9.3 Cell Junctions Flashcards
Tight junctions
(occludens junctions) Found at the top of a polarized cell. They restrict the movement of extracellular fluid past the cell. They also restrict the movement of membrane components from one cell compartment to another.
Anchoring junctions
Physical structures that attach cells to each other or to their surroundings and the extracellular matrix.
There are 3 types:
- Adherence junctions
- Desmosome
- Hemidesmosome
Communication junctions
Allow movement of small ions and other signals between cells. Communication junctions are not physically strong and lack attachment to the cytoskeleton.
In invertebrates, the cell junction that would be similar to tight junctions in vertebrates is called _______ .
Septate junction.
What types of cell junctions do you find actin filaments associated with?
Adherence junctions (type of anchoring junction)
Tight junctions are formed by the transmembrane proteins _____ and _____.
Claudin and occludin
Occludin
(light green) Transmembrane protein that forms sealing strands in tight junctions
Claudin
(darker green) Transmembrane protein that forms sealing strands in tight junctions
The protein that forms septate junctions in invertebrates is called _________ .
Discs-large
Anchoring junctions have both ______ anchor proteins and _____ adhesion proteins.
intracellular/transmembrane
What are the 2 classes of Anchoring Junctions?
- Cell-to-cell
2. Cell-matrix
Integrins
calcium-dependent cell-matrix adhesion molecules with cytoskeletal support. Integrins are heterodimers, with an alpha and beta subunit.
Desmosomes
Form strong connections between cells. Most common in mechanically stressed tissues.
Desmosomes and Hemidesmosomes are stronger than _______.
Actin supported junctions (adherens junctions)
Communication junctions
Lack supporting cytoskeletal elements and are thought of as a specialized transmembrane pore that is formed between 2 neighboring cells.
In animals, communication junctions are called _______.
Gap junctions
Connexon
A communication junction channel is formed by a hexagonal group of 6 proteins created by cells called connexons. 2 connexon channel structures form a communication channel.
Connexins
The proteins that make up connexons
What is the function of a communication junction?
Allows electrical signals and small but not large molecules to move between cells
What is the general structure of an Anchoring junction?
Every anchoring junction has intracellular anchor proteins and transmembrane adhesion proteins.
Focal adhesions are found at the ends of ____________ .
Actin filament bundles.
Focal Adhesion
Cell to matrix junctions and are supported by actin filaments. They have Integrin instead of Cadherin as their transmembrane protein and Vinculin, alpha actinin and filamin as intracellular coupling proteins.
Plasmodesmata
Channels of cytoplasm that join neighboring plant cells through small holes in the cell wall.
Desmotubules
ER derived membrane tubes found in the center of plasmodesmata.
