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Rhodopsin signal cascade diagram
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Rhodopsin-initiated Signal Transduction

Figure Legend, Left: In darkness, cGMP-gated ion channels in the photoreceptor’s outer segment are constantly open, allowing Na+ and Ca++ to depolarize the cell. This constant influx of positive charge creates a steady-state depolarization that stimulates continuous glutamate release from the photoreceptor’s synaptic terminal.
Right: When a photon of light hits rhodopsin, it changes the shape of retinal from its bent (cis) isoform to its straight (trans) isoform. The retinal isomerization affects the conformation of the entire rhodopsin protein. This activates the heterotrimeric G protein transducin (T). Transducin removes the inhibitor from cGMP phosphodiesterase (cGMP PDE). cGMP PDE catalyzes the hydrolysis of cGMP to GMP. This decreases the cGMP concentration, shutting off the cGMP-gated ion channels. The sudden stop in Na+ and Ca++ flow hyperpolarizes the cell, which attenuates glutamate release.

Purpose: Teach about the molecular pathway that turns light into meaningful changes in neurotransmitter volume. An iconic style was employed to increase clarity about the very complex process.

Target Audience: Advanced biology students

Medium: Adobe Illustrator