MtDNA encoding genes of electrontransport chainGenesCategoryNADH dehydrogenaseMT-ND1,MT-ND2,MT-ND3,MT-ND4,MT-(complex I)ND4L.MT-ND5.MT-ND6MT-CYBCoenzymeQ-cytochromecreductase/Cytochromeb(complex III)cytochrome c oxidaseMT-CO1.MT-CO2.MT-CO3(complex IV)ATPsynthaseMT-ATP6,MT-ATP816
16 MtDNA encoding genes of electron transport chain Category Genes NADH dehydrogenase (complex I) MT-ND1, MT-ND2, MT-ND3, MT-ND4, MTND4L, MT-ND5, MT-ND6 Coenzyme Q - cytochrome c reductase/Cytochrome b (complex III) MT-CYB cytochrome c oxidase (complex IV) MT-CO1, MT-CO2, MT-CO3 ATP synthase MT-ATP6, MT-ATP8
The limited autonomy of themitochondrialgenome（线粒体基因组的半自主性）MitochondrialEncoded byEncodedbynuclearMitochondrial genomecomponentgenome13subunitsComponents of80 subunitsoxidativephosphorylationsystem24approx 80Componentsofprotein synthesisapparatus17
17 The limited autonomy of the mitochondrial genome（线粒体基因组的半自主性） Mitochondrial component Encoded by Mitochondrial genome Encoded by nuclear genome Components of oxidative phosphorylation system 13 subunits 80 subunits Components of protein synthesis apparatus 24 approx 80
The human nuclear and mitochondrial genomesNuclearGenomeMitochondrial GenomeSize3200 Mb16.6 kbNo. of different DNA23 (in XX cells) or 24One circularDNAmolecules(in XY cells); all linearmoleculeOftenseveralTotal no.of DNA46in diploid cells, butmoleculespercellvaries according tothousands (but variableploidyAssociated proteinSeveral classes ofLargely free of proteinhistone&nonhistoneprotein37No. of genes~30000~35-0001/0.45 kbGene density~1/100kb18
18 The human nuclear and mitochondrial genomes Nuclear Genome Mitochondrial Genome Size 3200 Mb 16.6 kb No. of different DNA molecules 23 (in XX cells) or 24 (in XY cells); all linear One circular DNA molecule Total no. of DNA molecules per cell 46 in diploid cells, but varies according to ploidy Often several thousands (but variable Associated protein Several classes of histone & nonhistone protein Largely free of protein No. of genes ~ 30 000 ~35-000 37 Gene density ~ 1/100 kb 1/0.45 kb
Table continued.Very littleRepetitiveDNAOver50%ofgenomeTranscriptionThe greatbulk of genesareCo-transcription oftranscribed individuallymultiple genes from boththe heavy and light strandsIntronsAbsentFound inmostgenes~1.5%~93%% of coding DNACodon usageSlightlydifferentseeslideRecombinationAt leastonceforeach pairNoevidenceforthisof homologs at meiosisoccurring naturallyInheritanceMendelianforsequenceonExclusivelymaternalX and autosomes; paternalfor sequence onYS
19 Table continued. Repetitive DNA Over 50% of genome Very little Transcription The great bulk of genes are transcribed individually Co-transcription of multiple genes from both the heavy and light strands Introns Found in most genes Absent % of coding DNA ~ 1.5% ~ 93% Codon usage Slightly different see slide Recombination At least once for each pair of homologs at meiosis No evidence for this occurring naturally Inheritance Mendelian for sequence on X and autosomes; paternal for sequence on Y Exclusively maternal
Replication and TranscriptionReplicationstartswiththeHstrandHSFLSPTheoriginofreplicationfortheHstrandisirOHtheDloop,initiatedbyanRNAprimertRNAPhegeneratedfromtheL strandtranscript.tRNAThrDlooptRNA ValARN12SCytbAfterthenewHstrandisabout2/3complettheLstrandoriginofreplicationisuncovered.TheLstrand originisontheoldtRNAPrOARN16SND6HstrandND5tRNAGIUtRNA LOUTheL strandorigin folds into a stem-loopTERstructure.whichactsasaprimer.andIRNALeUIRNASereplicationoftheLstrandbeginsND1tRNAHIsHumanmtDNAReplicationcanbesaidtobebidirectionalb tRNAtRNAGIn16568bpND 4asynchronous,unlikereplicationofnuclearIRNAAlatRNA MetDNA,whichproceedsinbothdirectionsND2RNAASntRNACyssimultaneously.ND4LtRNATyrLight strandtRNAArgtRNA SertRNATrpND3TranscriptionCOX1OLtRNA GlyBothstrandsaretranscribedCOX3ATPase6COX2TheDloopcontainsonepromoterforeachATPase8Heavy strandtRNAASDstrand,andtheentirestrandistranscribedtRNA LysTheRNAisthencutintoindividual RNAsforeachgene.Protein-coding genes are given poly-A tails,20andrRNAandtRNAmoleculesaremodifiedasnecessary
20 Replication and Transcription • Replication starts with the H strand. – The origin of replication for the H strand is in the D loop,initiated by an RNA primer generated from the L strand transcript. – After the new H strand is about 2/3 complete, the L strand origin of replication is uncovered. The L strand origin is on the old H strand – The L strand origin folds into a stem-loop structure, which acts as a primer, and replication of the L strand begins. – Replication can be said to be bidirectional by asynchronous, unlike replication of nuclear DNA, which proceeds in both directions simultaneously. • Transcription. – Both strands are transcribed. – The D loop contains one promoter for each strand, and the entire strand is transcribed. – The RNA is then cut into individual RNAs for each gene. – Protein-coding genes are given poly-A tails, and rRNA and tRNA molecules are modified as necessary