Retina, retinal rods

Answer Some individuals with Oguchi s disease have a defective rhodopsin kinase that slows the recycling of rhodopsin after its conversion to the all-trans form on illumination. This defect leaves retinal rod and cone cells insensitive for some time after a bright flash. Other individuals have genetic defects in arrestin that prevent it from interacting with phosphorylated rhodopsin to trigger the process that leads to replacement of all-brms-retinal with 11-c/s-retina.l. 

Keywords Amacrine cell Bipolar cell Cone Fovea Horizontal cell Muller cells Photoreceptor Retina Retinal ganglion cell Rod... 

In the eye, specialized photoreceptor cells of the retina, called rod cells are primarily responsible for low-light vision, with relatively little color detection. Rod cell outer segments contain lamellar protein disks rich in the protein opsin (Figure 19.26). Oxidation and isomerization of all-im/75 -retinol yields an intermediate, W-cis retinal, which is important in photoreception. The chemistry of photoreception is shown in Figure 19.27 and summarized as follows. 

A classic application of linear dichroism to study molecular orientations and motions in a complex biological system was R. Cone s study of induced dichroism in retinal rod outer segements [14]. Rhodopsin, the light-sensitive pigment-protein complex of the retina, contains 11-cw-retinal attached covalently to a protin (opsin) by a Schiff base linkage (Fig. 4.13A, B). Its transition dipole is oriented... 

The distribution of rods and cones is shown in Figure 3b centered about the fovea, the area of the retina that has the highest concentration of cones with essentially no rods and also has the best resolving capabiUty, with a resolution about one minute of arc. The fovea is nominally taken as a 5° zone, with its central 1° zone designated the foveola. There are about 40 R and 20 G cones for each B cone in the eye as a whole, whereas in the fovea there are almost no B cones. A result of this is that color perception depends on the angle of the cone of light received by the eye. The extremely complex chemistry involved in the stimulation of opsin molecules, such as the rhodopsin of the rods, and the neural connections in the retinal pathway are well covered in Reference 21. 

The retinol that is delivered to the retinas of the eyes in this manner is accumulated by rod and cone cells. In the rods (which are the better characterized of the two cell types), retinol is oxidized by a specific retinol dehydrogenase to become 2iW-trans retinal and then converted to 11-eis retinal by reti-... 

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