706_S2006_PS2 - 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. 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. 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 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? Apical Compartment Filter Basal Compartment Cell monolayer
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2 d) From the experiment you described above, you determine that there is some intercellular barrier that precludes the passage of macromolecules from the apical compartment to the basal compartment. Describe three ways by which you could determine whether the formation of tight junctions contributes to the existence of this barrier. e) You move on to studying the Na + /glucose symporter. Where is this protein located in intestinal cells? Where is the concentration of glucose higher, on the exoplasmic side or the cytosolic side of the membrane in which the Na + /glucose symporter is located? f)
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706_S2006_PS2 - 7.06 Problem Set Two 2006 1 You are...

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