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Chapter 6 Energy Generation in Mitochondria and Chloroplasts (1) Mitochondria: in all eukaryotic cells The relationship between the structure and function of mit. (2) Chloroplasts: in plant cells The relationship between the structure and function of chl. Mit: Oxidative phosphorylation→ ATP Chl: Photosynthesis→ ATP+NADPH→ Sugar 1. Mitochondria and oxidative phosphorylation A. Mitochondrial structure and function The size and number of mitochondria reflect the energy requirements of the cell. Inner and outer mitochondrial membranes enclose two spaces: the matrix and intermembrane space. Outer membrane: Contains channel-forming protein, called Porin. Permeable to all molecules of 5000 daltons or less. Inner membrane (Impermeability): Contains proteins with three types of functions: (1) Electron-transport chain: Carry out oxidation reactions; (2) ATP synthase: Makes ATP in the matrix; (3) Transport proteins: Allow the passage of metabolites Intermembrane space: Contains several enzymes use ATP to phosphorylate other nucleotides. Matrix: Enzymes; Mit DNA, Ribosomes, etc. B. Specific functions localized within the Mit by disruption of the organelle and fractionation Localization of metabolic functions within the mitochondrion Outer membrane: Phospholipid synthesis fatty acid desaturation Fatty acid elongation Inner membrane: Electron transport Oxidative phosphorylation Metabolite transport Marker:monoamine oxidase Cardiolipin/TPL(20%) Marker:cytochrome oxidase Matrix: Pyruvate oxidation Intermembrane space TCA cycle Nucleotide phosphorylation ß oxidation of fats Marker: adenylate kinase DNA replication, RNA transcription, Protein translation Marker: MDH 2. Molecular basis of oxidative phosphorylation A. Molecular basis of oxidation: Electrontransport chain B. Molecular basis of phosphorylation: ATP synthase The structure of the ATP synthase F1 particle is the catalytic subunit; The F0 particle attaches to F1 and is embedded in the inner membrane. F1: 5 subunits in the ratio 3α:3β:1γ:1δ:1ε F0: 1a:2b:12c F1 particles have ATP synthase activity Proton translocation through F0 drives ATP synthesis by F1: Binding Change Model and rotational catalysis Boyer proposed in 1979, and was greatly stimulated by the publication in 1994 of the structure for F1 complex (X-ray) from bovine heart mitochondria Direct experimental evidence supporting the rotational catalysis. Japan researcher, Nature 386: 300, 1997. The ATP synthase is a reversible coupling device Other roles for the proton-motive force in addition to ATP synthase Regulate for Ca2+ C. Mithchell’s Chemiosmotic theory (1961) The pH and electrical gradient resulting from transport of protons links oxidation to phosphorylation. When electrons are passed to carriers only able to accept electrons, the H+ is translocated across the inner membrane. More than 2¯1026 molecules (>160kg) of ATP per day in our bodies. Electrons pass from NADH or FADH2 to O2, the terminal electron acceptor, through a chain of carriers in the inner membrane (FMN, Fe-S center, Heme group Fe, CoQ); As electrons move through the electron-transport chain, H+ are pumped out across the inner membrane, and form Proton motive force; Electrons move through the inner membrane via a series of carriers of decreasing redox potential A testable prediction followed from Mitchell’s hypothesis If not all the detergent is removed, what will happen? Summary of the major activities during aerobic respiration in a mitochondrion NADHO2: 3ATP/2e; FADH2 O2 : 2ATP/2e Ø生物氧化产生ATP的统计: 一个葡萄糖分子经过细胞呼吸全过程产生多少ATP? 糖酵解:底物水平磷酸化产生 4 ATP(细胞质) 己糖分子活化消耗 2 ATP(细胞质) 产生 2NADH,经电子传递产生 3或 5 ATP (线粒体)净积累 5 或 7 ATP 丙酮酸氧化脱羧:产生 2NADH(线粒体),生成 5 ATP 三羧酸循环:底物水平的磷酸化产生(线粒体)2 ATP; 产生 6NADH(线粒体),生成 15 ATP; 产生 2FADH2(线粒体),生成 3 ATP。 总计生成 30 或 32 ATP 3. Chloroplast and photosynthesis A. The structure of Chloroplasts B. Photosynthesis C. The antenna complex and photochemical reaction center in a photosystem Light-dependent reaction: Electron transport in the thylakoid membrane and noncyclic photophosphorylation: Cyclic photophosphorylation: Changes in redox potential during photosynthesis. Carbon dioxide fixation and the synthesis of carbohydrate in C3 plants (Calvin cycle) The structure and function in C4 plants CAM plants: CO2被2次固定,但只 需1种细胞(Mesophyll cell) crassulacean acid metabolism景天植物酸代谢 4. Organelle DNA and protein importing A. Organelle DNA The size range of organelle DNA is similar to that of viral DNAs. ¾Mit DNA: from <6000bp (plasmodium falciparum) ~ >300000bp (some land plants). DNA of Mit genome(in mammals) ≈16500bp(<0.001% of nuclear genome) ; Chl genomes are about 10 times larger and contain about 120 genes. ¾Chl DNA: from 70000 to 200000bp (genome of land plants); Genes in mtDNA encode rRNAs, tRNAs, and some mitochondrial proteins。 Human mt DNA: 16,569bp 2 rRNAs(16s and 12s RNA), 22 tRNAs, 13 polypeptides: NADH reductase. 7 sub. Cty b-c1 complex. 1 cytb Cyt oxidase. 3 subunits ATP synthase: 2 F0 sub The organization of the liverwort(地钱) Chl genome B. Mit and Chl have their own genetic systems Mit and Chl are organelles semiautocephaly. The synthesis of mt proteins is coordinated C. The transport protein into Mit. And Chl. Tree proteins translocators in Mit membranes: ¾TOM, TIM,and OXA complex are multimeric membrane protein, that catalyze protein transport across Mit membrane, TOM, TIM stand for translocase of the outer and inner Mit membranes respectively. ¾TOM functions across the outer membrane; TIM(TIM23 and TIM22) function across the inner membrane. ¾OXA mediates the insertion of inner membrane proteins that are synthesized within the Mit. OXA also helps TOM and TIM to insert some proteins into the matrix. Translocation of precursors to the matrix occurs at the sites where the outer and inner membranes are close together; The protein import by Mit: N-terminal signal sequence is recognized by receptors of TOM; The protein is translocated across both Mit membranes at or near special contact sites. Only unfolded proteins can be imported into Mit; ¾Mit precursor proteins remain unfolded through interactions with hsp70 chaperone proteins in the cytosol after they are synthesized. ATP hydrolysis and H+ gradient are used to dtive protein import into Mit Protein transport into the inner Mit membrane and the intermembrane space requires two signal sequences Two signal sequences are required to direct proteins to the Thylakoid membrane in Chl. Translocation into thylakoid space or thylakoid M can occur by any one of at least four routes. 5. The proliferation and origin of Mit and Chl. A. Organelle growth and division determine the number of Mitochondria and Plastids in a cell Mit fission and fusion (a dividing Mit in a liver cell); Dividing or Budding of Mit. Chloroplasts: dividing and formation of chloroplasts from proplastids begins by the light-induced budding of the inner membrane. B. Origin: The endosymbiont theory Compare the ribosomal RNA with the base sequence of various bacterial rRNAs: Purple bactria-Mitochondria Cyanobacteria-Chloroplasts Suggested evolutionary pathway for the origin of Mit.