706_S2006_PS2key - 7.06 Problem Set Two, 2006 1. You are...

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1 7.06 Problem Set Two, 2006 1. You are interested in studying epithelial polarity and how epithelial cell layers function to compartmentalize different extracellular spaces. Specifically, you would like to understand how the epithelium of the small intestine separates the lumen of the intestine on the apical surface from the blood on the basolateral surface, and how molecules such as glucose and amino acids are transported across this barrier. a) Draw a simple diagram of the intestinal epithelial cells. Include the microvilli (fingerlike projections that increase cell surface area and absorptive capacity) and the basal lamina. Label the apical surface and basolateral surface. (INSIDE OF INTESTINE) (BLOOD) There are more sophisticated figures in the text showing an epithelial layer if you wish to view them. b) Explain how a monolayer of cells (rather than a stratified multilayer of cells) can be sufficient to create an effective barrier that prevents the diffusion of macromolecules through the extracellular space between cells. A monolayer of cells is sufficient to create a barrier that seals the intestinal lumen from the blood because of tight junctions, which are rows of integral membrane proteins that completely surround the cell and interact with other tight junction integral membrane proteins on adjacent cells. Adjacent cells are in close contact where these rows of proteins interact, thus preventing the passage of macromolecules through the extracellular spaces between cells in a monolayer. c) You are aware of the body of scientific work using MDCK cells (Madin-Darby canine kidney cells) to study epithelial monolayers in culture. You are concerned that studying kidney cells may not allow you to answer the specific questions you have concerning transport of macromolecules in the intestine. After testing many cell lines and culture conditions, you Microvilli Basal lamina Apical surface Basolateral surface
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2 determine the appropriate conditions (which includes calcium in the media) that allow an intestinal cell line to differentiate into what appears to be mature absorptive enterocytes (intestinal absorptive cells) that display well-developed microvilli. In your experimental setup shown below, a confluent monolayer of intestinal epithelial cells grows on a filter. Your system allows you to add different media to the apical and basal compartments as well as to isolate the media from these two compartments. How would you determine whether these cultured cells can prevent the diffusion of the amino acid alanine across the cell monolayer? You would add your radiolabeled alanine to the appropriate growth media at physiological conditions (i.e. 37°C) to the apical compartment. After a period of incubation, you would assay for radioactivity in the basal compartment using, for example, a liquid scintillation counter. If there was no radioactivity, you would conclude that the epithelial cells formed cell-cell junctions that prevented the passage of radiolabeled alanine across the
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This note was uploaded on 01/23/2012 for the course BIOLOGY lsm1301 taught by Professor Seow during the Spring '11 term at National University of Singapore.

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706_S2006_PS2key - 7.06 Problem Set Two, 2006 1. You are...

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