Which of the following events does NOT take place in rod cells upon light exposure_______________?
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Answer: D. Opening of Na+ channels
Explanation
Light exposure causes rhodopsin to activate transducin, which decreases intracellular cGMP and leads to sodium channel closure. In the dark, high cGMP levels keep sodium channels open, whereas light induces cGMP breakdown, causing channel closure. Therefore, the opening of sodium channels does not take place upon light exposure; instead, the channels actively close. Rod cells are specialized photoreceptor cells in the retina responsible for vision in low-light environment conditions. The process of visual phototransduction converts light photons into electrical neural signals sent to the brain. Closing sodium channels hyperpolarizes the photoreceptor cell membrane, reducing its release of neurotransmitters into synapses.
Structural changes in rhodopsin occur immediately when light photons strike the retinal chromophore inside the pigment. Activation of the G-protein transducin is a necessary subsequent step in the intracellular phototransduction cascade. Decreased intracellular cGMP concentration is the direct biochemical trigger responsible for closing the photoreceptor sodium channels.
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