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Transcript
Cellular Respiration 2 5/26/11 Electron Transport Chain • • • Takes place in the cristae of mitochondrium – Electron acceptors are embedded in the inner membrane of the cristae Begins with electron from NADH – – Reduces flavoprotein Electron is passed to other molecules that have higher electronegativity • Reduces new acceptor Electron ultimately is accepted by O2 molecule – – Very high electronegativity For every 2 NADH molecules O2 is reduce to 2H2O Electron Transport 2 • • • Each new acceptor requires that the electron be at a slightly lower energy state • All are proteins except Q (ubiquinone) is lipid Energy is siphoned off of the electrons in small increments The energy is used by the acceptor molecules to change conformation •Change in conformation is often linked to pumping H+ across inner membrane Close-up of Cristae • Many electron acceptors used released energy to pump an H+ proton into the intermembrane space – Gradient of H+ is formed outside of cristaes • ATP is actually synthesized by enzyme ATP synthase – Many copies embedded in cristae • Hydrogen gradient needs to reach equilibrium – H+ can only pass through ATP synthase molecule • • Passage of H+ turns molecule like a water wheel Oxidative phosphorylation ATP is generated by enzyme action Net ATP Production • • Glycolysis 2 ATP, Krebs 2 ATP, Electron Transport & oxidative phosphorylation 34 ATP Total of 38 ATP/glucose Photosynthesis and Respiration Complementary processes Plants perform both, heterotrophs only use respiration Each uses waste product of other process (O2 and CO2) Fermentation • • • Used when oxygen is not available as electron acceptor Not as efficient as oxidative phosph. – In humans, only 2 ATP are produced by fermentation Accumulation of waste molecules – Sometimes can be used later as energy source • Type of fermentation is known by waste product Types of Fermentation • Alcohol fermentation – Results in ethanol production – Performed by bacteria and fungi • Lactic acid fermentation – Used by animals – Results in lactate formation – Causes muscles to ache after workout – Anaerobic conditions Why Fermentation • • • Pyruvate is dividing point of two systems If O2 is available pyruvate enters mitochondrium If O2 level is low Pyruvate stays in cytosol and undergoes fermentation • Macromolecules and Respiration Many types of macromolecules can be used as a source for respiration – Fats and proteins are important • They enter pathway at various point Regulation of Respiration • • • Very complex regulation Feedback inhibition of ATP or Citrate can stop early stages of reactions Allows cell to produce ATP when needed