Chapter 15 lecture 4
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The document discusses cellular respiration and the electron transport chain. It explains that: 1) The electron transport chain generates ATP through oxidative phosphorylation by establishing a proton gradient across the inner mitochondrial membrane as electrons are transported from NADH and FADH2 to oxygen. 2) As protons diffuse back through ATP synthase, ATP is synthesized from ADP and inorganic phosphate. This process is called chemiosmosis and allows for the generation of approximately 36 additional ATP molecules per glucose. 3) Peter Mitchell proposed the chemiosmotic hypothesis in 1961 to explain how the electron transport chain is coupled to ATP synthesis.
Chapter 15 lecture 4
- 1. Cellular Respiration Stage 4: Electron Transport Chain 2006-2007
- 3. 2006-2007 What’s the point? The point is to make ATP ! ATP
- 4. 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 ! A working muscle recycles over 10 million ATPs per second There’s got to be a better way! I need a lot more ATP !
- 5. 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 O 2 ( aerobic respiration ) That sounds more like it ! O 2
- 6. Mitochondria Double membrane outer membrane inner membrane highly folded cristae enzymes & transport proteins intermembrane space fluid-filled space between membranes Oooooh ! Form fits function !
- 7. Electron Transport Chain Intermembrane space Mitochondrial matrix Q C NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex Inner mitochondrial membrane
- 8. Remember the Electron Carriers? G3P Glycolysis Krebs cycle 8 NADH 2 FADH 2 2 NADH Time to break open the piggybank ! glucose
- 9. Electron Transport Chain intermembrane space mitochondrial matrix inner mitochondrial membrane NAD + Q C NADH H 2 O H + e – 2H + + O 2 H + H + e – FADH 2 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD e – H H e- + H + NADH NAD + + H H Building proton gradient ! What powers the proton (H + ) pumps?… 1 2 p e
- 10. Stripping H from Electron Carriers Electron carriers pass electrons & H + to ETC 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) flowing electrons = energy to do work transport proteins in membrane pump H + ( protons ) across inner membrane to intermembrane space ATP ADP + P i TA-DA !! Moving electrons do the work ! H + H + H + H + H + H + H + H + H + H + H + H + NAD + Q C NADH H 2 O H + e – 2H + + O 2 H + H + e – FADH 2 1 2 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD e –
- 11. But what “pulls” the electrons down the ETC? electrons flow downhill to O 2 oxidative phosphorylation O 2 H 2 O
- 12. 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 !
- 13. We did it! Set up a H + gradient Allow the protons to flow through ATP synthase Synthesizes ATP ADP + P i ATP ATP Are we there yet? “ proton-motive” force H + ADP + P i H + H + H + H + H + H + H + H +
- 14. 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 Chemiosmosis links the Electron Transport Chain to ATP synthesis So that’s the point !
- 15. Peter Mitchell Proposed chemiosmotic hypothesis revolutionary idea at the time 1961 | 1978 1920-1992 proton motive force
- 16. H + H + O 2 + Q C ATP Pyruvate from cytoplasm Electron transport system ATP synthase H 2 O CO 2 Krebs cycle Intermembrane space Inner mitochondrial membrane 1. Electrons are harvested and carried to the transport system. 2. Electrons provide energy to pump protons across the membrane. 3. Oxygen joins with protons to form water . 2H + NADH NADH Acetyl-CoA FADH 2 ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP . Mitochondrial matrix 2 1 H + H + O 2 H + e - e - e - e - ATP
- 17. Cellular respiration 2 ATP 2 ATP ~36 ATP + + ~40 ATP
- 18. Summary of cellular respiration Where did the glucose come from? Where did the O 2 come from? Where did the CO 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? C 6 H 12 O 6 6O 2 6CO 2 6H 2 O ~40 ATP + + +
- 19. Taking it beyond… What is the final electron acceptor in Electron Transport Chain? ETC backs up nothing to pull electrons down chain NADH & FADH 2 can’t unload H ATP production ceases cells run out of energy and you die ! O 2 So what happens if O 2 unavailable? NAD + Q C NADH H 2 O H + e – 2H + + O 2 H + H + e – FADH 2 1 2 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD e –
- 21. 2006-2007 What’s the point? The point is to make ATP ! ATP
- 22. Respiratory substrates Glucose – primary substrate Lipids & amino acids also can be used Energy values of substrates Carbohydrates - 15.8 kJ/g Lipids - 39.4 kJ/g Protiens - 17.0 kJ/g So then why don’t we use fats for energy, they have the greatest value?
- 23. THE RESPIRATORY QUOTIENT Animal cells obtain energy in the form of ATP by oxidizing food molecules through the process of respiration. Respiration in animal cells depends on oxygen. Electrons from the chemical bonds of the fuel source combine with oxygen and hydrogen ions to form water and carbon dioxide.
- 24. Questions How can we quantify metabolism? How does the energy source affect the volume of O 2 consumed and volume of CO 2 produced? How do they differ among animals and how are they affected by environmental conditions?
- 25. THE RESPIRATORY QUOTIENT One ratio that is particularly useful for understanding animal metabolism is the respiratory quotient. The respiratory quotient (RQ) measures the ratio of the volume of carbon dioxide (V c ) produced by an organism to the volume of oxygen consumed (V o ).
- 26. RQ = V c /Vo This quotient is useful because the volumes of CO 2 and O 2 produced depends on which fuel source is being metabolized. Measuring RQ is a convenient way to gain information about the source of energy an animal is using. We can then compare the metabolism of animals under different environmental conditions by simply comparing RQ.
- 27. RQ Carbohydrates, such as glucose, are an important source of fuel. The general formula for a carbohydrate is C n H 2n O n . For example, if we take n = 6 we have the formula for glucose, C 6 H 12 O 6 . We can describe the metabolic reaction of a carbohydrate by the following equation: C n H 2n O n + nO 2 --> nCO 2 + nH 2 O
- 28. RQ n=6 C n H 2n O n + nO 2 --> nCO 2 + nH 2 O C 6 H 12 O 6 + 6O 2 --> 6CO 2 + 6H 2 O Now compare the number of molecules of O 2 to the molecules of CO 2 . We have a ratio of 1 to 1, since there are 6 O 2 and 6 CO 2 molecules. RQ = Vc/Vo = 6/6 = 1
- 29. RQ In humans, the use of fats as a fuel source is quantitatively more important than glucose. The general formula for a saturated fat is (CH 2 O) 3 (CH 2 ) 3 n(CO 2 H) 3 . For example, if we take n = 17 we have the formula for the fat glycerol tristearate. C 3n+6 H 6n+9 O 9 + (4.5n + 3.75)O 2 --> (3n + 6)CO 2 + (3n + 4.5)H 2 O
- 30. RQ C 57 H 111 O 9 + 80.25 O 2 57 CO 2 + 55.5 H 2 O RQ = Vc/Vo = 57/80.25 = 0.7 the metabolism of fat consumes a great deal more oxygen RQ for proteins = 0.9
- 31. RQ The respiratory quotient for some animals can change depending on their activity. At rest, a Desert Locust has an RQ of about 1.0. During flight, however, the RQ decreases to about 0.7. How would you interpret this?
Editor's Notes
- #11: 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.
- #12: 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 + O 2 is 2 oxygen atoms both looking for electrons
- #13: Electrons move from molecule to molecule until they combine with O & H ions to form H 2 O It’s like pumping water behind a dam -- if released, it can do work
- #15: 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.
- #19: Where did the glucose come from? from food eaten Where did the O 2 come from? breathed in Where did the CO 2 come from? oxidized carbons cleaved off of the sugars (Krebs Cycle) Where did the CO 2 go? exhaled Where did the H 2 O come from? from O 2 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!
- #20: What if you have a chemical that punches holes in the inner mitochondrial membrane?