Lecture 20 - Cells in their social context Flashcards
What is the requirement of cells working together as tissues?
Co-ordination of function within tissue requires cell-cell interaction and communication.
Protein sorting and membrane trafficking is essential for cells to function.
What causes cell polarity to exist?
Many cells generate and maintain an asymmetric distribution of cell surface components.
Why is it important to have cell polarity?
Cell-cell interactions
transport of solutes
cellular immunity
tissue development
What are epithelia and what is their function?
Epithelia are a monolayer of cells and form sheets. They form a barrier to water and solute movement and act to selectively allow molecules to enter.
What is the physiological function of epithelial tissue?
epithelia can transport ions and solutes between 2 compartments of the body. (like from gut to bloodstream)
What is the function of tight junctions found in epithelial tissue?
Tight junctions allow cells sheets to serve as barriers to solute diffusion.
What are the 2 domains of epithelial cells?
Apical plasma membrane
Basolateral plasma membrane
How are apical and basolateral regions separated in epithelial cells?
Apical and Basolateral plasma membranes are separated by a ring of tight junctions around the cell. These tight junctions prevent proteins and lipids of outer leaflet from diffusing between apical and basolateral regions.
What are the functions of the apical membrane?
Apical plasma membrane protects exposed surface from damage by outside environment.
Has organ specific functions (ion or nutrient uptake.)
Distinct protein composition
Distinct lipid composition (contains exclusively GPI anchors.)
Contains membrane transporters.
What are the fucntions of the basolateral domain?
Functions are different from the apical membrane and include forming an interface with body fluid.
The protein of basolateral membrane is distinct from the apical membrane.
Contains LDL receptors and growth factor receptors.
Contains Na+-K+-ATPase maintaining high potassium inside cells and high sodium outside cells.
How is glucose absorbed at the small intestine and moved to the bloodstream?
At apical surface: Active transport bring glucose into the cell at the apical surface.
At basolateral surface glucose carriers diffuse out of the cell via facilitated diffusion.
How do parietal cells create an acidic environment in the stomach?
Apical membrane contains a H+-K+ exchanger and a K+ channel. As a result potassium is pumped in in exchange with H+ and K+ diffuses back out via a K+ channel.
Basolateral membrane contains an Na+-K+-ATPase pump which pumps potassium into the cell in exchange for sodium.
Basolateral membrane also contains a Cl–HCO3 pump which removes HCO3 from the parietal cell and brings in chlorine to form HCL in the stomach. Apical membrane pumps this chlorine out into the stomach to forme the HCL.
How are polarized cells cultured?
1) Epithelial cell layer transfected with DNA encoding plasma membrane proteins.
2) Localize protein on surface of transfected cells by immunofluorescence.
3) Immunofluorescence can differentiate between apical and basolateral staining.
* in other words; stain, observe, and differentiate apical from basolateral.
What does a cultured polarized cell culture look like under the microscope?
When initially plated a subconfluent structure forms which has space between cells at this stage tight junctions have not been formed yet. Proteins just diffuse throughout the cell membrane. With time the cells create tight junctions and form a confluent tight monolayer.
How do membrane proteins reach the correct surface of polarized epithelial cells?
Direct pathway: Mostly done by kidneys. This is done by using separate vesicles for apical membrane proteins and basolateral membrane proteins. (kidney cells)
Indirect pathway: Initially vesicles transport both apical and basolateral proteins to the basolateral membrane. The apical proteins are then endocytosed and packaged into vesicles and transported to a basolateral early endosome and then to the apical membrane. (intestinal cells and hepatocytes)
