Sort the following events into the order that they take place in phototransduction in response to a flash of light. Your answer would be a four-letter string composed of letters A to E, e.g. BCDEA.
(A) The cGMP level drops.
(B) The cGMP level rises.
(C) The Ca²? level drops.
(D) Retinal isomerizes to an all-trans configuration.
(E) Gt exchanges its bound nucleotide.

Question

Sort the following events into the order that they take place in phototransduction in response to a flash of light. Your answer would be a four-letter string composed of letters A to E, e.g. BCDEA.
(A)	The cGMP level drops.
(B)	The cGMP level rises.
(C)	The Ca²? level drops.
(D)	Retinal isomerizes to an all-trans configuration.
(E)	Gt exchanges its bound nucleotide.

Quizplus · Accepted Answer

Light stimulation of rod photoreceptors isomerizes 11-cis retinal in rhodopsin to an all-?trans state. This changes the conformation of opsin and activates transducin (Gt) by nucleotide exchange. Gt then activates cyclic GMP phosphodiesterase to lower cyclic GMP levels and hence close cyclic-GMP-sensitive cation channels. Through a negative feedback loop, the resulting decrease in intracellular Ca²? concentration stimulates rapid replenishment of cyclic GMP.

Sort the Following Events into the Order That They Take