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These pigments enter a high-energy state upon absorbing a photon which they can release in the form of chemical energy. This can occur via light-driven pumping of ions across a biological membrane (e.g. in the case of the proton pump bacteriorhodopsin) or via excitation and transfer of electrons released by photolysis (e.g. in the photosystems ...
Each pigment absorbs light more efficiently in a different part of the electromagnetic spectrum. Chlorophyll a absorbs well in the ranges of 400–450 nm and at 650–700 nm; chlorophyll b at 450–500 nm and at 600–650 nm. Xanthophyll absorbs well at 400–530 nm.
Photoreceptor proteins typically consist of a protein attached to a non-protein chromophore (sometimes referred as photopigment, even so photopigment may also refer to the photoreceptor as a whole). The chromophore reacts to light via photoisomerization or photoreduction , thus initiating a change of the receptor protein which triggers a signal ...
Two examples of carotenoids are lycopene and β-carotene. These molecules also absorb light most efficiently in the 400 – 500 nm range. Due to their absorption region, carotenoids appear red and yellow and provide most of the red and yellow colours present in fruits and flowers. The carotenoid molecules also serve a safeguarding function.
The process starts when light is absorbed by two BChl molecules that lie near the periplasmic side of the membrane. This pair of chlorophyll molecules, often called the "special pair", absorbs photons at 870 nm or 960 nm, depending on the species and, thus, is called P870 (for Rhodobacter sphaeroides ) or P960 (for Blastochloris viridis ), with ...
Each photoreceptor absorbs light according to its spectral sensitivity (absorptance), which is determined by the photoreceptor proteins expressed in that cell. Humans have three classes of cones (L, M, S) that each differ in spectral sensitivity and 'prefer' photons of different wavelengths (see graph). For example, the peak wavelength of the S ...
The various cone cells are maximally sensitive to either short wavelengths (blue light), medium wavelengths (green light), or long wavelengths (red light). Rod photoreceptors only contain one type of photopigment, rhodopsin, which has a peak sensitivity at a wavelength of approximately 500 nanometers which corresponds to blue-green light. [6]
Electrons within these molecules are promoted to a higher-energy state. This is one of two core processes in photosynthesis, and it occurs with astonishing efficiency (greater than 90%) because, in addition to direct excitation by light at 680 nm, the energy of light first harvested by antenna proteins at other wavelengths in the light ...