Intracellular junctions - based on e and p notes

Question 1

Gap Junctions
. Outline structure

Answer 1

Structure = 2 connexons that form a channel, 1 in each cell membrane, each is made of 6 connexins
6 connexins = 1 connexon
2 connexon = 1 channel

Question 2

Purpose of Gap junctions & locations gap junction is found in

Answer 2

. Purpose = passage of small ions & molecules (2nd messengers) between adjacent cells
Location
epithelial cells, smooth muscle cells, cardiac cells - creates an ELECTRICAL SYNCYTIUM

Question 3

Fill in the blanks - GAP JUNCTIONS
Allow …. communication and passage of ……..Create a direct …… between 2 cells2 ….., 1 in each cell membrane, each one is made of …..Couples cells ….
The proteins are rapidly renewed- short half-life of a few hours for a connexinTheir permeability is highly regulated by calcium concentration and cellular pH (so mass cell death does not occur as high calcium -prolonged cytosolic calcium elevation is an apoptosis signal)

Answer 3

intracellular, ions and small molecules
channel
connexons 6 connexins
electrically and mechanically

Question 4

Tight junctions
Name and elaborate on the proteins found in tight junctions

Answer 4

Proteins = occludins, claudins, zona occludins and actin filaments
Zona occludins and actin filaments = cytosolic side
Occludins and claudins = between one tight junction and the next one

Question 5

What does the term trans-epithelial transport mean?

Answer 5

. Trans-epithelial transport - the selective movement of molecules & ions through diffusion, cotransport & active transport - often driven by the movement of sodium

Question 6

Compare the junctional complexes for transepithelial transport at leaky epithelia versus tight epithelia

Answer 6

Leaky epithelia = does not have tight junctions or has less complex tight junctions such as - e.g. kidney proximal tubule
Tight epithelia = has tight junctions that prevent most movement between cells

Question 7

Names of anchoring junctions

Answer 7

. Desmosomes & Hemidesmosomes
Adherens Junctions - Actin-linked cell-matrix adhesion/ focal adhesions

Question 8

Desmosomes - recall facts

Answer 8

Links intermediate filaments of adjacent cells together
Use anchor proteins to attach the intermediate filaments to the membrane and each other
Adhesion proteins (cadherins) then attach the junctions together
Provide mechanical strength- often found in epithelial tissue (mechanical stress)

Question 9

Hemidesomosomes - recall facts

Answer 9

Anchors intermediate filaments to the ECM

Question 10

Adherens junctions - recall facts

Answer 10

Connects actin bundles in adjacent cells

Resist extension and pulling forces exerted by adjacent cells

Question 11

Actin-linked cell-matrix adhesions/ focal adhesions:

Answer 11

Connects actin bundles in a cell to the ECM

Question 12

State the purpose of anchoring junctions

Answer 12

These junctions are used structurally to hold cells together (they ‘spot-weld’ cells), join cytoskeletal proteins together using cadherins- different types for different junctions/ intermediate filaments in desmosomesNormally symmetrical junctions because cadherins attach to the same type of cadherin

Question 13

Tight junctions - recall facts

Answer 13

Highly dynamic seal that constantly adjusts the paracellular permeability- can have no gaps between cells
A barrier to harmful substances but can allow the passage of nutrients and specially designed drugs
The permeability of these tight junctions can change between tissue types and the requirements of that tissueFound in epithelial tissues to create 2 distinct apical and basolateral domains (barrier)
Adhesion proteins connect the 2 plasma membranes (often claudins), homophilic and transmembrane
Occludins are used to limit junction permeability
Tricellulin is used to seal cells at a 3-cell junction
Extracellular domains adhere to make the junction impermeable
Scaffold proteins help form the junction and are part of the junctional complex to support it (e.g., zona occludens)