LEC38: Cells in Tissues: Junctions, Adhesion, and Extracellular Matrix Flashcards Preview

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Flashcards in LEC38: Cells in Tissues: Junctions, Adhesion, and Extracellular Matrix Deck (44):

what is epithelia

majority of cell in body are epithelia 

line channels on inside and outside of body - i.e. in pancreas, gut, skin 

form sheets, display polarized structure, w/ apical border exposed or lining channel and basal surface on basal lamina 


are epithalial cells polarized


polarization maintained by specialized cell junctions that bind the cells to each other, help separate distinct membrane domains


kinds of cells in body


connective tissue

muscle cells

nervous cells

blood cells


ell adhesion moecules

1) cadherins 

2) IG superfamily 

3) integrins

4) selectins


homophilic vs heterophilic binding

homophilic- same adhesion molecule binding (i.e. cadherins) 

heterophilic- diff molecules (integrins on the cell, laminin on ECM)


cell adhesion molecule functions inside cells

1) inside cells, bind to adapter proteins that interact w/ cytoskeleton, thereby connecting outside of cell to cellular machinery:

binding regulates cell migration, cell proliferation, cell death 

2) associate in clusters in a lateral fashion, creating junctions of cell adhesion molecules 


ECM functions

1) hold tissues together - multiadhesive proteins

2) provide cushioning (cartilage) and strength (tendons) - via proteoglycans 

3) acts as reservoir for growth factors 

4) resist tensile/stretching forces via proteins like collagen


what comprises ECM?

proteins and carbohydrates such as proteoglycans 

all ECM components are highly networked w/ each other, and w/ receptors on cell surface, i.e. integrins 

composition of ECM varies by tissue


purpose of epithelial cells' polarized cellular organization

divide body cavities, provide barriers between gut and blood and blood brain barrier 

polarization allows for diff functions like absorption of nutrients on 1 membrane, secretion from another membrane 


what is on apical surface of epithelial cells


for absorption


cell junctions in epithelial cells

1) tight junctions 

2) anchoring junctions: adherens, desmosomes, hemidesmosomes

3) communicating junctions: gap junctions

4) integrins


tight junctions function? structure?

exist directly under microvilli 

seal epithelial cells together in sheets

prevents passage of small molecules 


tight junctions made of?

claudins, occludins


anchoring junctions function

join cells to each other and to ECCM

1) adherens junctions and desmosomes

2) focal adhesions and hemidesmosomes



adherens junctions and desmosomes functions

made by homophilic interactions among cadherens

hold cells together by connecting to a linker protein, alpha and beta catenin, in the middle of cytoskeletons of 2 cells 

impact polarity of epithelial cells also 


nature of caderins throughout the body?

tissue specific localizations - diff kinds of cadherins in diff parts of the body

cancer cells can move throughout the body if/when they lose their specific cadherins 


focal adhesions?

integrin proteins that bind to the ECM outside and attach to actin inside the cell 

controls interaction of integrin w/ the ECM, outside of cell 

impact physiological processes


desmosomes connect with what?

anchoring junctions that connect with cadherins and IF, so bind indirectly to actin



hemidesmosomes are made of?


bind inside the cell, and to the ECM via integrin


gap junctions function?

cell - cell communication 

allwo for electrical coupling between cells


what are cadherins

what does their loss result in

large glycoproteins that link by a homophilic (same cadherin) mechanism 

link to actin cytoskeleton via adapter proteins, catenins (alpha and beta catenin) 

disruption of cytoskeletal interaction via adapters -> loss of adhesion


integrins function

cell matrix receptors on cells 

are abdunant on cell surfaces, bind ligand w/ low affinity 

activate signaling pathways upon ligand binding 

comprise alpha and beta subunits held together noncovalently

Ca2+ or Mg2+ needed for ligand binding


what integrain is a hemidesmosome connection

a6b4 interacts w/ IFs a hemidesmosomes 

exception to integrins connecting to bundled actin filaments


what mediates actin-integrin interaction

anchor proteins - talin, a-actinin, filamin 

linkage leads to clustering and formaiton of focal adhesions


what are selectins?

lectins (carb binding) that media Ca2+-dependent cell-cell adhesion in bloodstream 

L-selectin in WBC, P-selectin in platelets 

each binds to a specific carb on another cell 


how do WBC travel around the blood

during inflammation, endothelial cells express E-selectin 

as travel around blood, WBC bind to an epithelial cell via selectins (i.e. E-selectin), selectins collaborate w/ integrtins

WBC then roll over cells til get to integrins, where WBC are stopped, and go through endothelial cells and into tissue 

so selectins mediate weak binding at first, integrins mediate strong binding to WBC


what is ECM

space between cells 

a misture of proteins and polysaccharides 

high ECM in bone and cartilage, low ECM in brain and spinal cord


what forms bone/teeth

calcified ECM


how is ECM in tendon



what is basal lamina

form of the ECM at interface of epithelia and connective tissues


where is basal lamina found

underlies epithelial cell sheets and tubes 

around muscle cells, fat cells, schwann cells 

separates these cells from CT and serves as highly selective filter


what does basal lamina influence

cell polarity, metabolism, survival, proliferation, idfferentiation 

serves as highway for migration


what forms BL

cells that sit on it


what is basement membrane

structure connected to BL by type IV collagen to underlying CT 


proteins of the BL?

type IV collagen 

multiadhesive proteins, laminin 

proteoglycan, perlecan 


these form a meshlike structure


laminin is?

heterotrimeric multiadhesive matrix protein found in all BL 

interacts w/ integrins on 1 end, collagen on other end 

helps integrate structures


most abundant protein in body?



ollagen structure

triple stranded helical conformation, forms a rope-like structure 

can resist tensile forces 

in tendons, are in parallel bundles, aligned along major axis of tendon


proteoglycan structure and function

type of GAG 

hydrate to a high degree, become gel-like to resist compressive forces 

easily form gels


how are collagen in bone, cornea?

arranged in parallel bundles that lie on top of other bundles at right angles 

collagen XVIII is in basal laminae of blood vessels 

Collagen XVIII cleavage -> endostatin, which inhibits angioenesis


what is fibronectin structure, function?

modular protein that binds to other matrix molecules and receptors on cells - binds integrins on 1 end, collagen on other end, integrates binding btwn them


structure, funciton of elastin?

found on skin, blood vessels, lungs 

elastic fibers allow for recoil after transient stretch 

rich in glycine, proline, hydroxyproline 

sheated by microfibrils ocntaining fibrillin


what causes Marfan's syndrome?

mutation in fibrillin I gene 

fibrillin I usually binds to an intert form of TGF-beta, keeps it firmly inactive 

patients w/ fibrillin I mutation means cells cannot form TGF beta in its inactive form, instead get overactive TGF beta and overactivity of the growth factor

leads to defects in tissues rich in elastic fibers, such as aorta, which is prone to rupture; loose joints, weakness in blood vessels, tallness 



what re: fibronectin makes cancer cells more mobile 

cancer cells make less fibronectin -> are more mobile 

are not anchorage dependent 

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