Cell Adhesion and Communication

Question 1

what is epithelial tissue?

Answer 1

covers the surface of internal and external organs

- layers of cells on top of a basement membrane

Question 2

how do layers of epithelial interact?

Answer 2

the cells adhere laterally and to the basement membrane via cell matrix interactions

Question 3

how can connections between cells be established?

Answer 3

tight junctions
adherens junctions
desmosomes
gap junctions
non-junctional adhesions

Question 4

what is meant by tight?

Answer 4

impermeable to most molecules and is found in between epithelial cells

Question 5

what is meant by attachment?

Answer 5

actin and intermediate filaments on adjacent cell, sticks cells to the ECM

Question 6

what is mean by comminication?

Answer 6

connects the cytoplasm between adjacent cells

Question 7

how can connections between cells and their underlying matrix be established?

Answer 7

hemidesmosomes

focal adhesions

Question 8

what are the features of tight junctions?

Answer 8

• bands of interconnected strands of integral membrane protein encircling the cell
• as a complex they wrap around adjacent cells

Question 9

what are sealing strands in tight junctions?

Answer 9

• contain 3 transmembrnae proteins: claudins, occludins and JAMs.
• proteins in the sealing strands attach to stably structural proteins
• and transiently to signalling proteins

Question 10

what proteins are the core of tight junction fibirls?

Answer 10

claudins

Question 11

what do tight juncctions do?

Answer 11

form a tight barrier between epithelial cells

- not completely impermeable allows ions, solutes and some electrical currents

Question 12

how do tight junctions differ?

Answer 12

• different tight junctions allow different electric currents (vary in size and charge)
• selectively from different claudins, how the different claudins arrange the loop

Question 13

how do claudins interact with claudins from adjacent cell?

Answer 13

arrange to form a pore

Question 14

what do occludins and JAMs do?

Answer 14

they stabilise (not structural)

Question 15

where is an example of claudin specificity?

Answer 15

kidney (example):

• Claudin 16  restricted to the ascending limb
• Mg+ and Ca2+ not able to pass through the epithelial cells

Question 16

what is paracellular transport?

Answer 16

• Transport of substances across all epithelium by passing through the intracellular space between the cells
• Regulated by claudins
• Act as molecular sieves

Question 17

what is transcellular transport?

Answer 17

• Transfer by passing through cells cross both the apical and basolateral membranes
• Allows the transport of substances against their concentration gradient

Question 18

use glucose as an example of transcellular transport?

Answer 18

• Example: absorption of glucose
   Across intestinal epithelium
   If we relied on diffusion it could only do this until equilibrium is reach
   ATPase and the GLUT2 in basolateral (not in the apical) ATP to sodium ions out of the cell = low concentration then Na+ flows into the cells and carries the glucose in
   Also important that the sodium/glucose symporter is in the apical not the basolateral
   Glucose flows down its concentration gradient into the bloodstream
   Only works if you have certain proteins on certain sides of the membrane
   Apical and basolateral membranes maintain unique identity.

Question 19

what make up attachment junctions?

Answer 19

adherens junctions and desmosomes

- they are bridged by rod like structures

Question 20

how to adherens junction connect to adjacent cells?

Answer 20

• bridge to connect the actin cytoskeletons
• link to actin filaments through catenins
• the presence of cadherins that bind identical cadherins from neighbouring cells

Question 21

what are cadherins?

Answer 21

transmembrane proteins

Question 22

where do adherens junction have an important role?

Answer 22

in tissue organisation

Question 23

what determines how tightly adherens junctions stick together?

Answer 23

the number and type of cadherins

Question 24

how to adherens junctions all link to the actin cytoskeleton?

Answer 24

• regulate changes in cell shape in response to sheer stress

- zonular adhesions

Question 25

what are zonular adhesions?

Answer 25

- cadherins - role in signalling - when disrupted they can enter the nucleus as a transcription factor

Question 26

what is the role of desmosomes?

Answer 26

add structural integrity, link intermediate filaments together through adaptor proteins

Question 27

what is the structure of desmosomes?

Answer 27

contains cadherins as well as desmocollins and desmogleins (stabilising proteins) can be called spot desmosomes as they stick together

Question 28

what is the function of desmosomes?

Answer 28

- linked by stabilising proteins - linked to intermediate filaments through adaptor proteins - bridge the intracellular space and serve as docking sites for cystolic proteins

Question 29

what are hemidesmosomes?

Answer 29

form attachment junctions to connect cell to the underlying matrix

Question 30

where are hemidesmosomes?

Answer 30

located exclusively on the basal membrane

Question 31

what is the structure of hemidesmosomes?

Answer 31

- have cytoplasmic plaques composed of integrin and that adaptor protein plectin

Question 32

what is the function of hemidesmosomes?

Answer 32

- provide structural stability to the epithelial sheet | - anchor cells to basemembrane through cytoplasmic plaques that connect to intermediate filaments

Question 33

how do hemidesmosomes and desmisomes work together?

Answer 33

for structural integrity, allow intermediate filaments to form a network throughout the cell

Question 34

what are focal adhesions?

Answer 34

integrins link to the actin cytoskeleton to the babsement membrane

Question 35

what are integrins?

Answer 35

heterodimers of alpha and beta subunits (18 alpha subunits and 8 beta subunits) - 24 different integrin heterodimers known

Question 36

how do integrins associate?

Answer 36

non-covalently

Question 37

what do integrins bind to?

Answer 37

extracellular matric (ECM) components

Question 38

what is integrin specificity determined by?

Answer 38

composition of heterodimers - common beta subunit - variation in alpha subunit contributes to specificity

Question 39

what determines which ECM a cell can bind?

Answer 39

- different integrins - different cell types express different integrins - different ECM have different composition - expression profile can change during development

Question 40

what can binding of integrins to ECM be altered by?

Answer 40

environment

Question 41

what do all known binding sites on ECM proteins contain?

Answer 41

- an amino acid often aspartate | - many contain the sequence Arg-Gly-Asp

Question 42

what is inside out signalling?

Answer 42

-  Activates talin and induces dimerization |  Talin binds to β integrin subunit causing a conformational change in the integrin extracellular domain  an example

Question 43

what is outside in signalling?

Answer 43

 Transduce information outside to inside  When a cell binds to ECM it can cluster integrin’s forming a docking site for signalling molecules that then bring about changes inside the cell

Question 44

how can integrins regulate cell movement?

Answer 44

- induce actin remodelling | - through intracellular trafficking

Question 45

how can integrins regulate cell movement through intracellular trafficking?

Answer 45

- endocytosis of integrins can be used to break attachment of a substrate - allows a focal adhesion to move on - traffics into a compartment into an endosome

Question 46

what happens when trafficking is disrupted?

Answer 46

- mistargeted to lysosome | - common in some cancers as you lose attachment

Question 47

where else are integrins importnat?

Answer 47

non-junctional cell adhesions

Question 48

what are gap junctions?

Answer 48

- communication junctions - allows the direct transfer of ions/small molecules between adjacent cells - found in most vertebrae and invertebrae - only known means of cell to cell transport - also facilitates electrical signals between cells

Question 49

how can you spot a gap junction?

Answer 49

plasma membranes appear clustered together in the surround area with gaps bridge by channels projecting out of the plasma membrane

Question 50

what are connexions?

Answer 50

- proteins in gap channel

Question 51

what is the structure of connexions?

Answer 51

- have 4 transmembrane domains - 6 of these make up a conexxion - 2 connexons on adjacent cells form a channel

Question 52

what is the function of connexions?

Answer 52

- transport small molecules - ions sugars amino acids nucleotides - electrically couples neighboring cells - have different permeability properties depending on connexions present

Question 53

what are the functions of gap junctions?

Answer 53

- when you need rapid communication, eg reflex reactions

Question 54

what are mutations in gap junctions linked to?

Answer 54

heart disease

Question 55

how are gap junctions regulated?

Answer 55

alternate between open and closed states - large increases in intracellular calcium ion concentration and/or pH induce gap junction closure - gap junction closure prevents further damage to neighouring cells