Presentation on theme: "11 Bioenergetics and Metabolism"— Presentation transcript:
111 Bioenergetics and Metabolism Chapter Outline:MitochondriaOxidative PhosphorylationChloroplasts and Other PlastidsPhotosynthesisPeroxisomesamyloplast
2Mitochondria, chloroplasts, peroxisomes Student learning outcomes:Explain similarities, differences structure and function of mitochondria, chloroplast, peroxisomeExplain process of transport of proteins to organelles:signals on proteins, complexes that assistExplain metabolic functions of mitochondria, chloroplast: membrane compartments, proton gradient and ATPMitochondria and chloroplasts have genomes
3Figure 10.3** Overview of protein sorting Cell5e-Fig jpgFig. 10.3
4Generation of metabolic energy- major cell activity IntroductionGeneration of metabolic energy- major cell activityMitochondria generate energy from breakdown of lipids and carbohydrates.Chloroplasts use sunlight energy to generate ATP and the reducing power needed to synthesize carbohydrates from CO2 and H2O.Peroxisomes contain metabolic enzymes:fatty acid oxidation, generate peroxides, have catalase
5Mitochondria are surrounded by double membrane: Outer membrane permeable to small moleculesInner membrane has numerous folds (cristae);extend into interior (matrix).Fig. 11.1
6Fig 11.2 Metabolism in the matrix of mitochondria Matrix contains small genome (human 17 kb; yeast 80 kb)Enzymes for oxidative metabolism:Pyruvate (from glycolysis) into mitochondria; complete oxidation to CO2 yields most of energy (ATP) from glucoseEnzymes of citric acid (Krebs) cycle - in mitochondrial matrix.Most of energy produced by oxidative phosphorylation,occurs on inner mitochondrial membrane(electron transport chain)Fig. 11.2Cell5e-Fig jpg
7MitochondriaHigh-energy electrons from NADH and FADH2 transferred through a membrane carriers membrane to molecular oxygenEnergy of electrons converted to potential energy stored in a proton gradient, which drives ATP synthesis.Inner membrane has many proteins involved in oxidative metabolism and transportInner membrane impermeable to most ions, small molecules
8Outer mitochondrial membrane highly permeable to small molecules: Porins form channels for free diffusion of small molecules.Composition of intermembrane space similar to cytosol(with pH ~7; matrix pH ~8)Mitochondria can fuse,also can divide
9Genomes reflect endosymbiotic origin: Mitochondria have DNAGenomes reflect endosymbiotic origin:usually circular DNA molecules, multiple copies.encode only a few proteins (some oxidative phosphorylation).encode rRNAs and most tRNAs neededfor translating protein-coding sequencesRibosomes are in matrixSome different codon usageTable11.1Human mtDNA16-kbFig. 11.3
10Mutations in mitochondrial genes cause disease Molecular Medicine Diseases of Mitochondria: Leber’s Hereditary Optic Neuropathy: LHON mutations in mitochondrial DNAMutations in mitochondrial genes cause diseaseLeber’s hereditary optic neuropathy, blindness;mutations in mitochondrial genes:components ofelectron transport chainCell5e-MM jpg
11Genes for many mitochondrial proteins in nucleus. Some genes transferred from prokaryotic ancestorMost proteins are synthesized on free cytosolic ribosomes, imported to mitochondria as complete polypeptides.Because of double-membrane structure of mitochondria, import of proteins is complexMatrix proteins are targeted by NH2-terminal sequences (presequences); removed after import
12Figure 11.4 Import of mitochondrial matrix proteins Membrane or free proteinsPresequences targetTom receptors/ channels on outer membrane (translocase)Tim receptors on inner membraneElectrochemical gradientHsp70 ChaperonesMPP cleavageATP hydrolysisCompare ER/GolgiCell5e-Fig jpgFig. 11.4
13Figure 11.5 Binding cycle of an Hsp70 chaperone Presequence cleaved by matrix processing peptidase (MPP)Hsp70 chaperonesfacilitate folding.Similarity to signalpeptidase for ERCell5e-Fig jpgFig. 11.5
14Inner membrane proteins are small molecule transporters. Figure Import of small molecule transport proteins into the mitochondrial inner membraneInner membrane proteins are small molecule transporters.multiple internal import signals,Hsp90 chaperone , plusTom70, translocates across channel.Intermembrane: proteins escorted by mobile Tim22, “Tiny Tims”.Translocated through Tim22; internal stop-transfer signals causes exit insert inner membrane.Cell5e-Fig jpgFig. 11.6
15Both presequences, internal signal sequences. Figure Sorting of proteins containing presequences to different mitochondrial compartmentsBoth presequences, internal signal sequences.Translocated in Tom40.Some exit channel laterally,Some remain in intermembrane spaceOthers transported back to intermembrane spaceOr inserted into inner membraneCell5e-Fig jpgFig. 11.7
16Outer membrane proteins: Figure Insertion of β-barrel proteins into the mitochondrial outer membraneOuter membrane proteins:including Tom40 and β-barrel proteins (e.g., porins),Pass through Tom complex into intermembrane space.Carried by Tiny Tims to a SAM (sorting and assembly machinery) complexInserted into outer membraneCell5e-Fig jpgFig. 11.8
17Phospholipids are imported from cytosol. MitochondriaPhospholipids are imported from cytosol.Phospholipid transfer proteins:take phospholipids from ER membrane,transport them through cytosol,released at new membrane (e.g. mitochondria)Mitochondria catalyzesynthesis of cardiolipinPhospholipid withfour fatty acid chains..
18Figure 10.3** Overview of protein sorting Cell5e-Fig jpg
19The Mechanism of Oxidative Phosphorylation Electrons from NADH and FADH2 combine with O2:Energy released from oxidation/reduction reactionsdrives ATP synthesisElectrons travel through electron transport chainProteins on inner mitochondrial membraneSets up proton gradient across membraneIntermembrane space has lower pH (more H+)Chemiosmotic mechanism for synthesis of ATP:Protons returning to matrix power ATP synthase.
20Fig 11.10 Transport of electrons from NADH Transfer of electrons from NADH:Complex I,Coenzyme Q (ubiquinone)Complex IIICytochrome cComplex IV(cytochrome oxidase)to O23 H+ transportedacross membraneV is ATP synthase:H+ reentry gives ATPCell5e-Fig R.jpgFig
21Fig 11.11 Transport of electrons from FADH2 Transfer of electrons from FADH2:Complex II (less energy)Coenzyme Q (ubiquinone)Complex IIICytochrome cComplex IV(cytochrome oxidase)to O23 H+ transportedacross membraneV is ATP synthase:H+ reentry gives ATPCell5e-Fig jpgFig
22The Mechanism of Oxidative Phosphorylation Chemiosmotic coupling mechanism:Couples electron transport to ATP generation.Electron transport coupled to transport of protons to intermembrane spaceProton gradientacross inner membraneAlso electric potentialElectrochemicalgradient existsFig
23Fig 11.13 Structure of ATP synthase Phospholipid bilayer impermeable to ionsProtons cross through protein channel.Energy converted to ATPin complex V (ATP synthase):F0 is channelF1 rotates, makes ATP4 protons to synthesize 1 ATP:1 NADH yields 3 ATP;1 FADH2 yields 2 ATPCell5e-Fig jpgFig
24Fig 11.14 Transport of metabolites across the mitochondrial inner membrane Electrochemical gradient drives transport of small molecules into and out of mitochondria.ATP exported; ADP and Pi brought in.Integral membrane protein transports 1 ADP in, 1 ATP outPyruvate exchanged for OH-Cell5e-Fig jpgFig
25Chloroplasts and Other Plastids Chloroplasts: organelles for photosynthesis:Convert CO2 plus H2O to carbohydratesSynthesize amino acids, fatty acids, and lipids of their membranes.Similar to mitochondria:generate metabolic energy,evolved by endosymbiosis,contain own genomereplicate by division.
26Figure 11.15 Structure of a chloroplast Chloroplasts are larger and more complex:double membrane — chloroplast envelope.internal membrane system, thylakoid membrane,network of flattened discs (thylakoids),arranged in stacks (grana)3 internal compartments:intermembrane spacestroma, ~ mitochondrial matrixthylakoid lumenElectron transport, chemiosmoticgeneration of ATP in thylakoid membrane,not in intermembrane spaceCell5e-Fig jpgFig
27**Comparison chemiosmotic mechanism locations Fig Chemiosmotic generation of ATP in chloroplasts and mitochondria**Comparison chemiosmotic mechanism locationsCell5e-Fig jpgFig
28Chloroplasts and Other Plastids Chloroplast genome reflects evolutionary origins from photosynthetic bacteria.Circular DNA molecules, multiple copies,Encode RNAs, proteins for gene expression, photosynthesisRubisco catalyzes addition of CO2 to ribulose-1,5-bisphosphate during the Calvin cycle. Rubisco is critical enzyme for photosynthesis,
29Chloroplasts and Other Plastids Proteins from cytosolic ribosomes imported after completionN-terminal transit peptideGuidance complexProteolytic cleavageToc complexHsp70 chaperonesTic complexSPP stromal processing peptidaseFig
30Fig 11.18 Import of proteins into the thylakoid lumen or membrane Thylakoid proteins have second signal sequence, (exposed after cleavage of transit peptide).3 paths:Chaperones+ chargeSRP (signalrecognition particle)Cell5e-Fig jpgFig
31Chloroplasts and Other Plastids of Plants Double-membrane organelles including chloroplastsPlastids contain same genome, differ in structure and function.Chloroplasts unique: internal thylakoid membrane and photosynthesisClassified by pigments
32Fig 11.19 Electron micrographs of chromoplasts and amyloplasts Chloroplasts contain chlorophyll.Chromoplasts contain carotenoids: result in yellow, orange, red colors of flowers and fruitsLeucoplasts are nonpigmented - store energy sources in nonphotosynthetic tissues.Amyloplasts store starchElaioplasts store lipidsCell5e-Fig jpg
33Chloroplasts and Other Plastids Plastids develop from proplastids,small undifferentiated organellesMature plastids change.Chromoplasts from chloroplasts,in ripening fruit.Proplastids arrested atintermediate stage (etioplasts).In light, etioplasts developinto chloroplasts.Fig
344. Photosynthesis: ultimate source of energy for biological systems: Light reactions:energy from sunlight drives synthesis of ATP and NADPH, coupled to formation of O2 from H2O.Dark reactions:ATP and NADPH drive glucose synthesisCO2 plus H2O form sugars
35Fig 11.22 Organization of a photocenter Sunlight absorbed by photosynthetic pigments - chlorophylls.Photocenters in thylakoid membrane have pigment moleculesAbsorption of light excites electron, converts light energy to potential chemical energy.Electrons transferred through membrane carrier chain, results in synthesis of ATP and NADPHCell5e-Fig jpgFig
36Fig 11.25 Electron transport and ATP synthesis during photosynthesis Photosynthesis: electron transport chain4 complexes on thylakoid membrane.2 photosystems (photosystems I and II); split H2OCytochrome bf complexNADP reductase forms NADPHH+ gradient in thylakoid lumenATP synthaseCell5e-Fig jpg
37Fig 11.27 The pathway of cyclic electron flow Cyclic electron flow uses electrons from Photosystem I only,generates extra ATP but not NADPHFigCell5e-Fig jpg
38Summary photosynthesis: Thylakoid membrane impermeable to protons, is permeable to other ions, particularly Mg2+ and Cl–Difference more than 3 pH units between stroma and thylakoid lumen → lot of energy across membrane.Each pair of electrons gives 2 protons at photosystem II, 2–4 protons cytochrome bf complex.4 protons for synthesis of 1 ATP: each pair electrons yields 1 to 1.5 ATP.Cyclic electron flow yields 0.5 to 1 ATP per pair electrons.
39PeroxisomesPeroxisomes:Single-membrane-enclosed organelles that contain diverse metabolic enzymes (peroxins)no genomeFig
40PeroxisomesPeroxisomes break down substrates by oxidative reactions, produce hydrogen peroxide.Peroxisomes contain catalase: converts H2O2 to water or uses it to oxidize other organic compound.Peroxisomes synthesize lipids, amino acid lysine.In animal cells, cholesterol and dolichol are synthesized in peroxisomes and in ER.In liver, peroxisomes synthesize bile acids from cholesterolFig
41Peroxisome assembly Peroxisomes Begins on rough ER: 2 peroxins localize.Pex3/Pex19-containing vesicles bud off ERPTS1,2 signals target proteinsfrom free ribosome to join peroxisomeSignals recognized byreceptors and protein channelsProtein import, addition of lipidsresults in peroxisome growth, division.Enzyme content, metabolic activitiesof peroxisomes can changeFig
42lethal within first 10 years of life, PeroxisomesDiseases from deficiencies in peroxisomal enzymes, or failed import into peroxisome.Zellweger syndrome,lethal within first 10 years of life,results from mutations in at least10 different genes affectingperoxisomal protein import.Peroxisome biogenesis disorders (PBD)– part of leukodystrophies.Damage white matter of brain,affect metabolism in blood and tissues.
43Review Questions:What 2 properties of mitochondrial inner membrane give it unusually high metabolic activity?What roles do molecular chaperones play in mitochondrial protein import?Compare/ contrast import of proteins into mitochondria and into chloroplast – membrane vs. cytoplasm11. How are proteins targeted to peroxisomes?