detection of visible light

Definition

Target type: biologicalprocess

The series of events in which a visible light stimulus is received by a cell and converted into a molecular signal. A visible light stimulus is electromagnetic radiation that can be perceived visually by an organism; for organisms lacking a visual system, this can be defined as light with a wavelength within the range 380 to 780 nm. [GOC:go_curators, ISBN:0198506732]

The detection of visible light, a crucial process for many organisms, begins with the absorption of photons by specialized light-sensitive cells called photoreceptor cells. These cells, located in the retina of the eye in animals, contain pigments that undergo a conformational change upon light absorption. In humans, the primary photoreceptor pigments are rhodopsin and photopsin. Rhodopsin, found in rod cells, is responsible for dim light vision and is highly sensitive to light. Photopsin, found in cone cells, is responsible for color vision and is less sensitive to light. When a photon of light strikes rhodopsin, it triggers a cascade of events that ultimately leads to a change in membrane potential, signaling the presence of light. This process begins with the absorption of a photon by retinal, a molecule bound to opsin, the protein component of rhodopsin. This absorption causes retinal to undergo a conformational change from its cis form to its trans form. This change activates opsin, which in turn activates a G protein called transducin. Activated transducin then activates phosphodiesterase, an enzyme that breaks down cyclic GMP (cGMP). cGMP is normally bound to sodium channels in the plasma membrane of photoreceptor cells, keeping them open. The breakdown of cGMP causes the sodium channels to close, reducing the influx of sodium ions and hyperpolarizing the cell. This hyperpolarization is the signal that is transmitted to the brain via the optic nerve, conveying information about the presence and intensity of light. The phototransduction cascade is incredibly sensitive, capable of detecting just a few photons of light. This sensitivity is achieved through several mechanisms, including amplification at each step of the cascade and the use of feedback mechanisms to fine-tune the response. The process also involves a rapid inactivation phase, allowing the photoreceptor cells to quickly recover and respond to subsequent light stimuli. This intricate process of light detection and signal transduction allows organisms to perceive their environment and navigate their surroundings. It is essential for a wide range of biological processes, including vision, circadian rhythm regulation, and plant growth.'
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Proteins (2)

Compounds (32)