Editing 20110105 Lecture 4 notes.txt
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**These are diff because they are bound to cis-retinal which is isomerized when it absorbs a photon. | **These are diff because they are bound to cis-retinal which is isomerized when it absorbs a photon. | ||
**Cis-retinal then changes isomers to rhodopsin and we call it meta-rhodopsin because it is "activated". | **Cis-retinal then changes isomers to rhodopsin and we call it meta-rhodopsin because it is "activated". | ||
- | |||
*Meta-rhodopsin activates transducin, the g-protein. | *Meta-rhodopsin activates transducin, the g-protein. | ||
*Tranducin turns on phosphodiesterase which cleaves cGMP to straight chain GMP. | *Tranducin turns on phosphodiesterase which cleaves cGMP to straight chain GMP. | ||
**This causes a closing of the cGMP-gated cation channels. | **This causes a closing of the cGMP-gated cation channels. | ||
*Guanyly-cycase is constitutively activated, so there is a constant source of cGMP, but when phosphodiesterase is activated, the levels decrease. | *Guanyly-cycase is constitutively activated, so there is a constant source of cGMP, but when phosphodiesterase is activated, the levels decrease. | ||
- | **The constitutive activation assures that the neurons will not become too desensitized (because there will always be basal levesl of Na and Ca influx | + | **The constitutive activation assures that the neurons will not become too desensitized (because there will always be basal levesl of Na and Ca influx. |
- | *K+ channels in the outer segment cause hyperpolarization of the neuron when they allow efflux of K+ from the | + | *K+ channels in the outer segment cause hyperpolarization of the neuron when they allow efflux of K+ from the neuron. |
*There are three types of opsins which allows us to detect three colors of light. | *There are three types of opsins which allows us to detect three colors of light. | ||
*Rods absorb 500nm light | *Rods absorb 500nm light | ||
*Cones express three other types of opsins that absorb: 419nm (blue), 533nm (green), 564nm (long, yellow / red). | *Cones express three other types of opsins that absorb: 419nm (blue), 533nm (green), 564nm (long, yellow / red). | ||
+ | *cis-retinal is inherently and tightly bound in the receptor (it doesn't leave to be converted back to cis from meta). | ||
===Gustation (the sensation of tasting)=== | ===Gustation (the sensation of tasting)=== |