True or false: Absorption of one photon is enough to activate rhodopsin?

True or false: Absorption of one photon is enough to activate rhodopsin?

• A. True
• B. False
• C. Depends on wavelength
• D. Only with multiple photons

Answer: (A)

Absorption of a single photon is enough to activate rhodopsin. When a photon is absorbed by the retinal chromophore (11-cis-retinal) in rhodopsin, it isomerizes to all-trans, converting rhodopsin into its active form, metarhodopsin II. This single activation then triggers a G-protein cascade via transducin, leading to a decrease in cGMP, closure of the cGMP-gated channels, and hyperpolarization of the rod cell. The phototransduction cascade amplifies this one-event trigger, so a single photon can produce a detectable signal. The other ideas aren’t correct because activation doesn’t require multiple photons, and the process occurs specifically when the photon energy matches rhodopsin’s absorption spectrum.

Absorption of a single photon is enough to activate rhodopsin. When a photon is absorbed by the retinal chromophore (11-cis-retinal) in rhodopsin, it isomerizes to all-trans, converting rhodopsin into its active form, metarhodopsin II. This single activation then triggers a G-protein cascade via transducin, leading to a decrease in cGMP, closure of the cGMP-gated channels, and hyperpolarization of the rod cell. The phototransduction cascade amplifies this one-event trigger, so a single photon can produce a detectable signal. The other ideas aren’t correct because activation doesn’t require multiple photons, and the process occurs specifically when the photon energy matches rhodopsin’s absorption spectrum.