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Lecture 8

Lecture 8- cellular energetics.docx

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Kathleen Gilmour

Lecture 8- Topic 3 (cellular energetics) Slide 14 glycolisis occurs in cytoplasm of the cell which generates it generates pyruvate which then has to enter the mitochondrion for the rest of the pathway to proceed in the presence of oxygen. It enters external layer by porins and intracellular layer by means of proton co transport mechanism. once inside it oxidizes to Acetyl co enzyme A Slide 16 Fist step in pathway is pyruvate oxidation. once it enters mitochondrial matrix it undergoes oxidative decarboxylation. This means 3 carbon pyruvate has a cabon removed, leaving a 2 carbon (acetyl molecule) that is attached to co-enzyme A, the energy released dries reduction of NAD+ to NADH. In context of glucose, each glucose yields 2 pyruvate, and therefore 2 NADH, and to Actyl CoA molecules that enter citric acid cycle. Slide 17 Citric acid cycle regenerates the initial intermediate in the end. 1st-6 carbon molecule called citrate, it is catalyzed by citrate synthase. Once citrate is generated there are two rounds of oxidative decarboxylation, and each of these rounds one carbon is taken off, and converted to inorganic carbon, and each time energy is release creating NADH. this happens twice in succession. at the end of the two steps, all of the carbon given from glucose has become inorganic carbon, and the final step is converting the 4 carbon molecule that is left back into oxaloacetate the intermediate that enters the cycle. this conversion process also yields energy, (one molecule of ATP, FADH, and NADH) In total one turn of the cycle yields: 3 NADH 1 FADH2 1ATP And keep in mind that the cycle goes through twice for every glucose molecule that enters the cycle. Slide 18 End of citric acid cycle we have 2 ATP, & 2 more from glycolisis, 2 NADH from glycolisis, 2 from pyruvate oxidation, and 6 from citric acid cycle, swell as 2 FADH2 from citric acid cycle. Slide 19 oxidative phosphorylation is bassicly looking at ATP that are produced due to a proton gradient. 2 step process, electrons are transferred to oxygen yielding energy to pump protons, and that proton gradient is then used to drive tap synthesis. and this whole thing is what is called oxidative phosphorylation. (chemiosmotic model of ATP synthesis) energy is used to create gradient, and the gradient is used to drive ATP synthesis. Carriers in the process are found on the inner mitochondrial membrane, and they are made up of integral membrane proteins that have prosthetic groups have capture the electrons and pass them along to the next part of the group. (true for complex 1,3,& 4) complex 2 is different because its a single protein rather than a whole bunch, and its a peripheral membrane protein rather than integral. (attached to matrix side) NADH is captured by complex 1, and FADH is captured by complex 2. the electrons from both are then transferred by the use of the transporter ubiquinone. and this is a hydrophobic co-enzyme that is found on the interior of the membrane, and cytochrome c transports electrons from complex 3 to ,and it is also a peripheral membrane protein. on inter membrane space side. And finally complex 4 transfers electrons to oxygen. value of this, is that the energy released by this transfer pumps hydrogens from matrix to inter membrane space. Slide 20 ATP synthase is a large protein complex that is in 2 parts. One embedded into the membrane, and the other in the matrix. Both parts spin. protons move into the part that is embedded and cause it to turn, and that acts a molecular motor causing the bottom portion also to turn and resulting in the production of ATP. you get more ATP from the NADH being fed through because it starts at complex 1, therefore there are more electrons being pumped than FADH which only starts at complex 2. For each NADH you get 3 ATP For each FADH2 you get only 2 ATP b/c of what was said above Throught oxidative phosphorylation you are able to feed 10 NADH into and 2 FADH2 to yield 30ATP/4ATP = total 34 tap, compared to 4 atp gained from glycolisis and citric acid cycle. Most atp come from oxidative. grand total for bacterium is 38 ATP, but for eukaryotic cell the total is ONLY 36 ATP. WHY? do eukaryotic cells net less ATP in total. Answer: Glycolosis occurs in cytoplams of eukaryotic cell, so pyruvate and NADH that are formed need to enter mitochondrion for next steps to continue and this requires energy. The energy is used to move pyryvate and NADH Efficiency of ATP (40~50%) the remainde
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