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45 Cards in this Set

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Name the structural elements of thecytoskeleton.

The 3 structural elements of thecytoskeleton are:-


1. microfilaments,


2.intermediate filaments,


3. microtubules.

Size of Microfilaments

Microfilaments are 6 to 8 nm in diameter

What do microfilaments cosist of?

Microfilaments consistof globular actin molecules polymerized into long filaments

Cultured osteogenic cells labeled with an antibody to actin, the main protein constituting microfilaments, usingthe fluorescence technique (nuclei are stained using DAPI [4,6-diamino-2-phenylindole] and appear blue).

#Nomarski differential interferencecontrast image of microfilament bundles in the cytoplasm of cultured fibroblasts from the pig periodontal ligament.


#Nomarski images are producedby using the interference conditions generated by optical-path-length differences of two beams of coherent light.


#The microfilamentbundles appear as elongated, raised lines

Electron micrograph of microfilaments in the cytoplasm of a fibroblast. MF, Microfilaments; M,mitochondria; N, nucleus.

Function of Microfilaments

Microfilaments form tracks for themovement of myosin and serve as intracellular “muscles”for maintenance of cell shape, movement, and contractility.

Where are Microfilaments found?

Microfilament networks, (along with actin-binding andactin-bundling proteins,)


#are found in association withadhesive cell junctions, as a “web” beneath cell membranes,especially the apical membrane,


and as the


#structural “core”of microvilli, filopodia, and lamelipodia.


NOTE: Actin interactswith the other two components of the cytoskeleton.

Size of Intermediate filaments

Intermediate filaments are approximately 10 nm in diameter.

Function of Intermediate filaments

#Intermediate filaments are important in the maintenance of cellshape and contact between adjacent cells and the extracellularmatrix.


#In cells of mesenchymal origin, such as fibroblastsand osteoblasts, intermediate filaments are polymersof the protein "Vimentin "




#In epithelial cells, intermediatefilaments consist of cytokeratins. The filaments formbundles, called tonofilaments, which anchor onto desmosomes

Presentation of Intermediate filaments in cells of mesenchymal origin.

In cells of mesenchymal origin, such as fibroblastsand osteoblasts,


intermediate filaments are polymersof the protein vimentin

Presentation of Intermediate filaments in epithelial cells

In epithelial cells, intermediatefilaments consist of cytokeratins.




The filaments formbundles, called tonofilaments, which anchor onto desmosomes

 

#(Pic...) Intermediate filaments in cultured osteogenic cells stained for vimentin by the immunofluorescence method



# In cells of mesenchymal origin, such as fibroblasts and osteoblasts, intermediate filaments are polymers of the protein vimentin

#(Pic..)Electron micrographs of intermediate filaments; these form discrete bundles, called tonofilaments (Tf), that insert into the desmosomalplaques (DS) or distribute around the periphery of a cell.



#In epithelial cells, intermediate filaments consist of cytokeratins. The filaments form bundles, called tonofilaments, which anchor onto desmosomes



#(Pic..)Basal cell of a salivary gland excretory duct; hemidesmosomes form attachmentsto the basal lamina surrounding the duct.




# In epithelial cells, intermediate filaments consist of cytokeratins. The filaments form bundles, called tonofilaments, which anchor onto desmosomes

How do Cytokeratins help in the detection of origin of various tumors?

#Cytokeratins are a multigenefamily of proteins made up of basic and more acidic proteins.


#Cytokeratins occur as linked acidic and basic pairs with differingcombinations in different types of epithelia.


#Theirexpression patterns have been used to determine the relationshipbetween cell types and as an indication of the originof various tumors.

Size of Microtubules

Microtubules are tubular or cylindrical structures with anaverage diameter of 25 nm

Describe the structure of Microtubules

#Microtubules are tubular or cylindrical structures with anaverage diameter of 25 nm.


#Microtubules arecomposed of the protein tubulin


#They are arranged in rings stackedend to end, making up the tubules.

#(Pic..)Microtubules. A, Fluorescent micrograph of cultured osteogenic cells labeled with an antibody to tubulin, the main protein ofmicrotubules. Under the fixation conditions used here, the microtubules are seen as unpolymerized tubulin (dotted immunofluorescencepattern).





Longitudinally oriented Microtubule

Cross section of Microtubules

Functions of Microtubules

1.Microtubules provideinternal support for the cell;




2. They are the basis of motility forcertain organelles, such as cilia;




3. They act as guide paths and partof the motor mechanism for the movement of secretoryvesicles and other organelles;




4.They serve to position certainorganelles within the cell.

Classify intercellular junctions.

1. Tight junctions (zonula occludens)




2. Adhesive junctions


a. Cell-to-cell


i. Zonula adherens


ii. Macula adherens (desmosome)




b. Cell-to-matrix


i. Focal adhesions


ii. Hemidesmosomes




3. Communicating (gap) junctions

What type junction does the term zonula describe?

The term Zonula describes a junction that completelyencircles the cell;

What type junction does the term macula describe?

Macula indicates a junction that is more circumscribed in extent (e.g., patchlike).

Components Intercellular junctions

On the molecular level, intercellularjunctions typically consist of three components:




1.A transmembraneadhesive protein,


2.A cytoplasmic adapter protein


3.Acytoskeletal filament.




These three components differdepending on the type of junction.

Another name for Tight junctions

Tight junctions =zonula occludens

The picture shows an Electron micrograph of a junctional complex
between epithelial cells of a salivary gland.
Label the 3 parts

The picture shows an Electron micrograph of a junctional complexbetween epithelial cells of a salivary gland.


Label the 3 parts



A. Tight junction /zonula occludens; (top most).


It is located at the boundary of the apical andlateral cell membranes, the intercellular space is obliterated.


B. Zonula adherens (middle) :


In theadherens junction (zonula adherens, ZA), the cell membranes areseparated by approximately 20 nm, and a dense mat of microfilamentsis present in the cytoplasm.




C. Desmosome (lowermost):


In the desmosome (DES), the cellmembranes are parallel and separated by approximately 25 nm,and a central dense line is present in the intercellular space. Intermediatefilaments insert into dense plaques on the cytoplasmicsurface of the desmosome.

Explain the structure of tight junctions.

#In occluding, or tight junctions the opposing cell membranes are held in close
contact by the presence of transmembrane adhesive proteins
arranged in anastomosing strands that encircle the cell. #The
intercellular space essentially is obliter...

#In occluding, or tight junctions the opposing cell membranes are held in closecontact by the presence of transmembrane adhesive proteinsarranged in anastomosing strands that encircle the cell. #Theintercellular space essentially is obliterated at the tight junction.


#The transmembrane adhesive proteins interact homotypically withthe same proteins on the adjacent cell. (Egs occludin, members of the claudin family, and in some tissues, junctional adhesion molecule)


#Several cytoplasmicproteins associate with the intracellular portions of thetransmembrane proteins;( these include cell polarity–relatedproteins, vesicular transport–related proteins, kinases, transcriptionfactors, and a tumor suppressor protein.) #In addition,some of the cytoplasmic proteins of the tight junctionsbind to actin filaments.

What are the functions of Tight Junctions?

*Tight junctions control the passageof material through the intercellular spaces (e.g., from theinterstitium to the lumen of a gland).


*They also have animportant role as a “fence” to define and maintain the twomajor domains of the cell membrane, the apical and basolateral surfaces.



What does the permeability of tight junctions depend on?

*The permeability or “tightness” of the junction to waterand ions (especially cations) is related to the specificclaudin(s) present and is correlated with the number ofstrands of transmembrane proteins.



*For example, tight junctionsjoining salivary gland secretory cells have only two orthree junctional strands and are relatively permeable towater, whereas those joining salivary gland striated duct cellsmay have six to nine strands and are relatively impermeableto water.


*The permeability of tight junctions in some tissuesmay be regulated by certain neurotransmitters andhormones.

What are Adhesive junctions?

Adhesive junctions hold cells together or anchor cells tothe extracellular matrix.

How much inter-cellular space is maintained between two adhesive junctions?(approx)

The inter-cellular space in cell-cell adhesive junctions is maintainedat approximately 20 nm.

What are the functions of Adhesive Junctions?

#Adhesive junctions also areimportant in cellular signaling.




#Their cytoplasmic componentsmay interact with the cytoskeleton, triggering changesin cell shape or motility, or with certain tumor suppressormolecules, or they may act as nuclear transcription factorsor coactivators.




#In some instances, the loss of cell-cell orcell-matrix contact may lead to apoptosis (programmed celldeath), whereas in others, loss of contact may lead to loss ofcell polarity and differentiation or unregulated cell proliferation.

In Adhesive junctions, what are the principal transmembrane proteins?

In cell-cell adhesive junctions the principal transmembraneproteins are members of the cadherin family.


Cadherinsare calcium ion–dependent proteins that interact homotypicallywith cadherins on the adjacent cell.

In Adhesive junctions, what are the principal cytoplasmic adapter proteins?

The cytoplasmicadapter proteins are members of the catenin family.


Catenins interact with the cytoplasmic domain of the transmembranecadherin molecule, with the cytoskeleton, and with a numberof other proteins, including kinases, and tumor suppressormolecules that are associated with adhesive junctions.

Wit respect to Zonula adherens name the following:


a) Cadherin family member




b) Cytoplasmic adapters




c) Cytoskeletal component

In thezonula adherens,


a) Cadherin family member= E-cadherin




b) Cytoplasmic adapters= α- and β-catenin




c) Cytoskeletal component= Actin filaments



Explain the structural arrangement of catenins and actin filaments in the Zonula adherens.

The catenins and actin filaments are concentratedon the cytoplasmic side of the cell membrane at thezonula adherens to form a dense web that is continuous withthe terminal web of actin at the apical (and sometimes thebasal) end of the cells.

Name the cytoplasmic proteins associated withthe zonula adherens and state their functions.

1.E-cadherin, α- and β-catenin : the cytoplasmicadapters


2. Actin filaments: cytoskeletalcomponents


3.Nectin: It establishes the initialadhesion site and recruites E-cadherin and other proteinsto the junction.


4.p120 catenin: a signaling moleculeassociated with E-cadherin that is important in stabilizingthe junction;


5.Afadin: It links nectin to the actincytoskeleton;


6.Vinculin and α-actinin: They are actin-bindingproteins;


7.Ponsin: links afadin and vinculin

Name the cadherins present in desmosomes




(T51)

The cadherins present in desmosomesare:-


i) Desmoglein and


ii) Desmocollin.

What is the result of the interaction between desmoglein,desmocollin and the adjacent cell wall?




(T51)

In the desmosome, the cadherinsare desmoglein and desmocollin.


The interaction ofthese transmembrane proteins with those from the adjacentcell results in a dense line in the middle of the intercellularspace at the desmosome.

Name the catenins present in desmosomes




(T51)

The catenins present in desmosomes are:-


i)Desmoplakin,


ii)Plakoglobin,and


iii)Plakophilin

State the functions of desmosomal catenins




(T51)

#The desmosomal catenins are desmoplakin, plakoglobin,and plakophilin.




#They form an electron-denseplaque on the cytoplasmic side of the desmosome.


#Thisplaque serves as an attachment site for the cytoskeletal components,which in the case of the desmosome are intermediatefilaments.

What are Integrins




(T51)

Integrins are heterodimers of different alpha andbeta subunits that occur in different combinations withspecificity for various extracellular matrix molecules

Name Cytoplasmic adapter proteins and state their function




(T 52)

Cytoplasmic adapter proteins, which include the actinbindingproteins are:-


i) α-actinin,


ii)vinculin, and


iii) talin




Function: They link thetransmembrane integrins to the actin cytoskeleton.