2.3: Cell Adhesion

Question 1

cell __________ and __________ is essential for multicelllular organisms

Answer 1

polarization, cohesion

Question 2

polarized cells can? (3)

Answer 2

• define inside vs outside
• have diff functions at diff cell regions
• transmit signals

Question 3

how is mechanical stress transmitted from cell to cell in epithelial tissues

Answer 3

by cytoskeletal filaments anchored to cell-matrix and cell-cell adhesion sites

Question 4

the extracellular matrix directly bears what type of stress (and 2 types of this specific stress)

Answer 4

mechanism: tension and compression

Question 5

what is connective tissue made up of

Answer 5

collagen fibers, ecm, cells kinda spaced far apart

Question 6

many animal cells are either connective or epithelial tissue, what are these?

Answer 6

epithelial tissue: cells directly connected to each other w minimal ecm (basal lamina sometimes considered part of epithelial tissue)
connective tissue: cells dispersed through ecm

Question 7

state what epithelial cells line and provide examples

Answer 7

surfaces: protective epithelial cell layers on the surface of the organism (skin)
cavities: absorptive epithelial cells lining a cavity of the organism (digestive tract)
organs: epithelial cells surrounding and defining organs

Question 8

t/f are lining patterns consistent

Answer 8

true

Question 9

t/f are epithelial cells polarized and explain how

Answer 9

true. each cell surface must be different to perform different functions, these cell surfaces define the inside vs outside of the organism or tissue

Question 10

list the junctional complexes of (mature) epithelial tissues from apical to basal

Answer 10

tight junction, cell-cell anchoring junction, channel forming junction, cell-matrix anchoring junctions

Question 11

define tight junctions

Answer 11

seals gap between epithelial seals. all along the region between two cells, makes sealing strands

Question 12

the order of junctional complexes from apical to basal are distinct, are these the same in all cells

Answer 12

• mature cells definitely have junctions and in that order
• other cells may or may not have all of them or in that order (case to case dependent)

Question 13

what makes sealing strands and what makes adhesion belts

Answer 13

tight junctions make sealing strands and adherens junctions make adhesion belts

Question 14

define adherens junction

Answer 14

connects actin filament bundle (apart of cytoskeletal filaments) in one cell with that in the next cell. the actin anchors on that side of the cell and doesn’t go to other side, the adherens junction is all along region between two cells to form adhesion belts

Question 15

define desmosome

Answer 15

desmosomes connects intermediate filaments (cytoskeletal filaments) in one cell to those in the next. desmosomes are just in that spot and don’t go to the other side.

Question 16

define gap junctions

Answer 16

allows the passage of small water-soluble molecules from cell to cell (not with outside cell)

Question 17

what does relative positioning mean in epithelial cells

Answer 17

it’s when there is greater presence of a junctional complex on the apical vs basal side - eg desmosomes more apical than gap junctions

Question 18

what (2) types of junctional complexes connect the epithelial cell of the basal connective tissue underneath

Answer 18

1. actin linked cell matrix junction: anchors actin filaments in cell to ecm
2. hemidesmosome anchors intermediate filmaments in cell to ecm
   note that filaments don’t go outside (cytoSKELETAL stays inside)

Question 19

which junctional complexes are considered cell cell junctions

Answer 19

adherens and desmosomes

Question 20

which junctional complexes are considered cell-ecm junctions

Answer 20

actin linked cell matrix junction and hemidesmosomes

Question 21

cell cell junctions are usually mediated by ____________ and cell-ecm junctions usually mediated by ___________ and cytoskeleton may be _______ or ____________ filaments

Answer 21

cadherins. integrins, actin or intermediate filaments
*cadherins is for adherin junctions and cadherin family is for desmosomes

Question 22

what are intracellular adaptor proteins used for

Answer 22

they are inside the cell and they hold the transmembrane adhesion proteins while the other end of the tm prot either is cell-cell or cell-ecm

Question 23

cadherins are tm proteins expressed by (one or both) cells - cadherins mediate cell-cell connections at adherens junctions

Answer 23

both (it’s like velcro)

Question 24

cadherins interact (homophilic or heterophilic) interactions of their extracellular domains

Answer 24

homophilic - N terms of both connect
ie e cadherin can go w e cadherin but cannot go with n cadherin

Question 25

cadherins interactions require what and what does it do

Answer 25

ca2+ - makes hinge regions rigid to help them stick together (think of wrists as the hinge in regards to arm)

Question 26

what is the result of homophilic cadherin interactions

Answer 26

cells expressing different cadherins sort into two separate groups that do not interact

Question 27

cadherins form homophilic interactions with their ec domains to directly link _____________ and indirectly interact with __________-_

Answer 27

adjacent cells, actin filaments

Question 28

do cahrerins act directly or indirectly with actin filaments, and what is the result

Answer 28

indirectly ==> these interactions indirectly link the actin cytoskeleton between adjacent cells in epithelial tissues

Question 29

caherins interact in patches to form a strong _________ belt

Answer 29

adhesion

Question 30

adhesion belts can mediate ?

Answer 30

morphogensis

Question 31

describe morphogenesis by adhesion belts

Answer 31

the sheet of epithelial cells can undergo invagination caused by an organized tightening of adhesion belts in selected regions of the cell sheets (the actin contracts = tightening = shape forming) -> epithelial tube pinches off from overlying sheets of cells -> then it can become a shape eg the epithelial tube

Question 32

t/f you need the correct cadherins to create specific shapes through morphogenesis

Answer 32

true

Question 33

in an ectoderm, cells express different cadherins to establish new interactions and ensure the closure of which feature

Answer 33

neural tube closure (the neuron tube is joined by a different cadherin that made up the original ectoderm and the original cadherin that makes up the neural tube)

Question 34

cell adhesion is essential for which 2 processes

Answer 34

embryo development (must adhere properly so when the cells move itll be coordinated movements to separate head from a foot yk) and morphogenesis

Question 35

Which of the following most closely resembles adherens junctions mutations in the outer epithelium of Drosophila embryos? a) Hemidesmosome mutation in the outer epithelium. b) Calcium removal at the outer epithelium. c) Intermediate filament depolymerization in the outer epithelium. d) Occludin mutation in the outer epithelium.

Answer 35

B. A is wrong bc if doesn't resemble. B is right be we need calcium to make it rigid so no calcium will make it flimsy thus the embryo won't develop properly. C is wrong bc it's not intermediate filaments, I think it's actin (double check). D is wrong bc occludin is for tight junctions.

Question 36

tight junction define the _____ of the cell

Answer 36

domains - they separate apical and basal

Question 37

state what the apical and basal domain face

Answer 37

apical - surface, cavity, organ basal - inside of the body

Question 38

occludins and claudins form ___________ and these form ________ strands

Answer 38

tight junctions == sealing strands * many rows of these proteins are needed to form a functional tight junction

Question 39

claudin and occludin are tight junction proteins with how many passes into the TM

Answer 39

4

Question 40

occludins and claudins for homo or heterophilic interactions with their ec domains to directly link adjacent cells

Answer 40

homophilic

Question 41

is linking of adjacent cells by tight junctions direct or indirect

Answer 41

direct

Question 42

tight junctions limit diffusion into the __________ space and limit the diffusion of what

Answer 42

extracellular, membrane proteins

Question 43

membrane proteins can or cannot diffuse in the plasma membrane

Answer 43

can

Question 44

which junctional complex prevent membrane proteins from moving between the apical and the basolateral domains

Answer 44

tight junctions

Question 45

explain how tight junctions regulate what enters an organism (in the example of absorbance of glucose from the intestinal lumen)

Answer 45

- tight junctions function to stop anything from directly diffusing from the gut lumen into connective tissue and blood - active transporters (Na+ driven glucose transporter) must move glucose into the epithelial cell on the apical domain from the gut lumen (low C gluc bc keeps being moved into cell) - passive carriers (passive glucose transporter) in the basolateral domain allow glucose to diffuse out of the epithelial cell into the connective tissue/blood - tight junctions keep the correct transporters in their correct domains of the cell

Question 46

in the absorbance of glucose from the intestinal lumen, state the 2 relevant transporters and which domain they are in

Answer 46

na+-driven glucose transporter (active) in the apical passive glucose transporter (passive) in basolateral

Question 47

_______________ mediate cell to cell matrix junctions

Answer 47

integrin heterodimers

Question 48

integrins directly or indirectly interact w actin filaments

Answer 48

indirectly

Question 49

cell matrix junctions play roles in both epithelial and connective tissues, define these both

Answer 49

epithelial tissue: adhesion to the basal lamina ecm connective tissue: cell interaction iwth the ecm and cell movement

Question 50

what are polarity cues

Answer 50

signal to make ends different, these can establish cell cohesion

Question 51

what is cell cohesion established by

Answer 51

polarity cues

Question 52

describe how polarity cues can establish cell cohesion and examples

Answer 52

- adherens junctions form first, this is the primary landmark --> subsequent elaboration - adherens junctions provide polarity cues to define apical from basolateral domains for epithelial cells (the first polarity cue defines the rest) - tight junctions form apical to the adherens junctions-after the separation of apical and basolateral example: adherens junction cause the polarity cues of par and crumbs to dictate the apical domain. it inhibits scribble (polarity cue) which creates the basolateral domain

Question 53

t/f only epithelial cells use the polarity cue systems

Answer 53

no, all cells

Question 54

state what an initial landmark (can be strucutre, prot, signal, or process) generate

Answer 54

subsequent patterns

Question 55

describe how ec signals can polarize cell behaviour in regards to rac and rho

Answer 55

on neutrophils, the chemoattractant acts on the receptor which is the primary landmark that indicates rac (polymerization (- protrusion)) to go towards and rho to go away (actin-myosin contraction)

Question 56

t/f cell polarity can be established external OR internal signals

Answer 56

true

Question 57

describe how external signal (sperm entry) can establish cell polarity

Answer 57

the initial polarity signal was external (sperm entry) which is the primary landmark. asymmetric cell division can unevenly distribute internal polarity cues between child cells -- defining the anterior and posterior through the rho gef gradient.

Question 58

An occludin mutation in ________ cells will directly affect __________. a) intestinal epithelial; glucose transport. b) Drosophila embryonic; movement of the outer epithelium. c) Drosophila embryonic; segmentation of the outer epithelium. d) epithelial; adherens junction formation.

Answer 58

A. B is wrong bc movement is for cadherin. C is wrong bc we don't even know segmentation. D is wrong bc if adherens it's a whole separate thing and they form before tight junctions

Question 59

list the 3 key components of cell polarity to define a functional epithelium

Answer 59

intracellular trafficking, cytoskeleton organization, cell cohesion

Question 60

what does a functional epithelium define

Answer 60

organs and organisms by separating proteins on sides and keeping them there