Lecture 19 - Cell Junctions, Adhesion Molecules, and Extracellular Matrix

Question 1

What are the four types of CAM molecules? Which ones are calcium dependent and which aren’t?

Answer 1

Calcium dependent:

• cadherins
• selectins

Calcium independent:

• integrins
• immunoglobulin superfamily

Question 2

What ligands are recognized by each CAM molecule?

Answer 2

Cadherins:
-other cadherins

Selectins:
-carbohydrates

Integrins:
-extracellular matrix molecules

Ig Superfamily:
-integrins

Question 3

What are the different types of cadherins?

Answer 3

Classical cadherins:

• E-cadherin: epithelial tissues
• N-cadherins: nerve and muscle cells
• P-cadherins: placenta and epidermis

Nonclassical cadherins:
-desomcollins and desmogelins (found in desomsomes)

Question 4

What is the difference between homopilic and heterophilic cadherin binding?

Answer 4

Homophilic:

• cadherin molecules which binds to cadherin of the same type (most common)
• uniform spacing

Heterophilic:

• bound cadherin molecules are of different types
• occurs at N-terminals

Question 5

What effect does calcium have on cadherin?

Answer 5

-calcium binds the joints between cadherin domains and prevents flexion

Question 6

Cadherins bind one another with __________ affinity. To counter this, __________ bonds form in parallel resulting in a __________ of cadherin molecules.

Answer 6

Low; many; clusters

Question 7

What is an important function provided by homophilic binding of cadherins?

Answer 7

Sorting out:

• highly selective recognition which allows cells of the same type to recognize one another and stay segregated
• used in cell differentiation in embryo development

Question 8

What molecules bind cadherins to actin filaments?

Answer 8

Catenins:

• β and γ catenins bind cytoplasmic end of cadherin
• α catenin binds β catenin and cytoplasmic actin

Question 9

Loss of which cadherin type is associated with invasive behavior tumors?

Answer 9

E-cadherins

Question 10

What role does calcium play in selectin activity?

Answer 10

-calcium binds near carbohydrate-recognition domain (CRD) and is required for binding to carbohydrates

Question 11

What are the different types of selectins?

Answer 11

P-selectins:
-platelets

E-selectins:
-activated endothelial cells

L-selectins:
-leukocytes

Question 12

Describe the structure and function of integrins.

Answer 12

• proteoglycans
• bind extracellular matrix and cytoskeleton
• consists of α (17 types) and β (8 types) beta subunits
• binds RGD (Arg-Gly-Asp) sequence of extracellular fibronectin and laminin

Question 13

What are the categories of junctional complexes?

Answer 13

Adherens:
-anchor neighboring cells together

Occludens:
-establish impermeable barriers

Gap junctions:
-pores allowing transport between cells

Question 14

What are the types of junctions?

Answer 14

Zonula:

• either adherens or occludens
• present along the entire circumference of a cell linking to all neighboring cells
• associate with actin (using cadherins)

Macula:

• “spot” junctions; desmosomes and hemidesmosomes
• associate with intermediate filaments

Question 15

What are the intercellular anchoring components and the cytoplasmic anchoring components of adherens junctions?

Answer 15

Intercellular:

• desmogleins
• desmocolins

Cytoplasmic plaques:

• desmoplakin
• plakoglobin

Question 16

Desmosomes connect the cell to __________ while hemidesmosomes connect the cell to __________.

Answer 16

Adjacent cells; basal lamina

Question 17

What is pemphigus fallaceus?

Answer 17

• autoimmune blistering disease resulting in the destruction of desmoglein 1 in the upper layers of the epidermis
• allows for formation of fluid pockets in between epidermal layers

Question 18

Describe the structure and function of a zonula occludens.

Answer 18

• “tight junction”
• belt like structure which prevents paracellular transport
• occlusive properties are from claudins and occludens