Cell junctions

Question 1

What are the different types of cell junctions?

Answer 1

-tight junction
-cell cell anchoring junctions
-channel forming junctions
-cell matrix anchoring junctions

Question 2

What are adherens junctions also known as and what are they made up of?

Answer 2

-AKA belt desmosomes
-made up of cadherins

Question 3

What is cadherin and what can it do?

Answer 3

-it’s a Ca2+ dependent adherin molecule
-makes homophilic interactions
-makes strong links between cells
-links to actin cytoskeleton

Question 4

What happens when the adhesion belt contracts?

Answer 4

-bottom of epithelial cells doesn’t, causing sheet of cells to bend
-tube pinches off - forms hollow, cylindrical tube

Question 5

What junctions link to the actin cytoskeleton?

Answer 5

-focal adhesions
-adherens junctions

Question 6

What are hemidesmosomes and what do they do?

Answer 6

-half a desmosome
-attach cells to basal lamina
-link integrin to intermediate filaments

Question 7

What do desmosomes do and where are they mainly found?

Answer 7

-form cell to cell junctions
-links cadherin to intermediate filaments
-found in heart muscle + epidermis

Question 8

What are the intermediate filaments in skin?

Answer 8

Keratin filaments

Question 9

What are desmosomes made up of?

Answer 9

-have adhesion points - strong connection points
-have cadherins as they’re cell-cell junctions
-filaments connect to cytoskeleton
-have a plaque of proteins that mediate the link

Question 10

What is Pemphigus?

Answer 10

-an autoimmune skin blistering disease
-attacks desmoglein - a cadherin that holds keratinocytes together in epidermis

Question 11

Where are tight junctions found?

Answer 11

In epithelia e.g gut

Question 12

What are the functions of tight junctions?

Answer 12

-prevent fluid, ion + membrane flow
-variable extent
-transcellular transport
-paracellular transport

Question 13

Describe the structure of tight junctions

Answer 13

-below plasma membrane + above microvilli
-not a single strip across cell - if there’s a puncture, the whole system would break down
-some appear as grooves + some as divots - depends on how membrane has been broken apart

Question 14

How can the membrane be split to make tight junctions appear differently?

Answer 14

-can split 2 separate bilayers
-can cleave middle of bilayer + peel single bilayer apart

Question 15

What is found in protein clusters in tight junctions and what is the most important?

Answer 15

-occludin + claudin
-occludin = most important

Question 16

Describe occludin and claudins

Answer 16

-occludin - highly conserved + found in all tight junctions
-claudins - assist occludin + around 20-25 types

Question 17

What do different claudins result in?

Answer 17

Different types of tight junction

Question 18

What other protein also associates with tight junctions?

Answer 18

-zonula occludens
-bind claudin, occludin + actin
-give structure rigor

Question 19

What do gap junctions do?

Answer 19

Allow regulated + directed cell-cell communication

Question 20

What is the structure of gap junctions?

Answer 20

-made of connexins
-connexins can be made up of 1 type of connexin (homomeric) or multiple (connexons)
-so can have many types of channel

Question 21

What are gap junctions regulated by?

Answer 21

-membrane potential, pH, Ca2+ and cell signals
-limit damage caused by Ca2+