:CELLULAR RESPIRATION CH.9 : :cellular respiration= an atp-producing catabolic process in which the ultimate electron acceptor is an inorganic molecule, such as oxygen :*most prevalent and efficient catabolic pathway :*is exergonic process („g=ª686 kcal/mol) :*summarized as: : organic compounds + oxygen --> carbon dioxide + water + energy : :I. ATP and cellular work : a.adenosine triphosphate - made of adenosine and three phosphate groups : i.the cell taps energy in atp by transferring a phosphate group to other compounds : why can't atp just be hydrolyzed? (would release energy as heat which can't be used for work) : *the compound receiving the phosphate group is said to be phosphorylated : *the phosphorylated compound loses its phosphate group as cellular work is performed : *cells must replenish the atp supply to continue their work : :II. respiration is an oxidation-reduction process (chemical reactions which involve a partial or complete tranfer of electrons from one reactant to another; called redox reactions) :a. reductin-gaining electrons or losing oxygen :b. oxidation-losing electrons, hydrogen or the gaining of oxygen. an electron loses potential energy when it shifts from a less electronegative one. a redox reactin that relocates electrons closer to oxygen releases chemical energy which can be put to work. :** in the combustion of glucose, sugar is oxidized and oxygen is reduced. meanwhile, electrons lose potential energy along the way. the released energy is used by cells to make atp. :c. change in covalent bond status :organic molecules with abundance of hydrogen = excellent fuel because their bonds are a source of electrons with high potential energy. they also have the potential to drop the energy when thy move closer to oxygen. the change in covalent status of electrons as hydrogen is transferred to oxygen liberates the energy. :at key steps in aerobic respiration, hydrogen atoms are stripped from the glucose, but not directly transferred tooxygen. they are passed to a coenzyme called nad+ (nicotinamide adenine dinuleotide) which funtions as the ixidizing agent. during this controlled approach to oxygen by hydrogen, a portion of total energy is released and stoed in molecules of atp. : :what is a coenzyme. a small nonprotein organic molecule required for certain enzymes to function. nad+ is an oxidized coenzyme (net+charge); nadh is reduced coenzyme(neutral) : :enzymes called dehyrogenases remove a pari of h atoms from the substrate (2 electrons and 2 protons). these enzymes deliver 2 electrons along with one proton to nad+, forming nadh. the other proton is released as a hydrogen in into the surrounding solution. : :electrons lose very little potential enrgy when they are transferred from glucose to nad+. thus, each nadh molecule formed during respiration represents stored energy that can be used to make atp when the electrons complete thei journey from nadh to oxygen. : :these high energy electrons transferred from substrate (glucose)to nad+ are then passed down the electron transport chain to oxygen, whi»h powers atp synthesis (oxidative phosphorylation). :mitochondria has two membranes; outer is smooth, folds inwards. inner folds are called cristae. surrounding the cristae is the matrix which contains enzymes, co-enzymes, water, phosphates, and moleculees needed in respiration. :outer membrane is permeable to most small molecules, but the inner one permits passage of only certain molecules such as pyruvic acid and atp. :proteins are built into membrane of thecristae (80% protein and 20% lipids); these proteins are involved with the electron transport chain (etc), generating 95% of the atp produced by the mitochondrion. :the etc converts chemical energy from food to a form that can be used to make atp. these transport chains: : *are composed of electron-carrier molecules (the proteins) built into the inner mitochondrial membrane :*accept energy-rich electrons from reduced coenzymes (nadh and fadh2) during a series of redox reactions pass these elecytrons down the chain to oxygen, the final electron acceptor. the oxygen accepts these electrons) along with hydrogen nuclei, to form water :*release energy in a »controlled fashin, which can be harnessed by the cell to power atp production. since the electrons lose potential energy when they shift toward oxygen, it is exergonic. :*each successive carrier in the chain has a higher electronegativity than the carrier before, so the electrons ae pulled downhill towards oxygen : : :OVERVIEW : :these metabolic stages of cellular respiration: :1. glycolysis :2. krebs cycle :3. electron transport chain (etc) and oxidative phosphorylatin : :glycolysis :*occurs in cytosol :*partially oxidizes glucose (6c) into two pyruvate (3c) molecules : :krebs cycle :*occurs in mitochondrial matrix :*completes glucose oxidation by breakin down a pyruvate derivative (acetyl coa) into carbon dioxide : :glycolysis and krebs cycle produce: :*small amount of atp by substrate phosphorylation :*nadh by transferring electrons from substrate to nad+ : :electron transport chain :*located at inner membrane of mitoch. :*accepts high energy electrons from reduced coenzymes (nadh and fadh2) :*couples this exergonic "slide" of electrons to atp synthesis or ixidative phosphorylation. this produces most ofthe atp (90%) : :substrate-level phosphorylation: atp production by enzymatic transfer of phosphate from substrate to adp :oxidative phosphorylation: atp production that is coupled to the exergonic transfer of electrons from food to oxygen :all steps are enzyme meditated