Cell Adhesion Molecules and Junctional Complexes

Question 1

What two components make up the basement membrane? Also, what is each component produced by?

Answer 1

1) Basal Lamina – which is produced by the epithelium.
2) Reticular Lamina – which is produced by connective tissue

Question 2

What components make up the basal lamina?

Answer 2

*Laminin *Fibronectin *Type IV collagen >does not form fibrils like type I collagen >type IV collagen is produced by epithelial cells, unlike type I collagen which is secreted by fibroblasts. *Entactin (nidogen) *Proteoglycans

Question 3

What kind of cells produce type IV collagen, and what type of cells produce type I collagen?

Answer 3

*Type IV – produced by epithelial cells *Type I – produced by fibroblasts

Question 4

Out of all of the components that make up the basal lamina, which component is the major component?

Answer 4

Laminin is the major component of the basal lamina. Laminin consists of three chains: alpha, beta, and gamma, which are disulfide linked polypeptide chains.

Question 5

What binding sites does laminin have that explains the relationship between laminin and the other components that make up the basal lamina?

Answer 5

Has binding sites for integrins, type IV collagen, entactin, and proteoglycans (e.g: heparin sulfate). Thus, make this connection between the components of the basal lamina and the major component of the basal lamina (laminin).

Question 6

Is plasma a form of fibronectin? Also, what cell makes plasma?

Answer 6

Yes, plasma is a form of fibronectin. Plasma is secreted into the bloodstream by hepatocytes.

Question 7

What is fibronectin?

Answer 7

Fibronectin is a protein made up of two polypeptide chains cross-linked by disulfide bonds.

Question 8

What does fibronectin have binding sites for?

Answer 8

*Heparin (proteoglycan) *Integrins *collagen *Fibrin

Question 9

What type of cell produces cellular fibronectin?

Answer 9

Cellular fibronectin is produced by fibroblasts; which is part of the extracellular matrix.

Question 10

Objective 2 Describe the major kinds of cell adhesion molecules (CAMs) and their role in forming cell-to-cell complexes.

Answer 10

Complete

Question 11

Objective 1 Describe the structure and components of the basement membrane.

Answer 11

Complete

Question 12

Which two CAMs are considered calcium dependent and which two are calcium independent?

Answer 12

Calcium Dependent –> Cadherins and Selectins Calcium Independent –> Integrins and Immunoglobulin superfamily molecules

Question 13

What family of CAMs do occludens and desmosomes fall under? Also, is this class calcium dependent?

Answer 13

Cadherins – YES, calcium dependent.

Question 14

What family of CAMs do hemidesmosomes fall into? Is this class calcium dependent?

Answer 14

Integrins and NO, not calcium dependent.

Question 15

What ligands do selectins recognize?

Answer 15

carbohydrates

Question 16

What ligands do the Ig Superfamily recognize?

Answer 16

Integrins

Question 17

Where are E-cadherins, N-cadherins, and P-cadherins found in the body?

Answer 17

E-cadherins –> found in epithelial tissues N-cadherins –> found in nerve cells P-cadherins –> found in the placenta

Question 18

What amino acid sequence does E-cadherins form dimers by?

Answer 18

Histidine-Valine-Alanine (HVA)

Question 19

Calcium ions bind to four extracellular domains and facilitate ______?

Answer 19

cis-homophilic dimers

Question 20

What are catenins?

Answer 20

Small proteins that link the cytoplasmic end of a cadherin with cytoplasmic actin. ***Note that catenins serve as a major interface between the cadherins that hold adjacent cells together and the actin cytoskeletons of those cells***

Question 21

What are the three forms of catenins?

Answer 21

>alpha – binds directly to cytoplasmic actin >beta and gamma – attached to cytoplasmic end of a cadherina, beta may also serve as a transcription cofactor, and beta is also attached to alpha catenin.

Question 22

Selectins are involved in the movement from blood to tissues (extravasation) for which type of cells?

Answer 22

Leukocytes

Question 23

What are the 3 types of listed selectins associated with? *P-selectins *E-selectins L-selectins

Answer 23

E-selectins –> associated with activated endothelial cells P-selectins –> associated with platelets L-selectins –> associated with leukocytes

Question 24

What are integrins? How many subunits make up an integrin?

Answer 24

Integrins are glycoproteins that are mainly involved in cell-extracellular matrix interactions. Each integrin consists of 1 alpha subunit (17 kinds) and 1 beta subunit (8 kinds).

Question 25

Do integrins bind to both the extracellular matrix and the cytoskeleton?

Answer 25

YES, with the extracellular domains binding to molecules such as fibronectin and laminin through an RGD (Arg-Gly-Asp) interaction sequence.

Question 26

Give an example of an intracellular tonofilament that integrins link with to connect the basal domains of cells to the extracellular matrix. Also, in what type of stable junction is this found?

Answer 26

Keratin is the tonofilament and this action is found in the hemidesmosome.

Question 27

True or False: N-CAMs are neural adhesion molecules that mediate only heterophilic interactions?

Answer 27

False –> They mediate both homophilic and heterophilic interactions.

Question 28

What do I-CAM-1 facilitate?

Answer 28

They facilitate transendothelial migration of Leukocytes.

Question 29

Objective 3 Be able to describe the types of junctional complexes and relate them to the cohesive nature of epithelia.

Answer 29

Complete

Question 30

What are the 3 categories of junctional complexes?

Answer 30

*Adherens *Occludens *Gap Junctions

Question 31

What are the 2 main functions of the occluden junctional complexes?

Answer 31

1) to prevent paracellular transport 2) maintain concentration differences

Question 32

What are adherens? Also, what portion of the cell are they found?

Answer 32

Adherens are molecular complexes that anchor cells together and reinforce the physcial integrity of tissues and the cells that make up the tissues.

Adherens can be found on the basolateral surfaces of epithelial cells.

Question 33

What are occludens (tight junctions)?

Answer 33

Occludens are molecular complexes that establish an impermeable barrier between adjacent cells, especially epithelial cells, that prevents paracellular transport and maintains concentration differences between the environments on either side of the epithelial sheets.

Question 34

What are gap junctions?

Answer 34

Gap junctions are composed of molecular pores that enable cells to rapidly exchange ions and small molecules that help coordinate activities among the cells that make up the tissue.

Question 36

True or False:

Zonula Junctions can be either of the adherens or occludens variety?

Answer 36

True

Question 37

True or False:

Macular Junctions can be from either of the adherens or occludens variety.

Answer 37

False, they are of the adherens variety and are often referred to as desmosomes or hemidesmosomes.

Question 38

Between the desmosome and hemidesmosome, which is associated with the lateral domains of epithelial cells and which is associated with the basal domain of epithelial cells?

Answer 38

desmosomes–> associated with the lateral domains of epithelial cells.

hemidesmosomes–> associated with the basal domain of epithelial cells.

Question 39

Between the Zonula or Macula Junction, which one is associated with intracellular actin and which one is associated with intracellular intermediate filaments (tonofilaments)?

Answer 39

Zonula –> associated with intracellular actin

Macula –> associated with intracellular intermediate filaments (tonofilaments)

Question 40

What are the two cadherin proteins that mediate the interaction between zonula adherens with actin microfilaments and macula adherens with intermediate filaments (tonofilaments)?

Answer 40

1) Desmocollins
2) Desmogleins

Question 41

True or False:

The cadherin proteins are anchored to cytoplasmic plaques containing desmoplakin and plakoglobin?

Answer 41

True

Question 42

What is the hemidesmosomes function?

Answer 42

Hemidesmosomes are anchoring junctions that anchor the basal domain of the epithelial cell to the basal lamina.

Question 43

What is pemphigus foliaceus?

Answer 43

Pemphigus foliaceus is an autoantibody-mediated blistering disease in which antibodies against desmoglein 1 cause a loss of adhesion of keratinocytes in the superficial layers of the epidermis.

Question 44

In which layer of the epidermis is the desmoglein 1 predominatly found that is involved in the blistering disease, Pemphigus foliaceus?

Answer 44

Just above the stratum spinosum in the stratum granulosum.

Question 45

True or False:

Occluding junctions (zonula occludens) provide a barrier against the paracellular transport pathway whereby solutes and fluids are transported from one side of an epithelial barrier to the opposite side by passing between the cells?

Answer 45

True