EXSC%223:%Week%of%9/5/16%%Notes%from%the%textbook%Ch.%3.9%&%3.11%3.9$The$nucleus$includes$the$nuclear$envelope,$the$nucleolus,$and$chromatin$• Nucleus$o Average$size:$5µm$diameter$o Larger$than$any$cytoplasmic$organelle$o Usually$spherical$or$oval$o 3$regions$§ nuclear$envelope$(membrane)$§ nucleoli$§ chromatin$• nuclear$envelope$o double$membrane$separated$by$a$fluid-filled$space$(like$mitochondria)$o outer$nuclear$membrane:$continuous$with$the$rough$ER,$studded$with$ribosomes$o inner$nuclear$membrane:$lined$by$nuclear$lamina$§ lamina=network$of$lamins$(rod$shaped$proteins$that$form$intermediate$filaments)$that$maintains$the$shape$of$the$nucleus$o nuclear$pores$cover$nuclear$envelope$§ nuclear$pore$complex$lines$each$pore$§ regulate$entry$and$exit$of$molecules$o selectively$permeable$• nucleoplasm$o jellylike$fluid$in$nucleus$o holds$nuclear$elements$like$the$cytoplasm$does$o contains$dissolved$salts,$nutrients,$other$solutes$• nucleoli$o ribosomal$subunits$assembled$here$o not$membrane$bound$o typically$1-2$nucleoli$per$nucleus$o large$in$growing$cells$• chromatin$o composed$of:$§ 30%$DNA$§ 60%$histone$proteins$• cluster$of$8$of$them$form$a$nucleosome$that$the$DNA$wraps$around$• package$and$regulate$DNA$§ 10%$RNA$chains$$3.11$Messenger$RNA$carries$instructions$from$DNA$for$building$proteins$• DNA=master$blueprint$for$protein$synthesis$• Proteins=made$up$of$polypeptide$chains$o Polypeptide$chains=made$up$of$amino$acids$• Gene:$segment$of$a$DNA$molecule$that$carries$instructions$for$creating$one$polypeptide$chain$• Nucleotides$bases$o A,G,T,C$o Triplet:$sequence$of$three$of$the$bases$§ Ex/$AAA,$CGT,$TAC$o Variations$in$their$arrangement$allow$the$creation$of$different$kinds$of$proteins$• Exons:$informational$sequences$of$a$gene,$coding$region$• Introns:$noncoding$regions$of$DNA$• RNA$o function:$decode$and$transport$the$message$of$DNA$because$it$can’t$leave$the$nucleus$but$RNA$can$DNA%RNA%Sugar:$deoxyribose$Sugar:$ribose$Double-stranded$Single-stranded$Has$uracil$as$a$base$Has$thymine$as$a$base$$• types$o Messenger$RNA$(mRNA):$carries$the$coded$information$from$the$nucleus$to$the$cytoplasm$where$protein$synthesis$will$occur$o Ribosomal$RNA$(rRNA):$with$the$help$with$proteins,$forms$ribosomes$(sites$of$protein$synthesis)$o Transfer$RNA$(tRNA):$carry$amino$acids$to$the$ribosomes$where$they$decode$the$mRNA’s$message$for$the$amino$acid$sequence$in$the$polypeptide$to$be$built$• All$types$are$formed$in$the$nucleus,$using$DNA$as$the$template$o DNA$unzips$o One$strand$used$as$a$template$to$form$a$strand$of$RNA$with$complementary$bases$o RNA$moves$into$the$cytoplasm$through$a$nuclear$pore$(it$can$fit$because$it$is$single$stranded$vs$DNA$which$is$double$stranded)$• Steps$of$polypeptide$synthesis$o Transcription:$DNA’s$information$is$encoded$in$mRNA$o Translation:$information$carried$by$mRNA$is$decoded$and$used$to$assemble$polypeptides$$Lecture%Notes%on%9/7%$• Microtubules$and$microfilaments$function$in$cell$motility$by$interacting$with$motor$molecules$o Motor$molecules$can$attach$to$receptors$• Chemotaxis:$movement$of$an$organism$in$response$to$a$chemical$stimulus$Mitochondria$• Cellular$power$plants$• Site$of$oxidative$metabolism$o ADP$+$PàATP$• Mitochondria$density$in$a$cell$reflects$the$energy$requirements$o Very$active$cell=more$mitochondria$• Self$replicating$• Contains$its$own$DNA$o Encodes$13$proteins$o Maternal$• Enclosed$by$2$membranes$o Outer=smooth$o Inner=folds$(“cristae”)$o Matrix$is$site$of$ATP$synthesis$Summary$• Cells$are$not$just$bags$with$organelles$• The$cytoskeleton$o Maintains$integrity$of$the$cell$o Aids$in$movement$§ Of$organelles$within$the$cell$§ Of$the$cell$itself$****READ%section%on%cellular%extensions%(p89-91)%before%the%exam****%Cells$form$tissues$and$organs$by$“holding$hands”$• Specialized$membrane$proteins$help$cells$hold$onto$one$another$o Cellular$adhesion$molecules$(CAMs):$glycoproteins$that$help$cells$to$bind$at$junctions$• Membrane$junctions$o Tight$junctions$§ Impermeable$junction$that$encircles$the$cell$§ Prevent$molecules$from$passing$through$the$extracellular$space$between$adjacent$cells$§ Ex:$blood-brain$barrier$separates$the$brain$from$the$body$§ Interlocking$junctional$proteins:$claudins$and$occludins$o Desmosomes$§ Anchoring$junctions$scattered$along$the$sides$of$cells$§ Form$an$internal$tension-reducing$network$of$fibers$§ Parts$of$a$desmosome:$• Plaque$• Linker$proteins$• Intermediate$filaments$• Plaque$anchors$linker$proteins$to$the$intermediate$filaments$§ Linker$proteins$fit$together$like$a$zipper$in$the$extracellular$space$§ Ex:$many$are$prevalent$in$the$heart$and$skin$because$they$are$under$constant$mechanical$stress$o Gap$junctions$§ A$nexus$that$allows$chemical$substances$to$pass$between$cells$§ Communication$between$cells$§ Cells$connected$by$channels/pores$called$connexons$§ Selectivity$of$substances$varies$§ Ex/$Cardiomyocytes:$synchronize$electrical$activity$and$contraction$o Membrane$junctions$allow$cells$to$§ Hold$onto$each$other$to$form$sheets$§ Make$water$tight$seals$§ Communicate$Cell$to$cell$communication$• Hormone$receptors$o Method$for$the$cell$to$interact$with$its$environment$o Ex/$fat$cells$secrete$leptin$(signal)$to$the$brain$which$binds$to$leptin$receptors$in$the$brain$which$then$sends$a$message$to$the$body$that$you$are$full$o Very$selective$(i.e.$leptin$receptors$only$bind$leptin)$o Diverse$group$of$integral$proteins$and$glycoproteins$that$serve$as$binding$sites$(because$everything$has$to$have$its$own$binding$site)$o Response$varies$for$each$cell$type$§ Ex/$acetylcholine$stimulates$skeletal$muscle$but$inhibits$cardiomyocytes$• Receptor$mediated$second$messenger$system$o Ligand$(1st$messenger)àreceptoràG$proteinàenzymeà2nd$messenger$o Ligand$binds$to$the$receptor$o Activates$G$protein$with$GTP$(similar$to$ATP)$o G$protein$activates$or$deactivates$effector$protein$(ex/$an$enzyme)$by$causing$its$shape$to$change$o Effector$catalyzes$reaction$that$produces$2nd$messengers$in$the$cell$o 2nd$messenger$carries$out$instructions$Build/remodel/demolish$• DNAàRNAàprotein$• Cells$make$proteins$for$structural$or$enzymatic$reactions$• Transcription$o mRNA$o splicing$• Translation$o rRNA$tRNA$o modification$o packaging$$o secretion$• Demolish/recycle$o