Chapter 4 Study Guide Flashcards
Know the functions of cell junctions:
mechanical anchorage and communication
Which junction is involved in communication rather than achorage?
The gap junction
Purpose of Tight Junctions:
Know that this is the junction most important if preventing passage of substance between cells. the places that these junctions are most imporatant are where you would not want leakage across an epithelial cell layer. For example: leakage of urine through the epithelium of the bladder, leakage of the acid contents of the stomach, leackage of unprocessed food through the gut.
Where would you most want a tight junction?
Places where you would not want leakage across an epithelial cell later, e.g. leakage of acid contents of the stomach
What is the main purpose of the tight junction?
most important in preventing passage of substance between cells.
Which junction is this: [PICTURE NEEDED]
Tight Junction
Purpose of Adherens Junctions:
Join cells together by transmembrane proteins called cadherins. Also attach the microfilaments of the cytoskeleton to the plasma membrane. This microfilament component forms a thick protein belt around the cell. Functionally important in resisting cell tearing during contractile activity e.g. in uterus or when food is moving through gut.
What are microfilaments made of?
Actin
Which junction is this: [PICTURE NEEDED]
Adherens Junctions
When do you most want an Adherens Junction?
Functionally important in resisting cell tearing during contractile activity, e.g. in uterus or when food is moving through gut.
Purpose of Desmosomes:
Also (like adherins junctions) join cells together by transmembrane proteins call cadherins. Attach to the cytoskeleton via intermediate filaments called keratins. Very common in the skin and in cardiac muscle cells.
Which junction is this: [PICTURE NEEDED]
Desmosomes
Purpose of Hemidesmosomes:
Similar to desmosomes but tey appear like half a desmosome since they occure when attaching a single cell to the basal lamina. The transmembrane proteins are called integrins.
Define term: cadherins
transmembrane proteins joining cells in the adherens junctions
Define term: microfilaments of the cytoskeleton
You will find microfilaments in most cells. They are the partner of microtubules. They are long, thin, and stringy proteins (mainly actin, but also myosin) compared to the rounder, tube-shaped microtubules. We’d like to say you can find them here or there, but they are everywhere in a cell. They work with microtubules to form the structure that allows a cell to hold its shape, move itself, and move its organelles.
Define term: Keratins
intermediate filaments that attach the desmosomes to the cytoskeleton
Define term: integrins
a family of trasmembrane proteins that function in cell adhesion; they are present in hemidesmosomes, whic anchor cells to a basement membrane, and they mediate adhesion of neutrophils to endothelial cells during emigration.
Purpose of Gap Junctions:
These are the junctions involved in cell/cell communication. Form structures called connexons. These are made up of proteins called connexins. They change conformation to open and close a central pore. Allow for transport of substances such as ions.
Define terms: connexons
Gap junctions form structures called connexons, which are made up of proteins called connexins
Define epithelial tissue:
A continuous sheet of cells with continuous borders that line a surface
Give examples of external locations for epithelial tissues
skin, cornea
Give examples of internal locations for epithelial tissues
digestive tract, peritoneal cavity, trachea, urinary system, hepatocytes (liver cels) and bile ducts, kidney duct cells
Where is the apical surface of the epithelial cell plasma membrane?
surface in contact with air of fluid (externally facing)
Where is the lateral surface of the epithelial cell plasma membrane?
surface in contact with adjacent epithelial cells