Lecture 12 - Adhesion

Question 1

2 methods for cells to interact with each other and recieve/send signals

Answer 1

1. physically touching each other
2. sending diffusible signals to each other

Question 2

How do cells stick to each other/surfaces in the lab

Answer 2

• they have CAMS embedded in the trans membrane
• part of the CAM sticks in the cytoplasm and other part outside the cell which is long
• 2 cells that are close together are able to reach out and touch each other’s cams to send info

Question 3

What info do CAMS send

Answer 3

• that they are next to a cell and should or should not adhere

Question 4

What is the extracellular matrix?

Answer 4

A network of proteins outside cells that provides structural support and signaling
gets information from the matrix

Question 5

2 functions of the extracellular matrix

Answer 5

1. allow cells to attach (adhesion)
2. provides signals that influence cell behaviour

Question 6

What info does the extracellular matrix give to cells?

Answer 6

signals about adhesion, movement, growth and differentiation

cells communicate with each other via extracellular matrix

Question 7

What is the basolateral extracellular matrix in epithelial cells

Answer 7

anchors cells and provides polarity cues (basement membrane)

Question 8

CAMs diversity

Answer 8

• homologous but diversified to form different function that they can do in different cells

Question 9

Types of CAMS

Answer 9

• cadherins
• immunoglobin
• integrins
• lectins (selectins)

Question 10

Cadherins

Answer 10

• calcium dependent to adhere cells together and link
• homotypic (extracellular domain binds to extracellular domain of a similar cell) - bind to identical cadherin molecules on adjacent cells
• weak interactions but allows cells to alter adhesion by deciding how many cadherins are present on the surface
• cadherins find each other
• interact with cytoskeleton via catenins and bind to actin via catenin

Question 11

How to increase adhesion with cadherins

Answer 11

More cadherins = more homotypic/heterotypic interactions = more adhesion = more sticky

Question 12

Why are cadherins binding to actin important?

Answer 12

allows cells to move around, they send signals back to the cell that they are sticking to something and causes the cells to adhere even more closely (reshape themselves to maximize adherence)

Question 13

What 3 polymers are the cytoskeleton made out of?

Answer 13

1. microfilaments
2. microtubules
3. intermediate filaments

Question 14

Integrins

Answer 14

• bind to extracellular matrix proteins, binds to laminin
• proteins in the cell membrane that stick out of the cell and connect inside the cell

Question 15

clusters of cells

Answer 15

If you mix 2 clusters of cells together, they recognize each other and only adhere to their own species to make 2 different unmixed species

Question 16

Structure of extracellular matrix

Answer 16

• Triple helix collagen with laminin

Question 17

How does collagen form outside the cell?

Answer 17

1. made in the ER
2. 3 collagens wind around each other to form procollagen with globular domains
   - this forms a triple helix
3. moves to golgi
4. some propeptides (ends) get removed which get deposited outside the cell and discarded
   - this converts procollagen –> collagen
5. they can self assemble into larger collagen fibres that forms the extracellular matrix

Question 18

Collagen I vs collagen IV

Answer 18

most collagens like type I form fibers

Collagen IV forms a network (mesh/net) which is found in basement membranes

Question 19

How does collagen IV form a network

Answer 19

• has globular domains at its end which allows molecules to connect in multiple directions

Question 20

the c and n terminus of networks/mesh

Answer 20

• the c terminal ends of 2 collagen molecules bind to form a dimer
• the N terminal ends can bind 4 collagen molecules together forming a tetramer of triple helices (node)

the nodes + dimers connect across space and form a network

Question 21

What does the network do?

Answer 21

• attract other extracellular matrix components
• decorate them (adding more information to the matrix)

Question 22

Why is vitamin C necessary in diet

Answer 22

it is a necessary cofactor for an enzyme that hydroxylates collagen propeptides and makes collagen stable

without vitamin c - weak hydrogen bonding and triple helix is unstable so low annealing temperature and the collagen falls apart very easily

Question 23

Effects of scurvy on the body

Answer 23

• weak connective tissue
• bleeding gums
• poor wound healing
• fragile skin/blood vessels

Question 24

Laminan

Answer 24

• protein in the extracellular matrix with n and c terminal globular domains
• especially important in the basement membrane

Question 25

what can laminin bind to

Answer 25

1. other laminins (stick to each other and form network) 2. Collagen IV network (links different parts of the extracellular matrix together) 3. Cell membrane - laminins bind to integrins

Question 26

How do cells control laminin binding

Answer 26

talin controls integrins --> integrins control laminin talin is found inside the cell and when it binds to integrin the integrin can grab to laminin strongly and cells can stick to extracellular matrix

Question 27

what are desmosomes and why do they exist

Answer 27

adhesive protein complexes which hold cells together so tissues dont tear by connecting intermediate filaments they exist because binding via membrane proteins is not strong enough

Question 28

how do desmosomes work?

Answer 28

- inside the cell there are intermediate filaments - these attach to adaptor proteins - which connects it to the membrane proteins that sit in the cell membrane and stick out of the cell - so they can grab the same proteins from the other cell - membrane protein connects to adaptor proteins and intermediate filaments makes tissues strong - spreads force

Question 29

compromised desmosomes

Answer 29

- no strong attachment between cells - people get blisters easily on their skin because their skin loses integrity

Question 30

what are focal adhesions made out of?

Answer 30

- integrins which grab the outside - proteins inside connect like this Extracellular matrix --> integrins --> proteins ---> actin

Question 31

How a cell moves

Answer 31

1. cell forms a new focal adhesion at the front 2. integrins bind to laminin (ECM) or surface 3. actin pulls the cell toward the new attachment 4. old focal adhesions at the back release

Question 32

RS between laminin and integrins

Answer 32

Laminin is outside the cell Integrins are in the membrane (trans membrane) integrins bind laminin to attach the cell to the ECM inside of integrins connect to actin outside of integrins bind to laminin

Question 33

role of laminin

Answer 33

the 'platform' cells attach to bridge, not active

Question 34

talin control

Answer 34

talin activates integrins and so in turn make integrins bind laminin more strongly