线粒体基因组.pptx

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1、Mitochondrial molecular genetics focusonmitochondria:briefoverviewoftheirfunctionandstructuremtDNAstructureandreplication:-animals-yeast-plantsinheritanceofmitochondria-petitemutantsofyeastbiogenesisofmitochondriabyfission第1页/共78页MITOCHONDRIA essential for cell life-ATP synthesis-many metabolic inte

2、rmediates essential for cell death -unprogrammed death:necrosis(eg,due to loss of energy status)-programmed cell death(apoptosis-controlled cell destruction)第2页/共78页 Two membranes Inner membrane invaginated Numbers of mitochondria per cell vary but usually 100s/cellMatrix contains the TCA cycle(and

3、other)soluble enzymesInner membrane contains metabolite transporters and the electron transport chainMitochondrial structure第3页/共78页Theribosomescanactuallybevisualizedinsomemitochondria.Inthesefigures,theyareseeninthematrixassmalldarkbodies.DNAcanalsobevisualizedinmitochondria.TheDNAiscircularandres

4、emblesthatofabacteriuminitsbasicstructure.MitochondriaalsohavetheirownribosomesandtRNA:22tRNAsrRNAs(16Sand12S)第4页/共78页MitochondriacontainDNAmoleculeswithanassortmentofgenes.MitochondrialgeneticsystemconsistofDNAandthemolecularmachineryneededtoreplicateandexpressthegenescontainedinthisDNA.Thismachine

5、ryincludesthemacromoleculesneededfortranscriptionandtranslation.Mitochondriaevenpossesstheir own ribosomes.Many of these macromolecules are encoded by mitochondrialgenes,butsomeareencodedbynucleargenesandarethereforeimportedfromthecytosol.第5页/共78页MitochondriahavetheirownDNAandRibosomesMitochondriaha

6、vesomeoftheirownDNA,ribosomes,andcanmakemanyoftheirownproteins.TheDNAiscircularandliesinthematrixinstructurescallednucleoids.Eachnucleoidmaycontain4-5copiesofthemitochondrialDNA(mtDNA).mitochondrialDNA第6页/共78页Mitochondrial DNA(mtDNA)mtDNA was discovered in the 1960s;revealed asDNA-like fibers within

7、 mitochondria.The completenucleotidesequencesofmtDNAmoleculesfrommanydifferentspecieshavenowbeendetermined.mtDNA vary enormously in size,from about 6kb inPlasmodium to 2500 kb in some of the floweringplants.EachmitochondrionappearstocontainseveralcopiesofDNA.第7页/共78页Mitochondrial DNA(mtDNA)In a vert

8、ebrate oocyte,for example,it has beenestimated that as many as 100 million copies of themtDNA are present.Somatic cells,however,havefewercopies,perhapslessthan1000.Most mtDNA molecules are circular,but in somespecies,suchasalgaChlamydomonas reinhardtii 莱茵衣藻,theyarelinear.Inthevertebrates37distinctge

9、nesarepackedintoa16 to 17-kb circle leaving little or no space betweengenes.第8页/共78页 MITOCHONDRIAL DNA(YELLOW)IN THE UNICELLULAR ORGANISM EUGLENA GRACILIS.THE NUCLEAR DNA(RED)IS ALSO VISIBLE.第9页/共78页Plant mtDNAIn some of the flowering plants an unknown number of genes are dispersed over a very large

10、 circular DNA molecule hundreds or thousands of kilobase in size.In these plants the mitochondrial genes may become separated onto different circular molecules by a process of intramolecular recombination.第10页/共78页Plant mtDNAThis recombination is mediated by repetitive sequences located in the mtDNA

11、.An exchange between two of the repetitive sequences can partition the“master”mtDNA circle into two smaller circle,a process that superficially resembles the excision of a lambda prophage from E.coli chromosome.In some species,several DNA circles of different sizes are formed by recombination betwee

12、n pairs of repetitive sequences located at different positions around the master DNA circle.These molecules is difficult to study,and more research is needed to elucidate the mechanism that produces them.第11页/共78页Intramolecular recombination in the mtDNA of the Chinese cabbage,Brassica campestris油菜.

13、Recombination between the repeated elements in the large circular DNA molecule partitions this molecule into two smaller ones.Alternatively,the repeated elements in the two small molecules may recombine with each other to produce a single large molecule.第12页/共78页The structure of mtDNAThestructureofm

14、tDNAmoleculeshasbeenstudiedbyDNAsequencing.AnimalmtDNAissmallandcompact.Inhumanbeings,forexample,themtDNA is16,659basepairslongandcontains37genes,includingtwothatencoderibosomalRNAs,22 encode transfer RNAs,and 13 that encodepolypeptidesinvolvedinoxidativephosphorylation,theprocess that mitochondria

15、use to recruit energy.Inmice,cattle,andfrogs,themtDNAissimilartothatofhumanbeingsanindicationofabasicconservationofstructurewithinthevertebratesubphylum.第13页/共78页Map of human mtDNA showing the pattern of transcription.Genes on the inner circle are transcribed from the L strand of the DNA,whereas gen

16、es on the outer circle are transcribed from the H strand of the DNA.Arrows show the direction of transcription.ND1-6 are genes encoding subunits of the enzyme NADH reductase;the tRNA genes in the mtDNA are indicated by abbreviations for the amino acids.第14页/共78页The structure of mtDNAInvertebrate mtD

17、NA is about the same size asvertebrate mtDNA,but it has a somewhat differentgenetic organization.These differences seem to havebeencaused by structuralrearrangementsof thegeneswithincircularmtDNAmolecule.第15页/共78页The structure of mtDNAIn fungi,the mtDNA is considerably larger than it is in animals.Y

18、east,for example,possesses circular mtDNA molecules 78 kb long.These molecules contain at least 33 genes,including 2 that encode ribosomal RNAs,23 to 25 that encode transfer RNAs,1 that encodes a ribosomal protein,and 7 encode different polypeptides involved in oxidative phosphorylation.The yeast mt

19、DNA is larger than animal mtDNA because several of its genes contain introns and there are long noncoding sequences between some of the genes.Animal mtDNA does not contain introns.第16页/共78页The structure of mtDNAPlant mtDNA is much larger than the mtDNA of othersorganisms.It is also more variable in

20、structure.Theseconclusions come from crude physical and chemical analysisandfromDNAsequencing.One of the first plant mtDNAs to be sequenced is from theliverwort地钱,Marchantia polymorpha.ThemtDNAfromthisprimitive,nonvascular(非 维 管)plant is a 186-kb circularmolecule with 94 substantial open reading fra

21、mes(ORFs),some corresponding to known genes and others having stillunassigned genetic functions.The latter ORFs are thereforecalledURFs,forunassignedreadingframes.32distinctintronshave been found in the Marchantia mtDNA,accounting forabout 20%of the molecule.In vascular(维 管)plants,themtDNA islargert

22、hanitisinMarchantia;forexample,itisa570-kb circular molecule in maize and a 300-kb circle in thewatermelon西瓜.第17页/共78页The structure of mtDNAHigher plant mtDNA molecules contain many noncoding sequences,including some that are duplicated.The actual number of genes per mtDNA molecule is unknown.Physic

23、al mapping of some of these genes has shown that they are located in different position in the mtDNA circles of different species,even when the species are fairly closely related.This implies that mtDNA of higher plants has undergone many genetic rearrangements during its evolution.第18页/共78页Expressi

24、on of Mitochondrial genesThe simple mtDNA of vertebrates are organized into two large transcription unit,each encoding the information of several genes.When the two strand of human mtDNA are separated by centrifugation,one proves to be denser the H strand(for heavy),than the other referred as the L(

25、for light).The promoters for the H and L transcription units are situated just upstream of the phenylalanine tRNA gene.The transcripts are extended in opposite directions around the mtDNA molecule.第19页/共78页The transcript from the H strand encodes 2 ribosomal RNAs,14 tRNAs,and 12 polypeptides.The tra

26、nscript from the L strand encodes 8 tRNAs and 1 polypeptide.Each transcript is cleaved to separate the tRNAs from the rRNAs and mRNAs,and mRNAs are polyadenylated.Each mRNA is then translated into polypeptides,using the mitochondrial ribosomes and a combination of nuclear and ribosomal tRNAs.Express

27、ion of Mitochondrial genes第20页/共78页 Translation in the mitochondria proceeds much as it does on the ribosomes of the cytosol,except that some of the codons have a different meaning.AGA and AGG are termination codons in mammalian mitochondria,whereas in the cytosol they specify the incorporation of a

28、rginine;UGA,which is termination codon in the cytosol,is a tryptophan codon in the mitochondria;and AUA,which encodes isoleucine in cytosol,is the methionine initiation codon in the mitochondria.Expression of Mitochondrial genes第21页/共78页In fungi and plants the mtDNA is organized into many separate t

29、ranscription units,some containing the information for more than one gene.Little is known about the details of transcription,but in yeast,the mitochondrial RNA polymerase is a single polypeptide encoded by a nuclear gene.RNA processing separates plant mitochondrial transcripts into their constituent

30、 parts and also removes the introns,which are present in several plant mitochondrial genes.THE MECHANICS OF THESE EVENTS ARE POORLY UNDERSTOOD.Expression of Mitochondrial genes第22页/共78页Another peculiarity of plant mitochondrial gene expression is that many of the mtRNA transcripts undergo editing;th

31、at is,some of the nucleotides are changed after transcript has been synthesized.The most frequent change is C to U(occasionally U to C).Thus,RNA editing alters the composition of codons in plant mitochondrial transcript.Editing alters the information that is actually encoded in the mtDNA and allows

32、functional polypeptides to be synthesized.Editing is not found in the nonvascular plants(mosses and algae藻类和苔藓植物).The editing mechanism probably evolved sometime after plants had become established on the land.Expression of Mitochondrial genes第23页/共78页Yet a third peculiarity of plant mitochondrial g

33、ene expression is that some mitochondrial mRNAs are formed by the process of trans-splicing.It occurs when segments of a gene are scattered over the mtDNA molecule.Each gene segment is transcribed independently,and exons of the different transcripts are spliced together by interactions between the i

34、ntrons that flank them.Expression of Mitochondrial genes分子内(intramolecular)剪接(cis splicing)以及分子间(intermolecular)剪接(trans splicing)第24页/共78页Trans-splicing in wheat mitochondria.Four different RNAs contribute to the final mRNA encoding a polypeptide of the enzyme NDH reductase.第25页/共78页 INTERPLAY BETW

35、EEN MITOCHONDRIAL AND NUCLEAR GENE PRODUCTSMost perhaps all-mitochondrial gene products function solely within mitochondrion.However,they do not function alone.Many nuclear gene products are imported to augment or facilitate their function.Many of the polypeptides needed for aerobic metabolism are a

36、lso synthesized in cytosol(ATPase that is responsible for binding the energy of aerobic metabolism into ATP).However,because some of the subunits of this protein are synthesized in the mitochondria,the complete protein is actually a mixture of nuclear and mitochondrial gene products.第26页/共78页 INTERP

37、LAY BETWEEN MITOCHONDRIAL AND NUCLEAR GENE PRODUCTSThis dual(双重的)composition suggests that nuclear and the mitochondrial genetic systems are coordinated in some way so that equivalent amounts of their products are made;possible molecular mechanisms for this coordination are currently under investiga

38、tion.第27页/共78页KEY POINTSmtDNA molecules range from 6-kb to 2500-kb in size,and most of them appear to be circular.mtDNA molecules contain genes for some of the ribosomal RNAs,transfer RNAs,and polypeptides used within the mitochondrion.The structure,organization,and expression of mitochondrial genes

39、 vary among species.In some organisms,the transcripts of mitochondrial genes are edited after they are synthesized.Both mitochondrial and nuclear gene products are needed for normal mitochondrial function.第28页/共78页mt DNA and human disease Recent research has demonstrated that several human diseases

40、are caused by mitochondrial defects,and in some cases,these defects are due to mutations in the mtDNA.One such disease is Lebers hereditary optic neuropathy(LHON),a condition characterized by the sudden onset of blindness in adults.This disease is associated with the death of the optic nerve(at a ph

41、ysiological level),and with mutation in any of several mitochondrial genes(at a molecular level).Each mutation changes an amino acid in one of the mitochondrial proteins reducing the efficiency of oxidative phosphorylation.The reduction is great enough to destroy the function of the optic nerve and

42、cause total blindness.It is not known why this effect is limited to the optic nerve.LHON is inherited strictly through the maternal line.第29页/共78页Another disorder caused by a mutation in the mtDNA is a Pearson marrow-pancreas syndrome,characterized by a loss of bone-marrow cells during childhood,is

43、frequently fatal.It is caused by a fairly large deletions in the mtDNA.People with this syndrome almost never have affected parents.Thus,the causative deletion probably occurs spontaneously during development in the child or during oogenesis in the mother.Individuals with Pearson syndrome actually h

44、ave a mixture of deleted and normal mtDNA an example of mitochondrial heteroplasmy.Homoplasmic individuals have never been observed.mt DNA and human disease第30页/共78页The molecular genetics ofChloroplastsChloroplasts contain DNA molecules with an assortment of genes.Chloroplast are specialized forms o

45、f a general class of plant organelles called plastids质体质体.Botanists distinguish among several kinds of plastids,including chloroplasts(plastids containing pigments),amyloplasts(plastids containing starch造粉体：一种形成淀粉的植物性白色体),and elaioplasts(油质体 plastids containing oil or lipid).All three types seem to

46、develop from small membrane-bounded organelles called proplastids前 质 体,and,within a particular plant species,all seem to contain the same DNA.This DNA is generally referred to as chloroplast DNA,abbreviated simply as cpDNA.第31页/共78页CHLOROPLAST DNAIn higher plants,cpDNA typically range from 120 to 16

47、0 kb in size,and in algae,from 85 to 292 kb.In a few species of green algae the cpDNA is much larger,about 2000 kb.The cpDNA seems to be organized as a closed circular molecule,but in some species(with large cpDNAs)a linear arrangement cannot be ruled out.The number of cpDNA molecules in a cell depe

48、nds on two factors:the number of chloroplasts and the number of cpDNA molecules within each chloroplast.第32页/共78页CHLOROPLAST DNAAll cpDNA molecules carry basically the same set of genes,but in different species these genes are arranged in different ways.The basic gene set includes genes for ribosoma

49、l RNAs,transfer RNAs,some ribosomal proteins,various polypeptide components of photosystems that are involved in capturing solar energy,four subunits of a ribulose 1,5-biphosphate carboxylase磷酸核酮糖梭化酶,and four subunit of a chloroplast-specific RNA polymerase.Most cpDNAs have a pair of large inverted

50、repeats that contain the genes for ribosomal RNAs.These repeats range anywhere from 10 to 76 kb in length and are variously located in different cpDNA molecules.第33页/共78页.Genetic organization of the chloroplast DNA in the liverwort Marchantia polymorpha.Symbols:rpo,RNA polymerase;rps,ribosomal prote