1. Describe the appearance of a gap junction in TEM and in freeze fracture replicas. Describe how the observed structures are responsible for function.
2. Describe the general features of connexins.
3. Explain the relationship between connexins and connexons.
4. Describe an experiment that could be used to determine the size of molecules capable of passing through the gap junctions in an isolated sheet of epithelial tissue.
5. Briefly describe the role of tight junctions in the demarcation of different membrane domains (apical versus basolateral).
6. Describe the appearance of a tight junction in freeze fracture.
1. Indicate how the observed structures are responsible for function.
2. Indicate the major proteins responsible for the prominent features seen in freeze fracture replicas of tight junctions.
7. Describe an experiment using electron dense tracer materials and transmission electron microscopy that would demonstrate the occluding nature of tight junctions. Indicate how you would interpret the experimental results. What results would one see if the junction in question were a gap junction rather than a tight junction?
8. Distinguish between plakoglobin and desmoplakin in terms of their roles in a desmosome.
9. Is plakoglobin limited to desmosomes, or is it also present in other junctions? Explain.
10. What might one reasonably say about the "life style" of a sheet of epithelial cells in which one sees large numbers of desmosomes? Explain briefly.
11. Distinguish between integrins and cadherins in terms of the types of anchoring junctions in which they occur. Explain briefly.
12. Distinguish between a desmosome and an adherens junction in terms of function and appearance in TEM.
13. Distinguish between a gap junction and a tight junction in terms of function and appearance in TEM.
14. Compare and contrast desmosomes and hemidesmosomes in terms of location, structure, composition, and function.
15. Compare and contrast adherens junctions (particularly adhesion belts) and focal adhesions (aka focal contacts in chapter 16!) in terms of location, structure, composition, and function.
16. One does not find hemidesmosomes and focal contacts on the same cell at the same time. Why?
17. Thought (speculation?) question:   Why do you think the adhesion belts are necessary for the formation of tight junctions?
18. Identify (This list is not exhaustive!)



adherens junction	desmoplakin	integrin
adhesion belt	desmoglein, desmocollin	keratin filament
"anchoring fibrils"	desmosome	occludin
cadherin	E-cadherin	plakoglobin
claudin	focal adhesion (= focal contact )	plasmadesma
connexon	function of intermediate filaments	plectin
connexin	gap junction	sealing strand
cytokeratin	"hard" keratin	tight junction
cytoplasmic plaque	hemidesmosome

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