Define cell-cell junctions.
specialized connection between the plasma membranes of adjoining cells for the purpose of adhesion, sealing or communication
What are the two main kinds of adhesive junctions?
How do adhesive junctions join cells together?
adherens and desmosomes
anchor the cytoskeleton to the cell surface
How do adherens junctions work?
there are continuous zones of attachment
the protein called beta-catenin binds to the cytosolic tail of the cadherin
p120catenin binds to the cytoplasmic tail of caherins near the plasma membrane
How do desmosomes work?
button-like points of strong adhesion between adjacent cells in a tissue
abundant in the skin, heart muscle, and the neck of the uterus
desmosomes have fingerlike projections called tonofilaments
Define tight junction.
type of cell junction in which the adjacent plasma membranes of neighboring animal cells are tightly sealed, thereby preventing molecules from diffusing from one side of an epithelial cell layer to the other by passing through the spaces between adjoining cells
Do tight junctions span the entire membrane?
Tight junctions are connected along sharp defined ridges
As seen by freeze fracture microscopy
What is a tight junctions role in the membrane?
tight junctions act like "gates" preventing the movement of fluids, ions, and molecules between cells
Tight junctions also act like "fences", blocking the lateral movement of lipids and proteins within the membrane
What are the major transmembrane proteins of tight junctions?
occludin and junctional adhesion molecules (JAMs)
transmembrane protein that forms the main structural component of a tight junction
define paracellular transport.
a type of cellular transport in which ions move between, rather than through, cells
What does the claudin structure look like?
four membrane domains and extra and intracellular loops.
the largest extracellular loop contains charged amino acids that are though to interact with claudins on a neighboring cell to create a paracellular pore through which ions can pass
What is a gap junction?
a gap junction is a region where the plasma membranes of two cells are aligned and brought into intimate contact, with a gap of only 2-3 nm in between
What does the gap junction provide for the cell?
the gap junction provides a pont of cytoplasmic contact between two adjacent cells through which ions and small molecules can pass
What does a gap junction look like?/What does a gap junction consist of?
gap junctions are made of things called connexons (which is a cylindrical arrangement of connexins)
connexons form direct channels between cells allowing only specific sized things to pass through as the channel is only 3nm wide