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

Question 1

what is epithelia

Answer 1

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

Question 2

are epithalial cells polarized

Answer 2

yes

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

Question 3

kinds of cells in body

Answer 3

epithelia

connective tissue

muscle cells

nervous cells

blood cells

Question 4

ell adhesion moecules

Answer 4

1) cadherins
2) IG superfamily
3) integrins
4) selectins

Question 5

homophilic vs heterophilic binding

Answer 5

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

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

Question 6

cell adhesion molecule functions inside cells

Answer 6

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

Question 7

ECM functions

Answer 7

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

Question 8

what comprises ECM?

Answer 8

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

Question 9

purpose of epithelial cells’ polarized cellular organization

Answer 9

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

Question 10

what is on apical surface of epithelial cells

Answer 10

villi

for absorption

Question 11

cell junctions in epithelial cells

Answer 11

1) tight junctions
2) anchoring junctions: adherens, desmosomes, hemidesmosomes
3) communicating junctions: gap junctions
4) integrins

Question 12

tight junctions function? structure?

Answer 12

exist directly under microvilli

seal epithelial cells together in sheets

prevents passage of small molecules

Question 13

tight junctions made of?

Answer 13

claudins, occludins

Question 14

anchoring junctions function

Answer 14

join cells to each other and to ECCM

1) adherens junctions and desmosomes
2) focal adhesions and hemidesmosomes

Question 15

adherens junctions and desmosomes functions

Answer 15

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

Question 16

nature of caderins throughout the body?

Answer 16

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

Question 17

focal adhesions?

Answer 17

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

Question 18

desmosomes connect with what?

Answer 18

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

Question 19

hemidesmosomes are made of?

Answer 19

IF

bind inside the cell, and to the ECM via integrin

Question 20

gap junctions function?

Answer 20

cell - cell communication

allwo for electrical coupling between cells

Question 21

what are cadherins

what does their loss result in

Answer 21

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

Question 22

integrins function

Answer 22

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

Question 23

what integrain is a hemidesmosome connection

Answer 23

a6b4 interacts w/ IFs a hemidesmosomes

exception to integrins connecting to bundled actin filaments

Question 24

what mediates actin-integrin interaction

Answer 24

anchor proteins - talin, a-actinin, filamin

linkage leads to clustering and formaiton of focal adhesions

Question 25

what are selectins?

Answer 25

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

Question 26

how do WBC travel around the blood

Answer 26

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

Question 27

what is ECM

Answer 27

space between cells a misture of proteins and polysaccharides high ECM in bone and cartilage, low ECM in brain and spinal cord

Question 28

what forms bone/teeth

Answer 28

calcified ECM

Question 29

how is ECM in tendon

Answer 29

trannsparent

Question 30

what is basal lamina

Answer 30

form of the ECM at interface of epithelia and connective tissues

Question 31

where is basal lamina found

Answer 31

underlies epithelial cell sheets and tubes around muscle cells, fat cells, schwann cells separates these cells from CT and serves as highly selective filter

Question 32

what does basal lamina influence

Answer 32

cell polarity, metabolism, survival, proliferation, idfferentiation serves as highway for migration

Question 33

what forms BL

Answer 33

cells that sit on it

Question 34

what is basement membrane

Answer 34

structure connected to BL by type IV collagen to underlying CT

Question 35

proteins of the BL?

Answer 35

type IV collagen multiadhesive proteins, laminin proteoglycan, perlecan nidogen these form a **meshlike structure**

Question 36

laminin is?

Answer 36

heterotrimeric multiadhesive matrix protein found in all BL interacts w/ integrins on 1 end, collagen on other end helps integrate structures

Question 37

most abundant protein in body?

Answer 37

collagen

Question 38

ollagen structure

Answer 38

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

Question 39

proteoglycan structure and function

Answer 39

type of GAG hydrate to a high degree, become gel-like to resist compressive forces easily form gels

Question 40

how are collagen in bone, cornea?

Answer 40

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

Question 41

what is fibronectin structure, function?

Answer 41

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

Question 42

structure, funciton of elastin?

Answer 42

found on skin, blood vessels, lungs elastic fibers allow for recoil after transient stretch rich in glycine, proline, hydroxyproline sheated by microfibrils ocntaining fibrillin

Question 43

what causes Marfan's syndrome?

Answer 43

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

Question 44

what re: fibronectin makes cancer cells more mobile

Answer 44

cancer cells make less fibronectin -\> are more mobile are not anchorage dependent