9.23.96 Dr. Pehrson Oxidative phosporylation Handoout: Oxidative Phosphorylation Fall 1996 how a cell converts the energy released by converting food into energy into a useful form. Handout - diagram of ATP. The acid anhydride bonds in ATP and ADP and AMP are high energy bonds - about -3.7 kcal/mol. ATP + GDP <========> ADP + GTP Most of the energy made/utilized is ATP form. ATP + GDP <========> ADP + GTP A <======> B delta G = 4 KCAL/mol Keq= [B]/[A] = 1.15 x 10 -3 So you need a LOT of A (1000 molecules) to get one molecule of B. So, the hydrolysis of ATP can be coupled to this otherwise not that favorable reaction. A + ATP + H2O <==========> B + ADP + Pi + H+ you add the delta G's, and since the ATP + H2O ---> ADP + Pi + H+ rxn has delta G = -7.3, the coupled rxn ends up with delta G = -3.3, so it becomes a favorable reaction. So, as A is converted to B, ATP is being hydrolyzed to ADP. Note that this makes the B--->A reaction very unfavorable now. See front page of handout for math on how this affects the equilibrium constant Keq of the reaction. But, the Keq has become a much larger number than it was before. With the reaction bet A and B coupled to the ATP reaction, you get 100 million times more B out of it. So, the cell, which does many seemingly energetically unfavorable reactions, takes the energy from the ingested material, converts it to ATP, and uses it to drive these unfavorable rxns. committing step of fatty acid biosynthesis: Acetyl CoA + ATP + HCO3- -----> malonyl CoA +ADP + Pi + H+ p.2 of handout---> energy change diagram. if it went to one, that would mean that you had ALL ATP and no ADP or AMP. The cell usually maintains energy at about .8 or .9 on the energy charge axis. catabolic metabolism: fats, polysaccharids and proteins break down into fatty acids, glucose, and AAs, then go to Acetyl CoA and enter the citric acid cycle, giving off CO2 and undergoing oxidative phosphorylation to release O2 and convert ADP TO ATP. If you burn sugar with a torch, you still end up with CO2 and H2O. But the body does it a little differently, conserving the energy which would feed the fire :) FLAME OF LIFE DEMO candle burning on table. as candle burns, wax is liquefied by heat of flame, wax is drawn up the wick and vaporized and burned, releasing a lot of heat. important component not only fuel source, but also AIR. If you deprive candle or person or animal of Air, the flame of life will go out. If you resupply O2 rapidly enough, the flame of life can be restored. biological organisms are VERY dependent on the continuous supply of molecular oxygen. *** what is oxidative phosphorylation? The generation of ATP by the transfer of electrons to O2. Also referred to as respiration on a cellular level. **** 32 of the 36 ATPs produced by oxidation of Glucose are produced by oxidative phosphorylation. Oxidative phosphorylation occurs in the MITOCHONDRIA (p.3 handout) The outer membrane of the mitochondrion is very permeable. The inner membrane where oxidative phosphorylation occurs is very impermeable. the citric acid cycle, TCA, oxidation of fatty acids all occur in the matrix of the mitochondrion. OP has two distinct processes which are normally tightly coupled. 1. ELECTRON TRANSPORT CHAIN -compound is oxidized if it loses electrons and reduced if it gains electrons oxidation and reduction by their very nature are coupled to one another, obviously. oxidant: substance which promotes oxidation of another substance (by recieving electrons) reductant: substance with donates electrons to another substance, promoting reduction of that other substance. eg, Fe3+ + 1e- <====> Fe2+ consider the oxidation states of carbon. H3C-CH3 ethane, gas molecule. can be oxidized to ethanol: H3C-CH2OH <=======> H2C==CH2 (in the presence of H2O then you can get acetaldehyde: H3C-C==O \ OH then acetic acid: H3C-C==O \ OH and then to CO2, ultimately. Malate -----> oxaloacetate in citric acid cycle, NAD takes two H from Malate, goes from NAD to NADH + H+, and forming oxaloacetate as the product. the electrons are conserved per diagram in handout. so, note that every time there is an oxidation, you produce a reduced product as well. Energetics of reduction of O2 by NADH: Flow of electrons to O2 is very favorable, producing 52 kcal/mol. The production of ATP from ADP takes 7.3 kcal/mol. Flow of electron from NADH to O2 occurs through three large protein complexes and two intermediate carriers. See diagram p4 of handout. Why do you need these proteins for the e- to flow in a direction that is already energetically favored? you need a mechanism to store the energy (in the bonds), otherwise it would just dissipate as heat. If you take NADH and dissolve it in H2O, it's fairly stable, because NADH will not give up its electrons spontaneously at room temp without these proteins to catalyze the reaction. also, these proteins can also be regulatory, controlling the rate of reaction. There are also some unpleasant intermediates produced and the proteins help to contain them. So, the electrons are being carried through the chain of proteins and intermediates through a series of oxidation reduction reactions. The proteins involved in this process have developed special groups - prosthetic groups. PROSTHETIC GROUPS - non-proteinaceous group covalently bound to protein, required for biological activity to take place. 4 types: flavin mononucleotide (FMN)--can go to Reduced flavin mononucleotide (FMNH2) iron sulfur complexes- iron can change from 2+ to 3+ cytochromes (heme containing groups) Copper ions - can go from 1+ to 2+ There is also a non-prosthetic group - a separate, unbound molecule, called Ubiquinone, or enzyme Q, with a 50 carbon chain, which lives in the mitochondria, and can accpet one or two electrons. 2. ATP SYNTHESIS