Cell Junctions

Question 1

What are the 6 major cell junctions?

Answer 1

• Tight junctions (AKA occluding junctions)
• Gap junctions
• Desmosomes
• Adherins junctions
• Hemidesmosomes
• Focal adhesions

Question 2

What are the functions of tight junctions?

Answer 2

• Seals gap between epithelial cells to prevent passing of molecules between cells
• Induces variable permeability

Question 3

Where are tight junctions distributed?

Answer 3

Found in all epithelia tissue

Question 4

What is the major protein vital for formation of tight junctions?

Answer 4

Claudins

Question 5

What are 2 proteins, other than claudins, involved in tight junctions? What do they both do?

Answer 5

1. Occludin - limits junctional permeability

2. Tricellulin - seals cell membranes together

Question 6

Are gap junctions uniform in size?

Answer 6

No

Question 7

What do gap junctions allow?

Answer 7

Regulated, direct cell-cell communication

Question 8

What are gap junctions made up of?

Answer 8

Connexins and innexins

allows ions through but not protein, mRNA etc.

Question 9

What is the function of gap junctions?

Answer 9

Creates direct channels between adjacent cells to allow passage of small, water-soluble molecules from cell to cell

Question 10

What factors regulated gap junctions?

Answer 10

• pH
• Calcium ions
• Voltage difference between two cells

Question 11

Why do calcium ions potentially close gap junctions?

Answer 11

To limit damage caused from excess calcium ions

Question 12

What are adherins junctions made from?

Answer 12

E cadherin

Question 13

Adherins junctions are _____-dependent

Answer 13

Ca^2+

Question 14

What kind of interaction does E cadherin have?

Answer 14

Homophilic, E cadherin only binds to E cadherin

Question 15

How are cadherins associated with the cytoskeleton?

Answer 15

Cadherins are bound to catenins which are bound to actin filaments of the cytoskeleton

Question 16

What is the function of adherins junctions?

Answer 16

Connects actin filaments in one cell with that of another to join cytoskeletons of adjacent cells

Question 17

Where are adherins junctions distributed?

Answer 17

• Epithelial tissues

- Heart where they anchor actin bundles on the contractile apparatus and link contractile cells end-to-end

Question 18

What structure do asherins junctions produce in epithelial cells? What does this structure allow for?

Answer 18

Adhesion belts AKA belt desmosomes, a continuous connection of actin filaments beneath apical surface of epithelia
Co-ordinated contraction of this belt allows for processes such as invagination and formation of tubes in morphogenesis

Question 19

In simple terms what do adhesion belts allow the conversion of?

Answer 19

Conversion of sheet of cells into a tubule

Question 20

What is the function of desmosomes?

Answer 20

Connect intermediate filaments in one cell to those in the adjacent cell to provide mechanical strength

Question 21

Which proteins do desmosomes use?

Answer 21

Similar cadherins

Question 22

Which junction do desmosomes connect?

Answer 22

Cell-cell

Question 23

What is the function of hemidesmosomes?

Answer 23

Anchor intermediate filaments in a cell to the extracellular matrix

Question 24

Which junction do hemidesmosomes connect?

Answer 24

Junction between cell and basal lamina of ECM

Question 25

What is the function of focal adhesions?

Answer 25

Anchor actin filaments in a cell to the extracellular matrix

Question 26

What is the transmembrane adhesion protein in both hemisdesmosomes and focal adhesions?

Answer 26

Integrins

Question 27

What is a clinical condition caused by the dysfunction of desmosomes? How does it cause its symptoms?

Answer 27

Pemphigus

Produces antibodies against a desmosome cadherin called desmoglein, causes skin blistering