Fototransdukció

Fototransdukció is the process by which living cells, primarily in the retina of the eye, convert light energy into electrical signals. This fundamental biological mechanism is crucial for vision in many organisms. In vertebrates, this process begins when photons of light strike photoreceptor cells, namely rods and cones. These cells contain specialized pigment molecules called photopigments, such as rhodopsin in rods and cone opsins in cones.

When light is absorbed by a photopigment, it causes a conformational change in the pigment molecule. This change triggers a cascade of biochemical reactions within the photoreceptor cell. Specifically, it leads to the activation of a G protein called transducin. Activated transducin then activates an enzyme called phosphodiesterase, which in turn hydrolyzes cyclic guanosine monophosphate (cGMP).

The reduction in cGMP levels causes ion channels in the cell membrane to close, leading to a hyperpolarization of the cell. This hyperpolarization is the electrical signal that is transmitted to other neurons in the retina, such as bipolar cells and ganglion cells. These signals are then processed and eventually sent to the brain via the optic nerve, where they are interpreted as visual images. Different types of cones, with varying opsins, are sensitive to different wavelengths of light, allowing for color vision. Rods are more sensitive to low light conditions and are responsible for black and white vision.