Sototransduction uses a signal transduction cascade similar to mechanisms stimul

Question

Sototransduction uses a signal transduction cascade similar to mechanisms stimulated by hormones and neurotransmitters. However, the visual sensory apparatus is stimulated by photons, and converts light energy into a nerve impulse. Determine whether each of the the following events increases phototransduction or does not increase phototransduction (either by not initiating a signal or by terminating the signal). The abbreviation cGMP is used for guanosine 3',5'-cyclic monophosphate (cyclic GMP), and PDE is used for phosphodiesterase.

Explanation / Answer

Due to Phototreansduction, following occurs-

1- When light energy is absorbed by rhodopsin, the rhodopsin begins to decompose; photoactivation of electrons in the retinal leads to instantaneous change of the 11-cis- retinal into all-trans-retinal.

2- Activated rhodopsin, activates a G protein called transducin- where Ta subunit dissociates, bound to a GTP.

3- Transducin activates phosphodiesterase, an enzyme that breaks down cGMP.

4- The drop in cGMP closes Na+ channels in the plasma membrane of the rod. As more sodium ions now leave the rod than leak back, their loss from inside the rod creates increased negativity inside the membrane, and greater the amount of light energy striking the rod, greater is the degree of hyperpolarization. (about -70 to -80 mV)

So, the grouping is done in a right way.

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