Chapter 9.3 Cellular Respiration: Electron Transport Chain

Cellular Respiration

There’s got to be a better way! ATP accounting so far… Glycolysis  2 ATP Oxidation of Pyruvate  ~ 0 ATP Kreb’s cycle  1 ATP [x2] Life takes a lot of energy to run, need to extract more energy than just 4 ATP! There’s got to be a better way! What was the point again?

There IS a better way! Electron Transport Chain series of molecules built into inner mitochondrial membrane mostly integral transport proteins transport of electrons down ETC linked to ATP synthesis yields ~ additional 34 ATP from 1 glucose! only when in presence of O2 (aerobic) That’s more like it!

Form fits function! Mitochondria Double membrane outer membrane inner membrane highly folded cristae* fluid-filled space between membranes = intermembrane space matrix (mitochondrial matrix) central fluid-filled space Form fits function!

Electron Transport Chain

Remember the NADH/FADH2? pyruvate oxidation & Kreb’s cycle 8 NADH 2 FADH2 Glycolysis 3GP (PGAL) 2 NADH

Electron Transport Chain NADH passes electrons to ETC H cleaved off NADH & FADH2 (oxidized) electrons stripped from H atoms  H+ (H ions) electrons passed from one electron carrier to next in mitochondrial membrane (ETC) transport proteins in membrane pump H+ across inner membrane to intermembrane space as electrons move AP Link—Ch 07: Proton Pumping Oxidation refers to the loss of electrons to any electron acceptor, not just to oxygen. Uses exergonic flow of electrons through ETC to pump H+ across membrane.

Electrons flow downhill downhill? Uh, what does that mean? AP Link—Ch 07: John Kyrk’s ETC Pumping H+ across membrane … what is energy to fuel that? Can’t be ATP! that would cost you what you want to make! Its like cutting off your leg to buy a new pair of shoes. :-( Flow of electrons powers pumping of H+ O2 is 2 oxygen atoms both looking for electrons O2

Electrons flow downhill Electrons move in steps from carrier to carrier downhill to O2 each carrier more electronegative controlled oxidation controlled release of energy Like a game of hot potato… with each kid in line liking fries more and more! AP Link—Ch 07: ETC (TSOB) Electrons move from molecule to molecule until they combine with O & H ions to form H2O It’s like pumping water behind a dam -- if released, it can do work

ATP ATP Why the build up H+? ATP ATP synthase ATP ADP + Pi  ATP OK! I get the point! Can I take my fingers out of my ears? Wait a second… I don’t even have any bloody arms! What the heck… ATP synthase enzyme in inner membrane of mitochondria ADP + Pi  ATP only channel permeable to H+ H+ flow down concentration gradient = provides energy for ATP synthesis “proton-motive” force molecular power generator! flow like water over water wheel flowing H+ cause change in shape of ATP-synthase enzyme powers bonding of Pi to ADP H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ ATP ATP ATP ATP ATP ATP ATP ATP ATP ATP ATP ATP ATP ATP ATP ATP ATP ATP

ATP synthesis Chemiosmosis couples ETC to ATP synthesis build up of H+ gradient just so H+ could flow through ATP synthase enzyme to build ATP So THAT’S the point! AP Link—Ch 07: Chemiosmosis

Peter Mitchell 1961 | 1978 Proposed chemiosmotic hypothesis revolutionary idea at the time “proton motive force” 1920-1992

Cellular Respiration So here it all is!

Summary of Cellular Respiration C6H12O6 6O2 6CO2 6H2O ~36 ATP  + Where did the glucose come from? Where did the O2 come from? Where did the CO2 come from? Where did the H2O come from? Where did the ATP come from? What else is produced that is not listed above? Why do we breathe…? AP Movie—Ch 07: Cell Respiration Animation Where did the glucose come from? from food eaten Where did the O2 come from? breathed in Where did the CO2 come from? oxidized carbons cleaved off of the sugars Where did the H2O come from? from O2 after it accepts electrons in ETC Where did the ATP come from? mostly from ETC What else is produced that is not listed in this equation? NAD, FAD, heat!

Why do we breathe? What is the final electron acceptor in electron transport chain? O2 So what happens if O2 unavailable? ETC backs up ATP production ceases cells run out of energy and you die! What if you have a chemical that punches holes in the inner mitochondrial membrane? Whoops!

ATP Any Questions? The Point is to Make ATP! What’s the point? AP Movie—Ch 07: Cell Respiration Animated The Point is to Make ATP! Any Questions?