Definition
A Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria that allows the plant to absorb light - a process vital for photosynthesis.
Basics
Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from the Greek: chloros = "green" and phyllon = "leaf". Chlorophyll absorbs light most strongly in the blue and red but poorly in the green portions of the electromagnetic spectrum, hence the green colour of chlorophyll-containing tissues such as plant leaves. Chlorophyll was first isolated by Joseph Bienaimé Caventou and Pierre Joseph Pelletier in 1817.
Chlorophyll is vital for photosynthesis, which allows plants to obtain energy from light.
Chlorophyll molecules are specifically arranged in and around pigment protein complexes called photosystems which are embedded in the thylakoid membranes of chloroplasts. In these complexes, chlorophyll serves two primary functions. The function of the vast majority of chlorophyll (up to several hundred molecules per photosystem) is to absorb light and transfer that light energy by resonance energy transfer to a specific chlorophyll pair in the reaction center of the photosystems. Because of chlorophyll’s selectivity regarding the wavelength of light it absorbs, areas of a leaf containing the molecule will appear green.
The two currently accepted photosystem units are Photosystem II and Photosystem I, which have their own distinct reaction center chlorophylls, named P680 and P700, respectively. These pigments are named after the wavelength (in nanometers) of their red-peak absorption maximum. The identity, function and spectral properties of the types of chlorophyll in each photosystem are distinct and determined by each other and the protein structure surrounding them. Once extracted from the protein into a solvent (such as acetone or methanol), these chlorophyll pigments can be separated in a simple paper chromatography experiment, and, based on the number of polar groups between chlorophyll a and chlorophyll b, will chemically separate out on the paper.
The function of the reaction center chlorophyll is to use the energy absorbed by and transferred to it from the other chlorophyll pigments in the photosystems to undergo a charge separation, a specific redox reaction in which the chlorophyll donates an electron into a series of molecular intermediates called an electron transport chain. The charged reaction center chlorophyll (P680+) is then reduced back to its ground state by accepting an electron. In Photosystem II, the electron which reduces P680+ ultimately comes from the oxidation of water into O2 and H+ through several intermediates. This reaction is how photosynthetic organisms like plants produce O2 gas, and is the source for practically all the O2 in Earth's atmosphere. Photosystem I typically works in series with Photosystem II, thus the P700+ of Photosystem I is usually reduced, via many intermediates in the thylakoid membrane, by electrons ultimately from Photosystem II. Electron transfer reactions in the thylakoid membranes are complex, however, and the source of electrons used to reduce P700+ can vary
The electron flow produced by the reaction center chlorophyll pigments is used to shuttle H+ ions across the thylakoid membrane, setting up a chemiosmotic potential mainly used to produce ATP chemical energy, and those electrons ultimately reduce NADP+ to NADPH a universal reductant used to reduce CO2 into sugars as well as for other biosynthetic reductions.
Reaction center chlorophyll-protein complexes are capable of directly absorbing light and performing charge separation events without other chlorophyll pigments, but the absorption cross section (the likelihood of absorbing a photon under a given light intensity) is small. Thus, the remaining chlorophylls in the photosystem and antenna pigment protein complexes associated with the photosystems all cooperatively absorb and funnel light energy to the reaction center. Besides chlorophyll a, there are other pigments, called accessory pigments, which occur in these pigment-protein antenna complexes.
Chlorophyll is a chlorin pigment, which is structurally similar to and produced through the same metabolic pathway as other porphyrin pigments such as heme. At the center of the chlorin ring is a magnesium ion. For the structures depicted in this article, some of the ligands attached to the Mg2+ center are omitted for clarity. The chlorin ring can have several different side chains, usually including a long phytol chain. There are a few different forms that occur naturally, but the most widely distributed form in terrestrial plants is chlorophyll a. The general structure of chlorophyll a was elucidated by Hans Fischer in 1940, and by 1960, when most of the stereochemistry of chlorophyll a was known, Robert Burns Woodward published a total synthesis of the molecule as then known. In 1967, the last remaining stereochemical elucidation was completed by Ian Fleming, and in 1990 Woodward and co-authors published an updated synthesis.
Protochlorophyllide, more accurate monovinyl protochlorophyllide, is an immediate precursor of chlorophyll a that lacks the phytol side chain of chlorophyll. Unlike chlorophyll, protochlorophyllide is highly fluorescent; mutants that accumulate it glow in red if irradiated by the blue light. In Angiosperms, the last step, conversion of protochlorophyllide to chlorophyll, is light - dependent and such plants are pale (etiolated) if grown in the darkness. Gymnosperms, algae, and photosynthetic bacteria additionally have another, light - independent enzyme and grow green in the darkness as well.
Chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green colour of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to manufacture carbohydrates through photosynthesis and may die unless the cause of its chlorophyll insufficiency is treated, although some chlorotic plants, such as the albino Arabidopsis thaliana mutant ppi2 are viable if supplied with exogenous sucrose.
Culinary use: Chefs use chlorophyll to colour a variety of foods and beverages green, such as pasta and absinthe. Chlorophyll is not soluble in water and is first mixed with a small quantity of oil to obtain the desired result. Extracted Liquid Chlorophyll was considered unstable and always denatured, until 1997 when Frank S. & Lisa Sagliano used freeze-drying of liquid chlorophyll at the University of Florida and stabilized it as a powder, preserving it for future use.
Topics of Interest
Bacteriochlorophylls are photosynthetic pigments that occur in various phototrophic bacteria. They are related to chlorophylls, which are the primary pigments in plants, algae, and cyanobacteria. Groups that contain bacteriochlorophyll conduct photosynthesis, but do not produce oxygen. They use wavelengths of light not absorbed by plants. Different groups contain different types of bacteriochlorophyll.
Chlorophyllin, a food additive and alternative medicine, is a water-soluble, semi-synthetic sodium/copper derivative of chlorophyll.
A deep chlorophyll maximum, or DCM, is a subsurface maximum in the concentration of chlorophyll in the ocean or in lakes. Throughout much of the tropical ocean, the DCM is a permanent feature. At higher latitudes, it occurs seasonally. The presence of a DCM may indicate a maximum in the abundance of phytoplankton, or it may result from the higher chlorophyll content of phytoplankton living in a darker environment.
A grow light is an electric lamp designed to promote plant growth by emitting an electromagnetic spectrum appropriate for photosynthesis. The emitted light spectrum is similar to that from the sun, allowing indoor growth with outdoor conditions. Natural daylight has a high color temperature (approx. 6000 K) and appears bluish. Through the use of the color rendering index, it is possible to compare how much the lamp matches the natural color of regular sunlight. Recent advancements in LEDs have allowed for the production of relatively cheap, bright, and long lasting grow lights that emit only the wavelengths of light corresponding to chlorophyll's absorption peaks.
Chlorophyll a is a form of chlorophyll. Chlorophyll a is mainly used in light reactions used in photosynthesis. It loses excited electrons allowing them to move to the electron acceptor (redox reaction) which in turn moves it through the electron transport chain. It absorbs energy from the violet-blue and orange-red wavelengths. It has relatively high Kreft's dichromaticity index.Chlorophyll 'a' contains alternating single and double bonds, a phytol tail, and a central magnesium atom.
Chlorophyll b is a form of chlorophyll. Chlorophyll b helps in photosynthesis by absorbing light energy and it is more soluble than chlorophyll a because of its carbonyl group.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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