Junctions

Question 1

Describe the structure of Integrin and the purpose for each subunit

Answer 1

Integrins are made up of a- and B-subunits that are not covalently bound. The a-subunit is used for ligand recogniztion primarily
B-unit is used to connect to the cytoskeleton
Binding requires divalent cations (Mg or Mn)

Question 2

What does an Integrin bind to within the cell?

Answer 2

Talin, which then binds to actin filaments

A-actinin

Question 3

What is a focal adhesion

Answer 3

A focal adhesion is a discrete site on the cell that anchors it to the matrix.

Stress fibers attach to focal adhesions

Question 4

What is Leukocyte adhesion deficiency and what is its cause?

Answer 4

A deficiency in the ability of WBCs to adhere to the site of infection.

Caused by a defect in B2 subunit of integrins

Question 5

What is Glanzmann’s disease and its cause?

Answer 5

Platelets can’t bind to fibrinogen to initiate blood clotting, which leads to excessive bleeding.

Caused by missing or defecting B3 subunit

Question 6

What is the role of GP2B3A antagonists?

Answer 6

Used to prevent heart attacks and strokes by blocking platelet aggregation

Question 7

What are selectins and what is their function?

Answer 7

Cell-surface carbohydrate-binding proteins synthesized by endothelial cells (E), platelets (P), and WBCs (L).

They mediate initial weak adhesion between WBCs and endothelial cells

Question 8

What are ICAMS and what purpose do they serve?

Answer 8

Intracellular adhesion molecules that are expressed on endothelial cells.

Bind to integrins on WBCs and mediate a stronger interaction, trapping WBCs at inflammation sites.

Question 9

What are cadherins and what is their function?

Answer 9

Cadherins are Transmembrane glycoproteins that promote cell adhesion in tissues via homophilic binding

Question 10

What are the intermediate binding proteins for cadherins?

Answer 10

A-catenin
B-catenin

Bind cadherins to actin filaments

Question 11

What is the cause of Familial adenomatous polyposis?

Answer 11

Defect in the APC gene/protein

Prevents B-catenin from being degraded, upregulating gene expression

Question 12

What is the structure and function of adherens junctions?

Answer 12

Continuous belts around epithelial cells of cadherins and actin.

Connects cells to each other

Question 13

Describe the structure and function of desmosomes

Answer 13

Desmosomes connect cells via intermediate filaments

Cadherin-like proteins bind to intracellular proteins that bind to IFs

Question 14

What is Pemphigus and what is its cause?

Answer 14

Autoimmune disease that prevents the desmosomes from forming correctly

Affects skin and mucus membranes

Can affect desmosomes in the heart, causing it to come apart as it beats

Question 15

What is the structure and function of a hemidesmosome?

Answer 15

Connect cells to the ECM via intermediate filaments.

Use integrins as the linking protein

Intermediate proteins are Plectin and BP230.

Question 16

What three integral membrane proteins make up tight junctions?

Answer 16

Occludins
Claudins
JAMs

Question 17

What is the structure and function of gap junctions?

Answer 17

Structure - hexamers of connexins form connexons, connexons of neighboring cells link to form a gap junction.

Function - allow electrical and metabolic coupling of cytoplasm between neighboring cells. Permeability can be regulated.

Question 18

What is the presentation and cause of Charcot-Marie-Tooth disease?

Answer 18

Progressive degeneration of peripheral nerves, leading to loss of muscle control and muscle degeneration.

Mutation in connexin 32 gene in Schwann cells