Cell Junctions and Adhesions

Question 1

Where are the cell junctions of a cell typically located?

Answer 1

On the basolateral side of the cell

Question 2

What’s the function of a tight junction? What’s its second name?

Answer 2

1. Controls passing of material tot he adjacent cells. It also protects from extracellular content, content outside and within the body (think about the kidneys and the urine it filters). Wraps around top lateral sides of the cell.
2. Zonula Occludens

Question 3

What is the tight junction adhesion particle?

Answer 3

Uses Claudins (binds to occludins and claudins of neighboring cells) and occluding protein. Note that they both interact with actin cytoskeleton.

Question 4

Explain how claudins plays an effect on the kidney filtration system.

Answer 4

Claudins 16 and 19 allow for the reabsorption of Ca2+ and Mg2+ into the body through tight junctions in the ascending limb. Mutation of these adhesion molecules yields low Mg in serum, high Ca2+ in the kidneys/urine, and calcifies the kidneys.

Question 5

What is the function of Belt Desmosome? What is its second name?

Answer 5

1. Its anchoring is cell to cell. It allows the body to go through constriction while being bound to other cells. This is more relevant during development when Apical Constriction and Invagination mechs take place.
2. Zonula Adherens

Question 6

What is the Belt Desmosome adhesion of choice? How does the cytoplasmic component work?

Answer 6

1. Cadherins (Ca2+ dependent)

2. Cytoplasmic side of the Cadherins has gamma and Beta subunit. They bind to the alpha subunit found in actin.

Question 7

The entire alpha, beta, and gamma complex found in the cytoplasmic side of belt desmosome is called:

Answer 7

Catenin

Question 8

How do E-Cadherins affect the cell to cell interactions present?

Answer 8

E-Cadherin loss prevents tight junction formation and contributes to epithelial ti mesenchymal transition. Not that mesenchymal cells have zero polarity, and lack cell adhesion and the ability to migrate and invade.

Question 9

How do P-Cadherins affect the cell to cell interactions present?

Answer 9

Loss of P-Cadherin leads to hair loss and blindness.

Question 10

Describe the spot desmosome. What is its second name? It’s Third name? What could you associate with spot desmosomes?

Answer 10

1. It works to anchor down the rest of the cell membrane. It fosters a cell to cell interaction. It uses Cadherins (desmocollin, desmogleins) as its adhesion of choice. It has a dense middle line between the cells. Cytoplasmic dense plaques hold desmoPLAKIN, PLAKoglobin, and PLAKophilin, all of which connect to the INTERMEIATE FILAMENTs. It has a super strong bond and looks like a ladder
2. Macula Adherins
3. Desmosome
4. PLAQUE

Question 11

List the lateral adhesion types from top to bottom in both names.

Answer 11

1. Tight junction, belt desmosome, spot desmosome

2. Zonula occludens, zonula adherins, Desmosome/Macula Adherins

Question 12

What do hemidesmosomes do?

Answer 12

They anchor the cell to the basement membrane. It fosters a cell to matrix interaction.

Question 13

What is an integrin? What does the interellular part do?

Answer 13

1. It interacts extracellularly with ECM protein. Has an alpha and beta subunit running antiparallel. It interacts with RGD (single letters of AA). The intercellular part interacts with cytoplasmic molecules, which interact with actin in the cytoskeleton.

Question 14

What is the adhesion molecule for Hemidesmosomes?

Answer 14

Integrin alpha6beta4

Question 15

What is a focal adhesion?

Answer 15

It is a type of cell junction which binds the cell to the matrix (fosters cell to matrix interaction). It’s transmembrane proteins are integrins and it binds to actin in the cytoskeleton.

Question 16

What illness is associated with a defect in spot desmosomes?

Answer 16

Pemphigus. Creates blisters WITHIN the epidermal layer (formign above the epidermus)

Question 17

What illness is associated with a defect with the hemidesmosomes?

Answer 17

Pemphigoid. It is the SPLITTING between the epidermus and the connecting tissue underlying it.

Question 18

What are connecting junctions? What’s its second name?

Answer 18

1. It’s purpose is mainly for communication. It uses connexins as its transmembrane proteins and it makes zero interactions with the cytoskeleton.
2. Gap junction

Question 19

What is a connexin?

Answer 19

In groups of 6 (which makes 1 connexon), has hydrophobic core so that small molecules (Ca2+) can pass through from cell to cell. pH, voltage etc can effect flow between the cells.

Question 20

What happens if regulation of Ca2+ flow fails?

Answer 20

Too mach Ca2+ may flow through, triggering apoptosis.

Question 21

Why is connexin 26 important?

Answer 21

It’s located in cochlear hair cells. Mutations here = deaf.

Question 22

Why is connexin 32 important?

Answer 22

It is located in peripheral myelin. Mutations here lead to slower signal receptions.

Question 23

What is a selectin?

Answer 23

(Ca2+ dependent) it binds to oligosaccharides and is expressed in lymphocytes, endothelial cells and platelets.

Question 24

What is an Immunoglobulin Superfamily Cell Adhesion Molecule (IgCAM)?

Answer 24

It contains Ig, is Ca2+ independent, and acts as a transmembrane protein. Used in leukocyte extravasasion process.

Question 25

Describe the leukocyte extravasasion process.

Answer 25

To fight off bacteria in the cell, leukocytes roll along endothelium with the attacking invaders. Rolling through selectins slows it down.. Once slow enough, integrins on the leukocytes bind to intracellular cell adhesion molecules (ICAM) and vascular CAM. The integrins then pull leukocyte through wall of endothelial blood vessels.

Question 26

Are leukocytes able to freely enter the endothelium?

Answer 26

No. They must break through all 3 layers (the ones studied in this card packet). Note that the integrin phase is the one responsible for pulling the leukocyte into the cell.