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Facilitator QuestionsQ: Each mammalian rod outer segment has approximately 1,000 discs, each of which consists of a flattened lipid vesicle. What is the functional utility of this arrangement? Q: How does the focusing mechanism differ between a camera and the vertebrate eye? Q: Although not discussed in the lecture, it is interesting to note that photoreceptor outer segments are continuously synthesized throughout life, with about 10% of each rod outer segment assembled at its base and 10% discarded from its tip each day. Given that the discarded 10% of the outer segment is engulfed and digested by a specialized epithelial cell (which makes up a sheet of cells referred to as the retinal pigment epithelium, or RPE) and that each of these large epithelial cells performs this function for about 50 rods, how much biomass is an RPE cell digesting each day? Q: In complete darkness, mammalian rods occasionally exhibit changes in membrane current that are indistinguishable from single photon responses. These occur on average once per minute and each arises from the thermal isomerization of the 11–cis retinal chromophore within a single rhodopsin. Given that each mammalian rod has 40 million rhodopsins, calculate the average thermal stability of rhodopsin. Q: Consider the molecular mechanisms operating in different sensory systems, such as hearing, olfaction, vision, taste, and temperature sensation. Which ones use a cascade of enzyme reactions and which ones use a more direct response mechanism? |
