微生物学史微生物学史 (27).ppt

Redox and ETCAfter learning this section,you should be able to:Describe a redox reaction,noting the role of the two half reactionsand identifying the electron donor,electron acceptor,and conjugate redox pairs of the reaction.Redox Reactions:Reactions of Central Importance in MetabolismThe release of energy from an energy source normally involves oxidation-reduction reactions.Oxidation-reduction(redox)reactions are those in which electrons move from an electron donor to an electron acceptor.As electrons move from the donor to acceptor,the donor becomes less energy rich and the acceptor becomes more energy rich.The more electrons a molecule has and is able to donate in a redox reaction,the more energy rich the molecule is.Glucose!It can donate up to 24 electrons in redox reactions,so it is such a excellent source of energy.The acceptor and donor of a half reaction are referred to as a conjugate redox pair.Each redox reaction consists of two half reactions.Oxidation reactionReduction reactionElectron acceptor nicotinamide adenine dinucleotide(NAD+).The NAD+/NADH conjugate redox pair has a very negative E0,and NADH can therefore give electrons to many acceptors,including O2.The equilibrium constant for a redox half reaction is called the standard reduction potential(E0)and is a measure of the tendency of the donor of a half reaction to lose electrons.Conjugate redox pairsElectron Transport Chains:Sets of Sequential Redox ReactionsGlucose NAD+NADH O2CatabolismeeH2OEMPED TAC cycleETCLocation of the ETC The first electron carrier in an ETC has the most negative E0,each successive carrier is slightly less negative.Thus electrons are transferred spontaneously from one carrier to the next.The carriers direct the electrons to the terminal electron acceptor(in this case,O2).Figure 11.11 Creation of a Proton Gradient by the Mitochondrial Electron Transport Chain and Its Use in Synthesis of ATP.Electron carriers in the mitochondrial ETC are organized into four complexes.As electrons move along the ETC,protons are transported across the membrane creating a proton gradient.Proton release occurs when electrons are transferred from carriers,such as FMN and coenzyme Q(Q),that carry both electrons and protons to components such as non heme iron proteins(FeS)and cytochromes(Cyt)that transport only electrons.Complex IV pumps protons across the membrane as electrons pass from cytochrome a to oxygen.The number of protons moved across the membrane at each site per pair of electrons transported is still somewhat uncertain;the current consensus is that at least 10 protons must move outward during NADH oxidation.One molecule of ATP is synthesized and released from the enzyme ATP synthase for every three protons that cross the membrane by passing through it.Wordlist1.oxidation-reduction reactions，redox reaction:氧化还原反应 2.electron 电子3.electron donor电子供体4.electron acceptor电子受体5.conjugate redox pair：共轭氧化还原对6.nicotinamide adenine dinucleotide(NAD+)烟酰胺腺苷酸二核苷酸，还原型辅酶I7.Eo-standard reduction potential 标准氧化还原电势（电位）8.Electron Transport Chains（ETC）电子传递链，呼吸链 Respiration chain9.terminal electron acceptor 最终电子受体10.ATP synthase ATP合酶11.Proton质子