BCH 3120 Lecture Notes - Lecture 12: Chromophore, Signal Transduction, Retinal Pigment Epithelium
16 Apr 2016
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Document Summary
Photoreceptors: transduce energy from photons into changes in membrane potential. Photopigment (protein with chromophore) changes conformation when absorbs light. Activates signal transduction cascade leading to graded changes in membrane potential and nt release. Structures specialized for light detection, encode direction, intensity of light, and contrasts. Evolutionary significance of the visible spectrum of light. Photoreceptors respond to a small portion of electromagnetic spectrum (300-1000nm) Photoreceptors evolved in aquatic ancestors: light attenuates in water, only some wavelengths penetrate into water column. Apical surface contains photopigments in microvillar projections. Ciliary membrane often highly folded into lamellae or disks containing photopigments. Distinct signal transduction mechanisms: rods and cones. Outer segment connected to inner segment by cilium. Outer segment composed of a series of membranous discs filled with photopigments. Inner segment connects to synaptic terminals: synapse with other cells, rod and cones structural and functional differences, # of photopigments expressed, roles in dim vs bright light, position on the retina.
