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T/F: cell junctions are relatively permanent and strong sites of cell-cell and cell-ECM attachment

True

What are the four classes of cell junctions?

1. anchoring
2. occluding
3. channel forming
4. signal relaying

What is the function of anchoring junctions?

to attach the cytoskeleton of one cell to the cytoskeleton of another cell or to the ECM

What is the basic design of anchoring junctions?

actin or intermediate filaments bind to attachment proteins on a different cell that are attached to transmembrane glycoproteins or to the ECM

What are the four forms of anchoring junctions?

1. adherens junction(cell-cell)
2. desmosome (cell-cell)
3. actin linked cell-matrix adhesion (cell matrix)
4. hemidesmosome (cell matrix)

What is a cadherin and what does it attach to?

a cadheren is a calcium dependent, homophillic glycoprotein (binds to other cadherin) transmembrane adhesion protein found in adherens junctions

Describe the cadherin family

a complex superfamily of proteins with diverse expession patterins. regulation of cadherin expression is important in developing tissues, especially in the epithelial-mesenchymal transition

What type of intracellular cytoskeletal attachment to adherens junctions utilize?

cadherins bind to catenins which bind to actin

Where are adherens junctions usually located?

in many epithelia, they are located near the apical surface or the ADHESION BELT OR ONULA ADHERENS

zonula adherens or adhesion belt

adherens junction

epithelial mesenchymal transition

different cadherins are expressed at different time during neural tube differentiation

Which cadherins are usualy used in adherens?

E, N, P, VE

catenins

used in adherens junctions. bind to cadherins and actin

What is the function of adherens junctions?

use actin to utilize purse string contraction involved in morphogenetic movements (invaginations, formations of tubes)

What is the primary function of desmosomes?

act to provide mechanical integrity to tissues

Describe desmosomes

button like plaques on lateral surfaces of epithelial cells

T/F: desmosomes are involved with cadherens as well

True

desmoglein or desmocollin are what?

cadhereins associated with desmosomes

Describe the desmosomal connections

desmosomes connect to desmoglein/desmocollin which connect to plakoglobin, plakophilin and desmoplakin intermediate filaments(keratins-epithelia or desmin-cardiomyocytes

plakoglobin, plakophilin, and desmoplakin

connect to desmosomal cadherins (desmoglein and desmocollin) in desmosomes

What is pemphigus?

autoimmune skin blistering disease

what causes pemphigus?

individuals with this disease develop antibodies against desmosomal cadherins (desmoglein) in their skin resulting in desmosomes being disrupted. this causes blistering because the skin cells are not firmly attached to one another.

What are integrins main functions?

most of them act as cell-MATRIX adhesion molecules. control cell survival and proliferation in response to binding to ECM- can recruit intracellular signaling molecules

describe the structure of integrins

transmembrane heterodimers with multiple combinations

What minerals do integrins need in order to bind to ECM?

calcium and magnesium?

focal adhesions

actin linked cell-matrix adhesions

Describe the basic design of focal adhesions

integrins (on a cell surface) bind to linker proteins (talin and vinculin) which then bind to the Actin cytoskeleton

describe integrin regulation

integrin activity can be moduled by factors outside of the cell or inside the cell. integrins can switch between active and inactive conformation-important for cell motility( integrins activated by g protein coupled receptor and tyrosine kinase)

major function of hemidesmosome

attach the basal surface of epithelial cells to the ECM (basal lamina). provide mechanical integrity to many epithelia

Describe the connections of hemidesmisomes

a6b4 integrin connects the ECM to the keratin intermediate filaments. a6b4 integrin binds to linker protein (plectin and dystonin) which connects to keratin intermediate filaments which connects to ECM

plectin

linking protein for hemidesmisomes to keratin intermediate filaments

dystonin

linking protein for hemidesmisomes to keratin intermediate filaments

T/F: the orientation of the interaction of the intermediate filaments in hemidesmisomes and desmisomes is the same

False, it is lateral in desmisomes and direct in hemidesmisomes

epidermolysis bullosa

a genetic disease in which the attachment of the basal cells to the epidermis between the epidermis and dermis is interrupted. results in blisters and very fragile skin. problem with hemidesmisomes: could be defect in integrin, keratin, or laminin)

zona occludens

occluding or tight junction

tight junction

occluding junction

function of tight junctions?

anchor epithelial cells to one another while acting as a selective barrier to diffusion of molecules between cells and to proteins in plasma membrane. confer polarity to epithelial cells (apical and basolateral). paracellular transport and transcellular transport

Where are tight junctions usually formed?

near the apical surface of the epithelial cells

Describe the basic design of tight junctions

many strands formed by transmembrane junctional proteins that bind each other and form the seal. the more strands the tighter the seal. require calcium.

claudins

major transmembrane proteins which link to the actin skeleten through zona occludens (adherens junction) proteins

occludins

major transmembrane proteins which link to the actin skeleten through zona occludens (adherens junction) proteins

paracellular transport

function of tight junctions-selective permeability barriers

What regulates cell polarity?

adherens junctions, tight junctions, and basal lamina

Gap junctions usually located where?

below adherens junction

connexins

channel forming proteins used by gap junctions. make connexon. can form hetero and homo heamers with different biochemical properties

What is the function of gap junctions?

allow selective passage of small molecules between cytoplasm of neighboring cells. coupling of cells electrically and metabolically. permeability can be regulated (generally by Mw)

infertility

can be caused by a mutation in connexin 37. ovarian follicle development depends on gap junction mediated communication between the oocyte and surround granulosa cells. connexin 37 is important for the exchange of nutrients and signals in oocyte maturation

signal relaying junctions

utilize adherens and focal adhesions

selectins

transmembrane proteins that bind to carbs on cell surfaces. heterophellic. calcium INDEPENDENT. involved in leukocyte trafficing (weak adhesion and rolling)

integrins

aLB2 expressed on leukocytes and T-cells, involved in strong adhesion and extravasation. interaction between t-cells and antigen presenting cells

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