Cell junctions : types and plasmodesmata

Cell junctions

1. Cell
junctions
Submitted to,
Dr. Arya P Mohan
Asst.Professor
St.Teresa’scollege,
Ernakulam
Submitted by,
AncyVarghese
I MSc Botany
Roll no . 6
1

2. Overview
•Introduction -3
•Overviewofjunctions–4
•Occludingjunctions. –5
•Anchoringjunctions -8
1.Adherensjunctions–9
2.Desmosomes –10
3.Hemidesmosomes –11
•Communicatingjunctions-15
•Plasmodesmata -17
•Reference -19

3. Why cell Junctions are formed?
•Cellsdonotliketoliveinisolation.
•Formationofmulticellularorganismsrequirespecificinteraction
betweencellstoholdthecellstogetherandtocommunicateinorder
tocoordinateactivities.
•Celljunctionsarestructureswherelongterm,permanentassociation
betweencellsareestablished.
•Mainly3typesofcelljunctions
1.Occludingjunctions
2.Anchoringjunctions
3.Communicatingjunctions
3

4. An overview of junctions
4

5. Occluding junctions Or Tight junctions
Subunits of tight junctions
5

6. 1.Occluding junctions / Tight junctions
•Acell-celljunction
•Sealscellstogetherinanepithelium.(Skin,
intestinallining.)
•Nospacebetweenplasmamembranesofadjacentcells.
•Preventsevensmallmoleculesfromleakingfromonesideofthe
sheettoother.
•Blocklateralmovementoflipids&membraneproteinstokeepa
cellpolarized.
6

7. Functions
•Givesstrengthandstabilitytothecell.
•Fencing(Protective)function.
•Maintainscellpolarity.
•Preventsflowofglucosebetweencells.
•Selectivelypermeableforions.
7

8. 2. Anchoring junctions –3 types
1.Adherensjunction
2.Desmosomes
3.Hemidesmosomes
8

9. a.Adherencejunction
•Acell-celljunction.
•Cadherinsarethecelladhesionmolecules.
•InteractionofCadherinisCalciumdependent.
•Cadherinattachwithactinfilamentviaspecificadaptorslikealpha
catenin,betacateninetc.
•WhenthereisenoughCa2+Cadheringetattachedtonearbycells&
formadherencejunctios.
9

10. b.Desmosomes
•Theyarebipartitestructuresofapposingcellmembranes.
•Anattachmentplaqueonthecytoplasmicsideanchors
tonofilamentswhichareintermediatefilaments.
•Desmosomesformstrongpointsofadhesionbetweencells
inatissuesuchthat2adjoiningcellsareseparatedbyathin
spaceof25-35nm.
•CelladhesionmoleculesareDesmosomalCadherins.
10

11. c.Hemidesmosomes
•Connectacell,throughaplaquetothebasallamina(ECM)by
integrins.
•AsinDesmosomes,Hemidesmosomesinteractwithtonofilament-
intermediatefilaments.
•Hemidesmosomesoccuratmostbasalsurfaceofstratifiedsquamous
epithelia,wherethesuperficiallayerlackjunctionalcomplexes&the
basalcellsareexposedtotheunderlyingcytoplasm.
11

12. Functions
•Providefirmstructural&mechanicalattachmentbetween2cellsor
betweenacellandECM.
•Responsibleforstructuralintegrityoftissue.
•DevelopingpolarityinNeuraltubeclosure.
•Imp.inpancreaticbranching.
12

13. Adherensjunction & Cancer formation
•IntumourcellsAdherensjunctionarenotpresent.
•Adherensjunctionproteinsareheavilydownregulated.
•So,tumourcellseasilygetsdissociated,travelthroughbloodsupply&
reachsecondaryorgansviametastasis.
•OverexpressionofCadherinproteinpreventthemtometastasize.
13

14. 3.Communicating junctions (Gap junctions )
Firstdiscoveredin
myocardium&nerve
cellsbecauseof
theirpropertiesof
electrical
transmission
betweenadjacent
cells.
14

15. Communicating junctions (Gap junctions)
•ACell-celljunction.
•Clustersofintercellularchannels,thatallowdirectdiffusionof
ions&smallmoleculesbetweenadjacentcells.
•Presentinheart,basalpartofepithelialcellofintestinal
mucosa…etc.
•Assitesofelectron-coupling(reducedresistancetoionflow),it
istheonlytypeofjunctionmediatingflowofcurrentbetween
cells.
•Junctionalunit-Connexins
•6proteinscalledConnexinsformaConnexon.
•2connexonsendtoendforma1.5nmchannelbetween2cells.
15

16. Functions
•Importantinintercellularcommunication
andcoordination.
•Allowspassageofions,cyclicAMP,amino
acids&othersmallmolecules.
•Synchronizingbeatofheartmusclecells.
•Rapidpropagationofactionpotential
fromonecelltoanother.
•Exchangeofchemicalmessagesbetween
cells.
•Cancercellsgenerallydonothavegap
junctions,sothatcellsfailtocommunicate
theirmitoticactivitytoeachother,which
mayexplaintheiruncontrolledgrowth.
16

17. Plasmodesmata
•Adherencebetweenplantcells–
mediatedbytheircellwallsratherthan
bytransmembraneproteins.
•Middlelamella–apectinrichregionof
cellwallactsasagluetoholdadjacent
cellstogether.
•Plantcellsdonotrequireformationof
cytoskeletallinks(desmosomes&
Adherensjunctionsofanimalcells)-due
torigidityofplantcellwall.
•FunctionisanalogoustoGapjunctions.
17

18. •Anextensionofsmooth
Endoplasmicreticulumpasses
throughthepore,leavingaringof
surroundingcytoplasm–through
whichionsandsmallmolecules
areabletopass.
•Plasmodesmataaredynamic
structuresthatcanopenand
closeinresponseappropriate
stimuli.
•Regulated passage of
macromoleculesispossible.
18

19. Reference
1.Lordish,H.,Berk,A.,Zipursky,S.,Matsudaira,P., Baltimore,D.,&
Darnell,J.(2016).Molecularcellbiology.NewYork:W.H.Freemanand
company.
2.Cooper,G.,&Hausman,R.(2007).TheCell:AMolecularApproach(4
th
ed.).Sunderland,MA:SinauerAssociates.
3.Karp,G.(2013).CellandMolecularBiology:Conceptsand
Experiments.NJ:JohnWiley&SonsInc.
4.www.slideshare.net.CellJunctions.,MrsOfeliaSolanoSaluder.
19