Junctions

Question 1

Apical surface

Answer 1

increase cell surface

Question 2

lateral surface

Answer 2

cells interact with each other

Question 3

anchoring junctions

Answer 3

interact with cytoskeleton

Question 4

Gap junctions

Answer 4

• connect cyto’s of adjacent cells, ion passage
• integrate individual cells into fxnl unit
• regulated by phosphorylation of connexins and Ca+2
• high Ca+2 closes channel
• communication
• 6 connexins bind= connexon= channel
• cardiac muscle contraction, peristalsis

Question 5

Tight junctions

Answer 5

• b/w PM of adjacent cells
• prevent diffusion of molecules in spaces b/w cells
• prevent diffusion of membrane components b/w apical and basolateral regions of PM
• primarily in epithelial cells
• prevent movement from intestine to blood
• paracellular movement (b/w) cells is prevented
• binding involves occludin, claudin, JAM

Question 6

Cell Adhesion Molecules (CAM’s)

Answer 6

• cadherins, Ig superfamily, integrins, selectins

- cyto domain linked to cytoskeleton via adaptor proteins

Question 7

Homophilic cell-cell adhesion

Answer 7

• interactions b/w same CAM’s of adjacent cells

Question 8

Examples of Homophilic adhesion

Answer 8

• Ig superfamily

- Cadherins

Question 9

Ig superfamily

Answer 9

• mediate Ca+2 independant homocell adhesion

- NCAM, ICAM

Question 10

Cadherins

Answer 10

• Ca+2 dependant
• single transmembrane domain, cyto C-term associated with the cytoskeleton
• essential for holding cells in sheets

Question 11

Cadherin based Anchoring Junctions

Answer 11

• bind membranes of adjacent cells, strength and rigidity
• ADHERINS JUNCTION: connect cadherins to microfilaments through adaptor protiens
• circumferential belt is actin based structure
• DESMOSOMES: connect to intermediate filaments through adaptors

Question 12

Beta-catenin

Answer 12

• beta-catenin functions as a transcriptional activator and as a membrane-cytoskeleton linker protein.

Question 13

ECM functions

Answer 13

• anchoring and engulfing cells to maintian tissue 3d shape
• biomechanical properties (stiffness, rigidity, etc)
• cell polarity, suruval, proliferation, differentiation, fate
• inhibiting/facilitating cell movement
• binding to/acting as a reservoir for growth factors

Question 14

ECM protiens can be

Answer 14

• hydrophilic: proteoglycasn absorb water, tissue resiliency
• strucrutal: collagen
• Adhesive: fibronectin recognized by integrins to allow cell migration

Question 15

Heterophilic interactions

Answer 15

• integrins

- selectins

Question 16

Integrin-Ligand interactions

Answer 16

• can bind fibronectin
• heterodimeric transmembrane protein
• integrins bind core RGD, require synergy regions for specificity
• different Alpha/Beta combinations recognize specific substrates

Question 17

Alpha/beta combinations

Answer 17

• A1B1= collagen
• A5B1 = fibronectin
• A6B1= laminin

Question 18

Integrin connections

Answer 18

• connect cells to ECM
  FOCAL ADHESIONS: cells to ECM (fibronectin) using integrins attached to actin filaments
• Hemidesmosomes: cells to ECM (laminin) using integrins attached to Keratin IF’s
  
  • limited to epithelial cells

Question 19

Integrin’s can…

Answer 19

• be in inactive/active states
• can trasnduce signals
• cellular repsonses to adhesion receptor signalling
• binds ligand= active

Question 20

Selectins

Answer 20

• recognize oligosacchs (glycans)

- participate in leukocyte extravasation

Question 21

Leukocyle extravasation

Answer 21

1. Resting state: absence of inflammation/infection. P-selectin not available
2. Endothelial activtion, attachment, rolling: P-selectin released, binds glycan ligand on leuko. PAF to surface
3. Leuko binds PAF–> activates integrin
4. firm adhesion b/w integrin B2 and ICAM
5. Extravasation