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Cellular Respiration.docx

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BIOL 130
Heidi Engelhardt

Cellular Respiration  Cellular respiration – what is the overall objective?  Major Players in Cellular Respiration o ATP – reminder of structure  phosphorylation activates proteins and powers reactions o ATP and coupling of exergonic and endergonic reactions  two ways of making ATP o How to resynthesize ATP?  reduction-oxidation reactions  overall equations for photosynthesis, cellular respiration  Electron carriers capture energy from glucose oxidation.  NAD , FADH, NADP +  Stages of Cellular Respiration 1. Glycolysis – priming, cleavage and energy harvesting r(x)s regulation – phosphofructokinase 2. Pyruvate processing  acetyl CoA acetyl CoA and energy metabolism 3. TCA (citric acid/ Krebs) cycle regulatory points 4. Electron transport chain and generation of proton gradient ATP synthase  Overall yield and efficiency of aerobic respiration  ‘Chemiosmotic Theory’ - proton motive force, chemi-osmosis  anaerobic metabolism  oxidizing fuels other than glucose CELLULAR RESPIRATION  Cells require energy o Obtained from chemical bond energy stored in ‘food’ o Most important source is carbohydrate (sugar)  Sugars oxidized to C2 and H2O  Energy stored in high energy bonds of activated carrier molecules (eg. ATP and NADH)  Obtaining energy from food o Breakdown of complex molecules into simpler ones (by enzymes)  catabolism o Opposite process  anabolism  Burning sugar o chemically, little difference between these reactions:  reactants are CHOs and oxygen, products are CO2and water and energy  energy is released by the breaking of six C-H bonds in glucose  total energy release is the same o the difference:  in burning glucose all energy is released as heat  cell can’t use heat, must harvest in tiny, tightly controlled steps such that most energy is captured/stored as ATP  Smaller activation energy (can be overcome by body temperature)  3 ways to make ATP o Substrate level phosphorylation  generates a few ATP during glycolysis (initial breakdown / rearrangement of glucose) o Oxidative Phosphorylation (aerobic respiration) +  electrons harvested from organic fuel molecules in redox reactions used to pump H across a membrane (proton pump)  protons are then allowed to back across (diffusing down their gradient) and run ATP synthase o Photophosphorylation  occurs in chloroplasts  cyclic and non-cyclic phosphorylation  Cellular Respiration o Stages:  Digestion  Outside of cells (intestine) or in lysosome  Digestive enzymes reduce macromolecules into their monomeric subunits o proteinsamino acids o polysaccharides sugars o fats fatty acids and glycerol  Small organic molecules make their way to cytosol o Oxidation process for generation of ATP begins  Glycolysis  Converts each molecule of glucose into 2 pyruvate molecules  Other sugar molecules can enter at different points of the glycolytic pathway  Results in the formation of activated carrier molecules o ATP and NADH  Pyruvate is transported from cytosol into mitochondrial matrix o Transformed into Acetyl-CoA and C2 o Acetyl CoA can also be produced directly from the oxidation of fatty acids  Takes place in cytoplasm  Highlights o 2 ATPs spent to make glucose more reactive o doubly phosphorylated sugar is split o each 3C sugar joins with a free phosphate, making sugar even more reactive o in final steps, 2 phosphate groups on each sugar are transferred to ATP o 2 NAD+ are reduced into 2 NADH  ATP gain o Spend 2 ATP and gain 4 ATP- net gain of 2 ATP o ~24 kcal / mol glucose  Prepping pyruvate  Co-enzyme A o a nucleotide derivative o an organophosphate o a thiol o a coenzyme  thiol group reacts with carboxylic acids  ‘carries‘ acyl group: activated 2 carbon acetyl group derived from pyruvate  Pyruvate dehydrogenase complex o Contains 60 polypeptide chains  decarboxylation reaction: taking off a carbon (released as2CO )  reducing (loading) NAD+ (NADH is formed)  ‘activating’ 2-carbon acyl groups +  pyruvate + NAD + CoA  acetyl-CoA + NADH + CO 2  TCA cycle  Oxidative portion occurs in mitochondria  Acetyl group of acetyl-CoA is transferred to OAA  Forms citrate o Enters a cyclic series of reactions  TCA cycle o Net result is that the transferred acetyl group (from glucose) is oxidize2 to CO o This process generates a large amount of NADH  Acetyl-CoA o Where do the acyl groups come from to form acetyl CoA?  oxidation of pyruvate (a CHO)  breakdown of proteins  breakdown of fats, other lipids o What can the cell do with acetyl CoA?  oxidize it to make ATP (TCA cycle  cellular respiration)  fat synthesis o Which process predominates?  lots of ATP in cell  oxidative pathway inhibited  cell makes fatty acids  stores fat  low ATP in cell  oxidative pathway predominates  2 carbon acetyl unit is fully oxidized to yield: o 2 CO2 o 1 GTP ≅ 1 ATP (substrate-level phosphorylation) o Reduced (activated) electron carriers: 3 NADH, 1 FAD2  molecule required to restart the cycle is regenerated  Oxidative phosphorylation (Electron transport chain)  Occurs in the mitochondria  loaded energy carriers (NADH, FADH 2 carry their electrons to the matrix side of the inner mitochondrial membrane  they transfer electrons to a series of membrane-associated proteins that shuttle electrons in redox reactions  series of proteins embedded in inner mitochondrial membrane o NADH delivers electrons to top of chain, oxygen catches them at the bottom o oxygen then joins with hydrogens to form water  output: o for every two electron carriers, on2 O molecule is reduced to two molecules of water o energy released by movement of electrons in redox reactions used to generate proton gradient across the inner mitochondrial membrane  components: o most of the molecules are proteins with distinct chemical groups that are readily oxidized or reduced  flavins, iron-sulfur complexes, iron-heme groups o molecules are arranged from lower to higher electronegativity  electrons are held tighter and tighter as they pass down chain o ultimate electron acceptor is oxygen  all electrons in original glucose can be accounted for  Chemiosmosis
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