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Green sulfur bacteria are life forms that use sun light as a main food
source. They
harvest the light by absorbing the sun's photons with their chlorosome
system, an assembly of
thousands of chlorophyll molecules. Absorption produces electronic
excitation of the chlorophyll molecules, but the excitation is only
short-lived (lifetime of about 1 nanosecond) and needs to be turned
quickly enough into a
more stable form of energy. The latter is achieved in a protein complex
called the reaction center, but for this purpose the
electronic excitation needs to travel from the chlorosome to the
reaction
center through a protein complex called the Fenna-Matthews-Olson (FMO)
protein. FMO is a crucial bottleneck, acting as an
energy faucet, through which the short-lived excitations need to
flow in a fraction of a nanosecond. Electronic
excitations are quantum phenomena highly sensitive to thermal noise.
Biophysicists spend much effort
to measure thermal effects on FMO electronic excitation flow. Now
researchers have complemented measurements through calculations and
have shown why FMO function is actually robust against thermal noise.
Using a
combination of classical and quantum mechanical calculations they
quantified the thermal noise present in FMO (reported recently
here and
here), and
determined that thermal noise greatly reduces quantum
coherent excitation in the transport through FMO (reported
here), but that
does not seem to be detrimental to
excitation flow. More information can be found here.