What occurs upon light stimulation in a vertebrate photoreceptor cell?

What occurs upon light stimulation in a vertebrate photoreceptor cell?

• A. cGMP levels increase due to conversion to GMP
• B. cGMP levels decrease due to conversion to GMP
• C. cGMP levels remain unchanged
• D. cGMP levels increase due to GTP conversion

Answer: (B)

In vertebrate photoreceptor cells, light stimulation leads to a significant biochemical response that affects the levels of cyclic guanosine monophosphate (cGMP). When these cells are exposed to light, a cascade of events is triggered that results in the activation of a phosphodiesterase enzyme. This enzyme catalyzes the breakdown of cGMP into GMP, causing a decrease in the levels of cGMP in the cell. The reduction in cGMP is crucial because cGMP is responsible for keeping certain ion channels open in the photoreceptor cell membrane, allowing sodium ions to flow in and maintain a depolarized state in darkness. With light exposure and the subsequent decrease in cGMP levels, these ion channels close, leading to hyperpolarization of the photoreceptor cell. This change in membrane potential is transformed into electrical signals that are then transmitted to the brain, allowing us to perceive light. Thus, the correct understanding here is that the phototransduction pathway initiated by light results in the conversion of cGMP to GMP, leading to a decrease in cGMP levels.

In vertebrate photoreceptor cells, light stimulation leads to a significant biochemical response that affects the levels of cyclic guanosine monophosphate (cGMP). When these cells are exposed to light, a cascade of events is triggered that results in the activation of a phosphodiesterase enzyme. This enzyme catalyzes the breakdown of cGMP into GMP, causing a decrease in the levels of cGMP in the cell.

The reduction in cGMP is crucial because cGMP is responsible for keeping certain ion channels open in the photoreceptor cell membrane, allowing sodium ions to flow in and maintain a depolarized state in darkness. With light exposure and the subsequent decrease in cGMP levels, these ion channels close, leading to hyperpolarization of the photoreceptor cell. This change in membrane potential is transformed into electrical signals that are then transmitted to the brain, allowing us to perceive light.

Thus, the correct understanding here is that the phototransduction pathway initiated by light results in the conversion of cGMP to GMP, leading to a decrease in cGMP levels.