This is neuroscience! Activation of photopigments ultimately causes: The activat

Question

This is neuroscience!

Activation of photopigments ultimately causes:

The activation of K+ channels causing efflux of potassium

The breakdown of cGMP resulting in the closure of cGMP gated ion channels

An increase in cGMP causing cGMP gated ion channels to open

An increase in cGMP causing cGMP gated ion channels to close

The activation of K+ channels causing efflux of potassium

The breakdown of cGMP resulting in the closure of cGMP gated ion channels

An increase in cGMP causing cGMP gated ion channels to open

An increase in cGMP causing cGMP gated ion channels to close

Explanation / Answer

When the photoreceptor cells are activated by the light, the pigment rhodopsin changes its shape. Rhodopsin contains 11 cis retinal. When it is activated by the light, it is converted to all trans retinal. Then, the regulatory protein transducin activates the enzyme cGMP phosphodiesterase which cleaves cGMP to 5'GMP. Reduction in cGMP causes the ion channels to close. This prevents the inflow of positive ions leading to hyperpolarisation of the cell and neurotransmitter release is stopped. Therefore, activation of photopigments ultimately causes the breakdown of cGMP resulting in the closure of cGMP gated ion channels. (option b)

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