Junctions

Question 1

Integrins

Answer 1

Transmembrane proteins that tie ECM to cytoskeleton.

-bind ligand w low affinity but present in high numbers on cell surface.

Question 2

Integrin Structure

Answer 2

• 2 required non-covalent units (a and B)
• a contributes to binding specificity
• B interacts with cytoskeleton
• requires divalent cations (Mg++ or Mn++)

Question 3

Integrin Function

Answer 3

Binds to ligand, then integrin binds to talin and a-actinin, which initiates complex that link integrin to actin.

• this increases intravellular pH and Ca++ levels, and tyrosine phosphorylation.
• also initiates complex of proteins that regulate and catalyze gene expression, cytoskeleton changes, and adhesion.
• binding anchors cell to matrix at discrete sites called focal adhesions. Stress fibers attach here

Question 4

Focal adhesions

Answer 4

Discrete site where integrin binding anchors cell to matrix

Question 5

Stress fibers

Answer 5

Bundles of actin that attach to focal adhesions

Question 6

Leukocyte adhesion deficiency

Answer 6

Loss of exclusive B2 subunit on white blood cells, no adhesion occurs, patients suffer repeated bacterial infections

Question 7

Glanzmann’s Disease (thrombasthenia)

Answer 7

B3 missing, receptor for fibrinogen doesn’t form, platelets can’t bind to fibrinogen to initiate blood clotting, excessive bleeding occurs.
-treated with platelet transfusion

Question 8

Selectins

Answer 8

Cell surface carb binding proteins. On endothelial and WBCs

Weaker, allows stronger binding to occur (ICAMs) by slowing WBCs

Question 9

E selectins

Answer 9

Secreted by endothelial cells.

• bind oligosaccharides on WBCs
• mediate adhesion between WBCs and endothelial cells

Question 10

P-selectin

Answer 10

Synthesized by platelets

Bind to oligosaccharides on WBCs

Question 11

L-selection

Answer 11

Synthesized by WBCs

Bind to endothelial cells

Question 12

Adherin Junction

Answer 12

Connects Cell to cell via Actin

Caderin-catenin-p120-actin

Question 13

Desmosomes

Answer 13

Connect cell to cell via intermediate filaments

Desmoglein +desmocollin-plakoglobin+plakophillim-desmoplakin-IFs

Question 14

Hemidesmosoms

Answer 14

Connect cell to matrix via intermediate filaments

Laminin-a6b4(integrin)-bp230+plectrum-IFs

Question 15

ICAMs

Answer 15

On endothelial cells, bind integrins on WBC surface strongly, trapping them at inflammation

Question 16

Immune response

Answer 16

Selectins on endothelial cells bind and slow WBCs at specific receptors so integrins on WBCs cam bind to ICAMs strongly

Question 17

Cadherins

Answer 17

Requires Ca2+.

Cell adhesion by homophonic binding, all cells have

Question 18

Cadherin structure

Answer 18

Large extra cellular region.

Cadherin links to p120 and B catenin, which links to A-catenin, which links to actin in cytoskeleton

Question 19

B-catenin, differentiated cells

Answer 19

No Wnt signal. B catenin forms complex, is phosphorylation and degraded.
No binding to Tcf, no transcription

Question 20

B-catenin, undifferentiated cells

Answer 20

Wnt signal present.

Wnt binds to complex. B-catenin doesn’t get touched, goes to nucleus and forms complex w Tcf, transcription activated.

Question 21

APC

Answer 21

If APC protein is defective, B catenin in proliferating cells is not degraded and FAP occurs (colon cancer)

Question 22

Tight junctions

Answer 22

Barrier. Network goes around entire circumference of cell.
Links cells to actin
Occluding/Claudine/JAM-ZO-actin

Question 23

Gap junction

Answer 23

Allows electrical and metabolic coupling of cytoplasm between cells of a single type, can share small molecules

Question 24

Charcot-Marie-Tooth disease

Answer 24

Degeneration of peripheral nerves. Loss of muscle control.

Mutation in connexin 32 gene in Schwann cells that rap around nerves and form myelin