Light-harvesting complex
A light -harvesting complex ( engl. light harvesting complex, LHC) or antenna complex ( rarely also light collecting trap ) is a collection of membrane proteins in the photosynthetic membranes of organisms engaged in photosynthesis.
Function
Your task is to absorb light and to direct the energy to the reaction center, where the light reaction of photosynthesis takes place.
By the light absorption electrons are added in the pigment in an excited state. The absorbed energy is passed through a plurality of pigments, the so-called reaction centers. This energy transfer process is very fast ( picosecond range) and extremely efficient.
In the reaction center a charge separation will take place, which is the first step of the actual photosynthesis. It allows the conversion of ADP to ATP and NADP NADPH H , which ultimately, in the light- independent reaction of photosynthesis, results in the build-up of glucose molecules.
Structure of various light -harvesting complexes
The light -harvesting complexes of higher plants and algae are located in the inner membrane of chloroplasts ( thylakoid membrane ). Plants have a number of different light -harvesting complexes, which are all transmembrane proteins. They are assigned to various plant photosystems. That's the name of the main complex (major complex), which is associated with the photosystem 1, LHC1 complex (light harvesting complex 1 ), which associated with photosystem 2 complex LHC2. The latter represents the in terms of the number of common light-harvesting complex in the world and is among the most common protein resulting from the distribution of plants and algae at all. In addition to the main complexes, there are various other light-harvesting complex (minor complexes ), which are also arranged around the photosystems. These are usually given with CP and their weight in kilodaltons, eg CP29. The figure shows the structure of the LHC2 complex when you look on the thylakoid membrane. The pigments chlorophyll a (green), chlorophyll b ( cyan) and various carotenoids (yellow) are non-covalently by a protein scaffold ( transparent gray ) bound. The LHC2 complex is in this view a diameter of 7.3 nm It consists of three identical monomers of size 3.0 nm x 5.0 nm, with 8 chlorophyll a, chlorophyll b 6, 2 lutein, neoxanthin 1, 1 Xanthophyllzykluspigment ( violaxanthin, antheraxanthin or zeaxanthin ) and about 232 amino acids.
Purple bacteria in the light harvesting complexes are incorporated in the plasma membrane. It is like the case of plant light -harvesting complexes to transmembrane proteins. Most species have two types of light harvesting complexes, called LH1 and LH2. Some species also have a LH3, others exclusively LH1. All of the complexes have a ring-shaped structure consisting of identical subunits. The illustration shows for example, the complex of LH2 " Rhodopseudomonas acidophila ," which is composed of nine subunits. Each subunit consists of two closely spaced Bakteriochlorophyllen (red) and one to 90 ° tilted wide bacteriochlorophyll (orange, not in LH1 ) and a carotenoid ( yellow). The pigments are non-covalently by two short proteins ( transparent gray ) bound. LH1 is very similar in structure, but consists of more units, eg 16 As a result, a larger ring in the center of which gives rise to the reaction center is located.
Quantum physical phenomena
By femtosecond spectroscopy could be demonstrated that a reaching over the entire complex stable quantum entanglement of photons takes place, which makes it all possible efficient use of light energy without heat loss. Remarkable thing is, inter alia, the temperature stability of the phenomenon.