membrane Outer membrane Inner membrane Highly folded cristae Contains transport proteins & enzymes Intermembrane space Fluid-filled space between membranes Remember: Form fits function!

Electron Transport Chain Inner mitochondrial membrane Intermembrane space C Q NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex Mitochondrial matrix

Remember the electron carriers? Glycolysis --> 2 NADH Kreb’s cycle  8 NADH 2 FADH2 Time to break open the piggybank!

Electron Transport Chain NADH  NAD+ + H Building proton gradient! p e intermembrane space H+ H+ H+ inner mitochondrial membrane H  e- + H+ C Q e– e– e– H FADH2 FAD H 1 2 NADH 2H+ + O2 H2O NAD+ NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex mitochondrial matrix What powers the proton (H+) pumps?…

Stripping H from electron carriers Electron carriers pass electrons & H+ to ETC H cleaved off NADH & FADH2 Electrons stripped from H atoms  H+ Electrons pass from one electron carrier to the next Flowing electrons create energy to do work Transport proteins in membrane pump H+ (protons) across the inner membrane to intermediate space NAD+ Q C NADH H2O H+ e– 2H+ + O2 FADH2 1 2 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD TA-DA!! Moving electrons do the work! H+ ADP + Pi ATP

electrons flow downhill to O2 But what “pulls” the electrons down the ETC? H2O O2 electrons flow downhill to O2 oxidative phosphorylation

Electrons flow downhill Electrons move in steps from carrier to carrier downhill to oxygen Each subsequent carrier is more electronegative Controlled oxidation Controlled release of energy make ATP instead of fire!

We did it! Set up a H+ gradient ADP + Pi Set up a H+ gradient Now need to let protons flow through ATP synthase Synthesis ATP ADP + Pi  ATP Are we there yet? ATP

Chemiosmosis links the Electron Transport Chain to ATP synthesis The diffusion of ions across a membrane 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 Now we’re talking energy! But how much?

ATP Pyruvate from cytoplasm Intermembrane space Inner mitochondrial Electron transport system C Q NADH e- 2. Electrons provide energy to pump protons across the membrane. H+ 1. Electrons are harvested and carried to the transport system. e- Acetyl-CoA NADH e- H2O Krebs cycle e- 3. Oxygen joins with protons to form water. 1 FADH2 O2 2 O2 + 2H+ CO2 H+ ATP ATP H+ ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. ATP synthase Mitochondrial matrix

~38 ATP Cellular respiration 2 ATP 2 ATP ~34 ATP

Summary of cellular respiration C6H12O6 6O2 6CO2 6H2O ~38 ATP  + Where did the glucose come from? Where did the O2 come from? Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the ATP come from? What else is produced that is not listed in this equation? Why do we breath?

cytochrome c oxidase complex If oxygen is missing … What is the final electron acceptor in the ETC? So, what happens if O2 is unavailable? Nothing pulls the electrons down the chain ETC backs up NADH & FADH2 can’t load H+ ATP production stops Cells run out of energy You die! O2 NAD+ Q C NADH H2O H+ e– 2H+ + O2 FADH2 1 2 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD Cyanide attaches to the final electron acceptor (fourth, but only three are shown). By binding to the protein, it can no longer accept electrons and the ETC is stopped … no more ATP are produced.

THAT’S IT! We’re finally done. Any questions?