Cell Junctions Flashcards
What are cell junctions ?
They link cells together
How many types of cell junctions are there and what are they ?
There are 3 types of cell junctions
1) impermeable junctions (tight junctions)
2) anchoring junctions
3) communicating junctions (gap junctions)
What are the 2 different types of electron microscopy ?
1) conventional transmission electron microscopy
2) freeze fracture microscopy
How does transmission electron microscopy work ?
- take a thin tissue sample
- embed onto a hard plastic
- cut a thin section of the plastic (50nm)
- mount it onto a copper grid
- place grid into microscope
How does freeze fracture electron microscopy work ?
- take a thin tissue sample
- freeze in liquid nitrogen (196°)
- place in the special equipment
- bash it to break the tissue sample
- put it under a gold filament
- run an electric current through it
- a layer of gold will build up on the replica
- dissolve the tissue
Why do we use freeze fracture electron microscopy ?
Because it allows us to look at membrane surfaces due to the replica
What are the functions of tight junction proteins ?
TJP stop leakage between cells and allow a one way flow of materials between membranes
They also allow membrane proteins to stay in the region of the plasma membrane where they are needed
Give some examples of places which contain tight junction proteins ?
The bladder contains many tight junction proteins whereas parts of the kidney contain few tight junction proteins
What is the function of anchoring junctions ?
They attach the cytoskeleton of one cell to the cytoskeleton of another cell
They attach the cytoskeleton of one cell to its surroundings
What are the 2 types of anchoring junctions ?
1) adherens junctions - connect actin
2) desmosomes - connect intermediate filaments
What is pemphigus and how does it happen ?
It is an autoimmune disease where the skin cells separate because the body raises antibodies to the desmosomes which keep the cell membranes connected. It will look like huge blisters on the skin.
How were communicating junctions discovered ?
They were discovered by electrophysiologists
What is the role of a connexon ?
They line up and create aqueous channels between the cytosol of each cell
Give some examples of gap junctions in use
- coordination of the heartbeat
- coordination of smooth muscle contraction
- coordination of cilia in the respiratory system
