Light-harvesting complex

85:, and the rate depends strongly on the distance between the energy donor and energy acceptor molecules. Before an excited molecule can transition back to its ground state, energy needs to be harvested. This excitation is transferred among chromophores where it is delivered to the reaction centre. Light-harvesting complexes have their pigments specifically positioned to optimize these rates. 214: 75:

Photosynthesis is a process where light is absorbed or harvested by pigment protein complexes which are able to turn sunlight into energy. Absorption of a photon by a molecule takes place when pigment protein complexes harvest sunlight leading to electronic excitation delivered to the reaction centre

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matches that of an electronic transition. The fate of such excitation can be a return to the ground state or another electronic state of the same molecule. When the excited molecule has a nearby neighbour molecule, the excitation energy may also be transferred, through electromagnetic interactions,

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is known as the phycobilisome which is composed of linear tetrapyrrole pigments. Pigment-protein complexes referred to as R-phycoerythrin are rod-like in shape and make up the rods and core of the phycobilisome. Little light reaches algae that reside at a depth of one meter or more in seawater, as

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Purple bacteria is a type of photosynthetic organism with a light harvesting complex consisting of two pigment protein complexes referred to as LH1 and LH2. Within the photosynthetic membrane, these two complexes differ in terms of their arrangement. The LH1 complexes surround the reaction centre,

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subunits that radiate out from this center like thin tubes. This increases the surface area of the absorbing section and helps focus and concentrate light energy down into the reaction center to form chlorophyll. The energy transfer from excited electrons absorbed by pigments in the

242:, are the chromophores that bind through a covalent thioether bond to their apoproteins at cystein residues. The apoprotein with its chromophore is called phycocyanin, phycoerythrin, and allophycocyanin, respectively. They often occur as hexamers of α and β subunits (α 122:

The main light harvesting complex in Green bacteria is known as the chlorosome. The chlorosome is equipped with rod-like BChl c aggregates with protein embedded lipids surrounding it. Chlorosomes are found outside of the membrane which covers the reaction centre.

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alone. The light which is captured by the chromophores is capable of exciting molecules from their ground state to a higher energy state, known as the excited state. This excited state does not last very long and is known to be short-lived.

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Lokstein (1994)The role of light-harvesting complex II energy dissipation: an in-vivo fluorescence in excess excitation study on the origin of high-energy quenching. Journal of Photochemistry and Photobiology 26:

184:. 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 824:"The primary structure of the antenna polypeptides of Ectothiorhodospira halochloris and Ectothiorhodospira halophila. Four core-type antenna polypeptides in E. halochloris and E. halophila" 51:

Light-harvesting complexes are found in a wide variety among the different photosynthetic species, with no homology among the major groups. The complexes consist of proteins and

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Brunisholz RA, Zuber H (1992). "Structure, function and organization of antenna polypeptides and antenna complexes from the three families of Rhodospirillaneae".

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The carotenoid molecules also serve a safeguarding function. Carotenoid molecules suppress damaging photochemical reactions, in particular those including

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The geometrical arrangement of a phycobilisome is very elegant and results in 95% efficiency of energy transfer. There is a central core of

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Light Harvesting by Phycobilisomes Annual Review of Biophysics and Biophysical Chemistry Vol. 14: 47-77 (Volume publication date June 1985)

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and carotenoids to gather light energy. These proteins are arranged in a ring-like fashion creating a cylinder that spans the membrane.

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are important in light-harvesting complexes present in plants. Chlorophyll b is almost identical to chlorophyll a, except it has a

293: 765:"The molecular mechanisms of light adaption in light-harvesting complexes of purple bacteria revealed by a multiscale modeling" 706:"The molecular mechanisms of light adaption in light-harvesting complexes of purple bacteria revealed by a multiscale modeling" 647:"The molecular mechanisms of light adaption in light-harvesting complexes of purple bacteria revealed by a multiscale modeling" 1338: 199:, which exposure to sunlight can cause. Plants that lack carotenoid molecules quickly die upon exposure to oxygen and light. 254:. They enhance the amount and spectral window of light absorption and fill the "green gap", which occurs in higher plants. 64: 1595: 1636: 1641: 1697: 1656: 131:

use ellipsoidal complexes known as the chlorosome to capture light. Their form of bacteriochlorophyll is green.

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while the LH2 complexes are arranged around the LH1 complexes and the reaction centre in a peripheral fashion.

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subunits at the periphery of these antennas appears at the reaction center in less than 100 ps.

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Liu et al. (2004) Crystal structure of spinach major light-harvesting complex at 2.72A° resolution.

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Ramos, Felipe Cardoso; Nottoli, Michele; Cupellini, Lorenzo; Mennucci, Benedetta (2019-10-30).

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Ramos, Felipe Cardoso; Nottoli, Michele; Cupellini, Lorenzo; Mennucci, Benedetta (2019-10-30).

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Ramos, Felipe Cardoso; Nottoli, Michele; Cupellini, Lorenzo; Mennucci, Benedetta (2019-10-30).

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MacColl (1998) Cyanobacterial Phycobilisomes. JOURNAL OF STRUCTURAL BIOLOGY 124(2-3): 311-34.

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that have alternating single and double bonds along their length. Such molecules are called

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