Week 7: Cell cell jxns

Question 1

cell junctions

Answer 1

structurally and functionally diverse which can be classified into several groups

Question 2

anchoring junction

Answer 2

mediate cell/cell and cell/matrix interactions as the contact between cells
- adherens junctions
- desmosomes
- hemidesmosomes

Question 3

adherens junction

Answer 3

connects actin filament bundles in one cell with another cell via cadherins

Question 4

desmosomes

Answer 4

connects intermediate filaments in one cell to those in the next cell via cadherins

Question 5

hemidesmosomes

Answer 5

anchors intermediate filaments in cell to extracellular matrix via integral and collagen types

Question 6

occluding junctions

Answer 6

seal the gaps between epithelial cells
- tight junctions

Question 7

tight junction

Answer 7

seals the gap between epithelial cells

Question 8

channel forming junctions

Answer 8

form passageways between neighboring cells
- gap junctions

Question 9

gap junction

Answer 9

allows the passage of small water-soluble molecules from cell to cell

Question 10

which side is the extracellular matrix on? Basal or Apical

Answer 10

basal lamina side

Question 11

intracellular adaptor proteins

Answer 11

proteins on the inside of the cell that either link to another transmembrane protein between the two cells or between the cell and the ECM

Question 12

transmembrane adhesion proteins

Answer 12

proteins that directly link either two cells or link the cell to the extracellular matrix
- they are all transmembrane proteins

Question 13

cytoskeletal filaments

Answer 13

intracellular domains of transmembrane adhesion proteins get lined with this

Question 14

actin linked cell matrix junction

Answer 14

anchors actin filaments in a cell to extracellular matrix via integrin

Question 15

cadherin vs integrin

Answer 15

cadherin forms cell to cell junctions via actin or intermediate filaments while integral forms cell to matrix junctions via actin or intermediate filaments

Question 16

Chelated

Answer 16

something that will bind the calcium ions and remove it from an organism
- happens with EDTA

Question 17

Ca2+ dependent

Answer 17

non functional when Ca2+ is chelated
- cadherin domains are mediated by Ca2+

Question 18

what 2 things does Ca2+ mediate?

Answer 18

1. homophilic adhesion (the same cadherin molecules bind to itself (E to E and N to N)
2. selective cell sorting where the same groups of cells expressing certain amounts of cadherins will bind to themselves (high cell expression goes to the middle clump)

Question 19

anchoring junction and cadherins

Answer 19

cadherins form clusters and accumulate many weak bonds which form a strong junction like a velcro effect

Question 20

aggregates

Answer 20

mixtures of cells expressing two different cadherins will sort into individual clumps
-E cad vs N cad clumps

Question 20

how are cadherins involved in animal cell sorting?

Answer 20

amphibian embryos were dissociated into single cells and the cells were mixed so they could re-associate. The cells reassembled into structures like the original embryo
- neural plate cells on the inside, mesoderm cells in the middle, and epidermal cells on the outer layer
- the same cell types associated together in aggregates

Question 21

what happens when cells have different levels of promotor expression of the same cadherin?

Answer 21

the two cell types will express different levels and aggregate with the high expression E cells in the middle and lower expression E cadherin cells on the outside

Question 22

what 2 things explain cell aggregates?

Answer 22

1. types of cadherin
2. expression of cadherin

Question 23

adaptor proteins

Answer 23

these link to the intracellular domain of the cadherin and then also link to actin filaments
- this forms the complex for cell-cell adhesion
- form of indirect binding between cadherins and actin filaments

Question 24

types of adaptor proteins from class (4)

Answer 24

- p120 catenin linking directly to cadherin - beta cetenin which also links directly yo cadherin - alpha catenin which links to beta catenin and some actin filaments - vinculin which links to alpha catenin and actin filaments

Question 25

how does cortical tension aid formation of adherens junctions?

Answer 25

small cadherin clusters send a message to the cellular cortex and tell actin to dissociate, the cadherins signal to inhibit Rho and activate Rac which disassembles actin myosin fibers and loses cortical tension, recruitment of more cadherins helps the spread of the cell to cell junction - Rho and Rac are GTPases involved in actin myosin assembly

Question 26

continuous adhesion belt

Answer 26

in epithelial cells, adherent junctions are connected as homophilic and calcium dependent binding that interact with adaptors and actin filaments - the actin filament goes to the other side of the cell and connected to the junctions on the other side of the cell as well which makes it continuous

Question 27

invagination of actin

Answer 27

this contraction of the network provides the force required to fold epithelial sheets during development - the adhesion belt is organized to tighten in certain regions of the cell

Question 28

tube formation

Answer 28

invagination of the epithelial cells will pinch off to form a tube underneath the overlying sheet of epithelial cells - the basal side is together while the other side is not and the apical side can be contracted to be more narrow

Question 29

desmosomes and cadherins

Answer 29

clusters of cadherins form plaques that link the intermediate filament and use similar structure as adherent junctions but different types of cadherins - nonclassical cadherin proteins

Question 30

what are the cadherin types (2) used in desmosomes?

Answer 30

desmoglein and desmocollin

Question 31

what are the adaptor proteins used in desmosomes?

Answer 31

1. plakophilin binds directly do cadherin 2. plakoglobin binds to cadherin and plakophilin and desmoplakin 3. desmoplakin binds to plakoglobin and the intermediate filaments

Question 32

what is the structural framework function desmosomes provide?

Answer 32

they provide mechanical strength (often the intermediate filament is keratin)

Question 33

how do tight junctions organize epithelial cells?

Answer 33

with the apical side of occludin junction they connect each cell and strictly seal them together - this prevents glucose from leaking back into the gut lumen instead of moving toward the blood

Question 34

basal lamina (basement membrane)

Answer 34

thin membrane sheet sealed together by tight junctions such as in the gut epithelium

Question 35

describe glucose trancellular transport

Answer 35

1. Na+ driven glucose transporter are on the apical membrane and uptake glucose into the cell 2. passive glucose transporters are on the basolateral membrane and exposed glucose goes to the basal side where it is passed to the basal lamina and into the blood with the ECM fluid and connective tissue

Question 36

functions of tight junctions

Answer 36

1. Diffusion barrier: transported molecules cannot leak back 2. Fences: within the membrane are apical (BL) transmembrane proteins that cannot diffuse into the other side

Question 37

what 2 proteins compose tight junctions?

Answer 37

adhesion transmembrane proteins Claudin and occludin (intercellular space) - the two cells match together so that small molecules cannot pass between them

Question 38

intercellular space

Answer 38

between cells which becomes occluding in the area of the tight junction - the plasma membranes are brought into close proximity

Question 39

how do gap junctions work?

Answer 39

they form cell to cell channels and allow small molecules 1,000 daltons or less into neighboring cells - this couples the cells electrically and metabolically

Question 40

what proteins form the gap junction?

Answer 40

connexon proteins which involve 6 transmembrane connexin proteins assembled into a hemichannel to form the aqueous channel connecting the cytosol of the cells - they may be homomeric or heteromeric

Question 41

homomeric vs heteromeric

Answer 41

connexons of all identical molecules vs connexions that have some different molecules - forms homotypic (all 1 molecule) and heterotypic which may have different molecules anywhere in the connexion

Question 42

what functions do gap junctions have? (2)

Answer 42

1. action potentials in nerve cells where pulses spread rapidly from one cell to another 2. coordinated cell responses in cells that are not electrically excitable