Junctions

Question 1

leukocyte adhesion deficiency

Answer 1

defective integrins

immune cells don’t bind where they should

Question 2

selectins

Answer 2

glycoprotein cell adhesion molecule on leukocytes and activate endothelial cells

Question 3

extravasion

Answer 3

movement of leukocyte towards site of damage

1) WBC circulate freely in blood
2) injury occurs->chemokines released to attract leukocyte
3) WBC begin tumbling process until it finds selectin from which the signal came from
4) WBC binds selectin to endothelial cell, carbohydrate between them
5) this induces a cascade inside WBC to activate integrin-CAM on WBC surface membrane
5) integrin on WBC binds to ICAM (intracellular adhesion molecule) and adheres to endothelial cell

Question 4

cadherin

Answer 4

Ca+ dependent adhesion transmembrane protein
protects extracellular region from degradation
only recognize cadherins on surface of cells from the same species
interacts w/ actin at adheren junctions
needs alpha and beta catenin to work

Question 5

beta catenin

Answer 5

In healthy differentiated cells is degraded outside of cadherin protein:

1) APC and other proteins form a beta catenin destruction complex that phosphorylates beta catenin
2) beta catenin is now primed for ubiquitination
3) ubiquitin tags signal degradation by proteosomes

In undifferentiated cells, or tumor cells, beta catenin can enter the nucleus and act as a transcription factor:

• if Wnt is upregulated it binds to transmembrane protein Frizzled, where the beta catenin destruction complex components are bound, while these components are bound here they cannot bind with APC, and thus the destruction complex is left inactive
• APC gene could also be defective also allowing the destruction complex to remain inactive

Question 6

adenomatous polyposis

Answer 6

genetic disease in which APC gene is defective
causes polyps in epithelium of LI
can lead to cancer, especially colon cancer

Question 7

adhesion belt

Answer 7

connects a bunch of adjacent cells by attaching actin filaments to adheren/cadherin junctions

Question 8

desmosomes

Answer 8

attach cells to each other via cadherin-like proteins and IF
attaches to middle of IF
important in holding cardiac and epithelial cells together

Question 9

desmoglein and desmocollin

Answer 9

cadherin-like prot that extends into ECM and the desmoglein of one cell will match up to the desmocollin of the adjacent cell to form desmosome

Question 10

pemphigus

Answer 10

autoimmune disease against desmosomes

blisters on skin and mucous membranes

Question 11

hemidesmosome

Answer 11

attach cells to the ECM
IF and plectin inside the cell, bind to BSP180 and integrin on the membrane, integrin then binds the ECM outside the cell

Question 12

tight junction

Answer 12

no movement can occur between cells, not even water
important proteins: transmembrane proteins occludin, claudin, and JAM, bind to actin in the cell
blood brain barrier and intestines

Question 13

gap junctions (aka connexons)

Answer 13

channels between cells that only allow fluid and small molecules to pass between cells
can open and shut
things can pass from cell to cell very quickly this way
made of 6 proteins called connexins

Question 14

integrin

Answer 14

a transmembrane protein (cell adhesion molecule CAM) that binds ECM proteins and cytoskeletal proteins
needs both apha and beta subunits to funtion
does not have enzymatic activity, but does manipulate internal cell conditions
doesn’t bind directly to actin, has proteins between: vinculin and talin