Cellular Respiration Stage 4: Electron Transport Chain 2006-2007

Cellular respiration

What’s the point? The point is to make ATP! ATP 2006-2007

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

That sounds more like it! There is a better way! Electron Transport Chain series of proteins built into inner mitochondrial membrane along cristae transport proteins & enzymes transport of electrons down ETC linked to pumping of H+ to create H+ gradient yields ~36 ATP from 1 glucose! only in presence of O2 (aerobic respiration) That sounds more like it! O2

ETC Review the video for electron transport and answer the following questions: Electron Transport Video Where do the electrons for the ETC come from? Where is this process taking place? How do the electrons get shuttled down the ETC? How is electronegativity involved? (you’ll have to think about this one, they do not explain this in the video) What molecule is the final acceptor of the electrons? What is the byproduct that is generated during the ETC? The ETC does not generate ATP. What is it’s purpose?

Oooooh! Form fits function! Mitochondria Double membrane outer membrane inner membrane highly folded cristae enzymes & transport proteins intermembrane space fluid-filled space between membranes Oooooh! 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? glucose Krebs cycle Glycolysis G3P 2 NADH 8 NADH 2 FADH2 Time to break open the piggybank!

Electron Transport Chain Building proton gradient! NADH  NAD+ + H 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 Why does FADH2 drop its electrons on a different initial carrier? 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+ (protons) electrons passed from one electron carrier to next in mitochondrial membrane (ETC) flowing electrons = energy to do work transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane space NAD+ Q C NADH H2O H+ e– 2H+ + O2 FADH2 1 2 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD 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. H+ TA-DA!! Moving electrons do the work! H+ H+ H+ ADP + Pi ATP

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

Electrons flow downhill Electrons move in steps from carrier to carrier downhill to oxygen each carrier more electronegative controlled oxidation controlled release of energy make ATP instead of fire! 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

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

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 Chemiosmosis is the diffusion of ions across a membrane. More specifically, it relates to the generation of ATP by the movement of hydrogen ions across a membrane. Hydrogen ions (protons) will diffuse from an area of high proton concentration to an area of lower proton concentration. Peter Mitchell proposed that an electrochemical concentration gradient of protons across a membrane could be harnessed to make ATP. He likened this process to osmosis, the diffusion of water across a membrane, which is why it is called chemiosmosis. So that’s the point!

Chemiosmotic Model ATP Synthase video

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

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

ATP production Phosphorylation Substrate level phophorylation Addition of phosphate group to an organic molecule Substrate level phophorylation Phosphate is added as a result of enzymatic reaction Oxidative phosphorylation

ATP produced GLUCOSE

2 ATP GLUCOSE 2 ATP produced directly GLYCOLYSIS

38 ATP 16 ATP 34 ATP 8 ATP 14 ATP 2 ATP 2 NADH 2 NADH 6 NADH 2 FADH2 GLUCOSE 2 ATP produced directly GLYCOLYSIS 6 ATP through electron transport + 2 NADH PYRUVIC ACID 6 ATP through electron transport + 2 NADH 2 ATP produced directly + ACETYL CoA 18 ATP through electron transport + KREBS CYCLE 6 NADH 4 ATP through electron transport + 2 FADH2

Learning Check Which molecules are being oxidized and reduced in each step of cell resp (Hint think about your starting materials, end products, and where the e-/H ions are going) Glycolysis? Krebs? ETC? Overall? (write the formula for cell resp)

January 9, 2012 BellRinger Objective Homework Previous Slide Develop a visual model to review the important steps of cellular respiration Explore ways to determine the rate of cellular resp in living organisms Homework Cell Respiration Prelab Grade your own Break FR- due Wed

Video of Cellular Respiration ~40 ATP Video of Cellular Respiration + + 2 ATP 2 ATP ~36 ATP

Summary of cellular respiration C6H12O6 6O2 6CO2 6H2O ~40 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 breathe? 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 (Krebs Cycle) Where did the CO2 go? exhaled 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!

Other Nutrients Humans gain more energy from oxidation of fatty acids than glucose Lipids contain 9 kcal per gram Lipids are broken down and glycerol enters glycolysis; fatty acids are converted to acetyl CoA and enter the citric acid cycle

Other Nutrients Proteins are broken down into amino acids Amino acids are deaminated (the amino acids are removed) The remaining carbon chain enters at various points Proteins contain about 4 kcal per gram

Challenge Create a visual model that explains all three steps of cellular respiration. You can draw it or act it out Keep track of what happens to: The carbon molecules that start off in glucose The reduction of oxygen The electrons that are transferred by the electron carriers The hydrogen ions that create the chemiosmotic gradient The production of ATP

What’s the point? The point is to make ATP! ATP 2006-2007

Testing it out What variables would effect the rate at which respiration occurs? How might you set up an experiment to test this? What could you do to measure the rate of repspiration?