Bio$200$Lecture$13$$Protists/$marks$the$arrival$of$eukaryotes.$$$Eukaryotes/$Chemical$evidence$of$eukaryotes$as$far$back$as$2.7$BYA,$but$no$true$fossils$until$about$a$billion$years$later.$$/Originated$through$a$evolutionary$sequence$that$involved$many$steps:$• Origin$of$a$flexible$cell$surface$• Cytoskeleton$• Development$a$nuclear$envelope$that$enclosed$a$genome$that$organized$into$chromosome$• Evolution$of$digestive$vacuoles$• Engulfment$of$bacteria$that$lead$to$the$evolution$of$organelles$($a$theory$that$lead$to$endosymbiosis)$$$Traits.of.Eukaryotes:..Distinguished$from$prokaryotes$in$3$major$ways:$$• Multicellular,.(there.are.single.celled.eukaryotes.as.well,.but.the.majority.are.multicellular):.a) Multicellular$bodies$allow$organisms$to$deal$with$their$environment$in$new$ways$because$of$the$differentiation$of$cell$types$into$organs$and$tissues.$$This$allows$organisms$to$be$more$flexible$about$the$environments$they$encounter..• Capable.of.sexual.reproduction:.a) Sexual$reproduction$leads$to$increased$genetic$diversity=$RECOMBINATION$(promotes$dive rsity$and$po ten tially$increased $the$spee d$of$adap tation). .• Compartmentalized:.a) Eukaryotic$cells$have$organelles$that$carry$out$independent$functions$within$a$cell.$.b) These$organelles$were$developed$in$a$number$of$ways$including$a$membrane$infolding $as$well$as$engu lfin g$o th er $ce lls$a nd $h ijac k ing $th eir $fun c tio ns../The.modern.eukaryotic.cells.are.kind.of.a.cut.a.paste.job.of.genes.from.multiple.organisms.and.contain.structures.that.belong.to.prokaryotic.species...Loss.of.the.Cell.wall.&.Formation.of.Organelles:.• The$path$toward$eukaryotic$cells$must$have$begun$of$the$loss$of$the$rigid$eukaryotic$cell$wall.$This$allowed$the$more$fluid$plasma$membrane$to$fold$into$itself.$It$creates$more$surface$area$without$increasing$size.$This$allows$larger$surfaces$for$gas$and$nutrient$exchange.$Once$the$cell$surface$can$fold$in,$it$can$also$pinch$off$and$bring$items$fro m $o u ts id e$t he $ce ll,$in to $th e $ce ll= $endocytosis.$.• Once$the$membrane$is$folded,$new$structures$can$be$created.$$Both$the$nucleus$and$the$endopla sm ic $retic u lum$are$the$resu lt$o f$m e m b ra n e$in /fo ld in g.• The$DNA$of$prokaryotic$cells$is$attached$to$a$small$portion$of$the$plasma$membrane.$We$believe$this$region$of$attachment$in/folded$in$a $pr oc u rse r$to $th e$modern$$eukaryote,$taking$the$first$steps$towards$eternal$enclosure$DNA $in$a$nuclear$envelope.$$.• Once$the$free$floating$ribosomes,$they$attach$to$the$infolding$membranes,$this$is$the$pathway$to$the$modern$Endoplasmic$Reticulum..Endosymbiosis:.• Means$living$together$in$close$association.• An$ancestral$eukaryotic$cell,$this$cell$engulfed$aerobic$energy$producing$bacterium.$We$believe$it$was$a$purple$non/sulfur$bacteria$(Probacteria).$But$it$did$$not$digest$it.$Over$time,$this$arrangement$became$permanent$with$the$bacterium$being$unable$to$live$outside $the $eu k aryotic$cell,$and$the$eukaryotic$cell$being$dependent$on$the$bacterium.$$• Originally$the$bacterium$probably$detoxified$the$new$the$oxygen$that$the$cyanobacteria$was$flooding$the$atmosphere$with,$by$converting$it$to$water.$The$process$was$coupled$with$ATP$production$and$that$is$a$process$that$is$highly$dependent$on$oxygen.$The$end$result$is$modern$Mitochondria/$ATP/Energy$producing$powerhouse$of$the$cell.$$$• The$same$process$of$endosymbiosis$occurred$later$in$eukaryotic$evolution$with$the$engulfment$of$cyanobacteria.$$• The$cyanobacteria$then$became$the$chloroplasts$of$the$modern$plant$(photosynthe sis).$$• $Chloroplasts$show$an$unusual$form$of$HOMOLOGY$in$bacteria$a n d$in $p la n ts$b e ca u s e$of$this$endosymbiosis$event.$• The$eukaryotic$cell$is$a$fusion$of$genetics$for$multiple$spe cies $be ca u se$o f$th is$extreme$version$of$Horizontal$Gene$Transfer.$By$looking$at$the$pattern$of$which$organisms$have$mitochondria$and$chloroplasts,$we$can$determine$$when$the$these$endosymbiosis$events$happen$in$evolution$history.$$.$.....................EukaryotesM.Begins$with$ancestral$protists.$These$organisms,$they$diverge$in$a$world$that$was$shifting’s$between$anaerobic$and$aerobic$conditions,$which$really$opened$up$a$lot$of$opportunities$for$new$organisms$to$evolve,$such$as$cellular$respiration/$most$efficient$ways$of$producing$energy.$$Protists:$$• As$a$group,$only$truly$unified$by$all$having$organelles.$Protists$are$very$diverse,$far$more$diverse$than$plants,$fungi$and$animals.$$$• Both$unicellular,$multicellular,$colonial,$asexual,$sexual$protists.$$$• Descriptive$of$a$world$in$transition$$$• The$results$of$evolution$during$the$rise$of$Eukaryotes$are$hugely$diverse.$Some$authors,$replace$the$word$“protists”$with$“microbial$eukaryotes”,$really$to$indicate$this$isn’t$a$monophyletic$group.$$• The$genetic$relationship$among$the$protest$and$the$most$recent$common$ancestor$of$all$the$protists$groups$are$also$the$most$recent$common$ancestor$of$all$eukaryotes.$Eukaryotes$are$monophyletic,$so$this$makes$the$protists$paraphyletic.$$$$$$$$$$$$$$$$Cdddd$$Some$protists$are$very$closely$related$to$fungi$and$animals$than$to$other$protists,$and$similarly$with$plants.$This$makes$the$protests$highly$paraphyletic.$$.$This$eukaryotic$tree$shows$the$hypothesis$for$the$relationships$among$eukaryotes:$$5.main.groups.from.the.tree:.• The$SAR,$all$contains$protists..• The$Excavates,$all$protists..• The$Archaeplastida,$land$plants/algae$..• The$Amoebozoans,$all$protists..• The$Opisthokonts,$Fungi$and$animals.../All$of$these$groups$are$monophyletic$clades.$$/Taxonomy$doesn’t$equal$phylogeny!$This$tree$highlights$this.$The$naming$of$groups$doesn’t$follow$evolutionary$relationships$$..Traits.of.Protists:..• Un/unified$group$of$organisms=Protists$• Variation$in$protist’s$traits$reveal$the$lack$of$unity$in$this$group.• Locomotion:.§ protists$can$move$using$flagella$Ex:Euglena..§ Protists$can$move$using$cilia$(groups$of$short$flagella$like$protrusions$that$wave$creating$water$currents).§ Protists$can$move$using$pseudopodia$(use$variously$shaped$sticky$protrusions$that$reach$out$and$stick$ t o$adjacent$surfaces,$basically$rolling$the$protisit$across$the$surfaces)$EX:$Amoeba.• Cell$Surface:$a) Some$protists$are$only$surrounded$by$plasma$membrane,$but$many$other$protists$have$extra$cellular$material$that$is$deposited$on$this$membrane.$EX:$Amoeba.$$b) This$extra$cellula
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