Chlorophyll 6985 224548828 2008-07-09T10:35:15Z 124.217.51.189 /* Chlorophyll and photosynthesis */ {{fixHTML|beg}} [[Image:Leavessnipedale.jpg|thumb|Chlorophyll gives leaves their green color]] {{fixHTML|mid}} [[Image:Chloroplasten.jpg|thumb|Chlorophyll is found in high concentrations in [[chloroplast]]s of plant cells.]] {{fixHTML|mid}} [[Image:AYool_SEAWIFS_annual.png|thumb|SeaWIFS-derived average sea surface [[chlorophyll]] for the period 1998 to 2006.]] {{fixHTML|end}} '''Chlorophyll''' is a green [[pigment]] found in most [[plant]]s, [[alga]]e, and [[cyanobacteria]]. Its name is derived from [[Greek language|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 color of chlorophyll-containing tissues like plant leaves.<ref>Speer, Brian R. (1997). [http://www.ucmp.berkeley.edu/glossary/gloss3/pigments.html "Photosynthetic Pigments"] in ''[http://www.ucmp.berkeley.edu/glossary/ UCMP Glossary (online)]''. University of California, Berkeley Museum of Paleontology. Verified availability [[March 12]], [[2007]].</ref> ==Chlorophyll and photosynthesis== 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 [[photosystem]]s which are embedded in the [[thylakoid]] membranes of [[chloroplast]]s. In these complexes, chlorophyll serves two primary functions. The function of the vast majority of chlorophyll (up to several hundred 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. There are currently two accepted photosystem units, Photosystem II and Photosystem I, which have their own distinct reaction center chlorophylls, named P680 and P700, respectively.<ref>Green, 1984</ref> These pigments are named after the wavelength (in [[nanometer]]s) 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<sup>+</sup>) is then reduced back to its ground state by accepting an electron. In Photosystem II, the electron which reduces P680<sup>+</sup> ultimately comes from the oxidation of water into O<sub>2</sub> and H<sup>+</sup> through several intermediates. This reaction is how photosynthetic organisms like plants produce O<sub>2</sub> gas, and is the source for practically all the O<sub>2</sub> in Earth's atmosphere. Photosystem I typically works in series with Photosystem II, thus the P700<sup>+</sup> 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<sup>+</sup> can vary. The electron flow produced by the reaction center chlorophyll pigments is used to shuttle H<sup>+</sup> ions across the thylakoid membrane, setting up a [[chemiosmosis|chemiosmotic]] potential mainly used to produce [[Adenosine triphosphate|ATP]] chemical energy, and those electrons ultimately reduce NADP<sup>+</sup> to [[NADPH]] a universal [[redox|reductant]] used to reduce CO<sub>2</sub> 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 pigment]]s, which occur in these pigment-protein antenna complexes. <div style="clear:both;"></div> ==Chemical structure== [[Image:Chlorophyll-a-3D-vdW.png|thumb|Space-filling model of the chlorophyll a molecule]] 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. 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.<ref>{{cite journal | author =R. B. Woodward, W. A. Ayer, J. M. Beaton, F. Bickelhaupt, R. Bonnett, P. Buchschacher, G. L. Closs, H. Dutler, J. Hannah, F. P. Hauck, S. Itô, A. Langemann, E. Le Goff, W. Leimgruber, W. Lwowski, J. Sauer, Z. Valenta, and H. Volz | title =The total synthesis of chlorophyll | journal =Journal of the American Chemical Society | volume =82 | pages =3800-3802 | date =1960 | url =http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/1960/82/i14/f-pdf/f_ja01499a093.pdf | doi = 10.1021/ja01499a093 }}</ref> In 1967, the last remaining stereochemical elucidation was completed by [[Ian Fleming (chemist)|Ian Fleming]],<ref>{{cite journal | author = Ian Fleming | title =Absolute Configuration and the Structure of Chlorophyll | journal =Nature | volume =216 | pages =151–152 | date =October 1967 | url =http://www.nature.com/nature/journal/v216/n5111/abs/216151a0.html | doi =10.1038/216151a0}}</ref> and in 1990 Woodward and co-authors published an updated synthesis.<ref>{{cite journal | author = Robert Burns Woodward, William A. Ayer, John M. Beaton, Friedrich Bickelhaupt, Raymond Bonnett, Paul Buchschacher, Gerhard L. Closs, Hans Dutler, John Hannah, Fred P. Hauck, ''et al.'' | title =The total synthesis of chlorophyll a | journal =Tetrahedron | volume =46 | issue = 22 | pages =7599-7659 | date =1990 | doi = 10.1016/0040-4020(90)80003-Z }}</ref> The different structures of chlorophyll are summarized below: {| class="wikitable" | ! Chlorophyll ''a'' ! Chlorophyll ''b'' ! Chlorophyll ''c1'' ! Chlorophyll ''c2'' ! Chlorophyll ''d'' |- | Molecular formula | C<sub>55</sub>H<sub>72</sub>O<sub>5</sub>N<sub>4</sub>Mg | C<sub>55</sub>H<sub>70</sub>O<sub>6</sub>N<sub>4</sub>Mg | C<sub>35</sub>H<sub>30</sub>O<sub>5</sub>N<sub>4</sub>Mg | C<sub>35</sub>H<sub>28</sub>O<sub>5</sub>N<sub>4</sub>Mg | C<sub>54</sub>H<sub>70</sub>O<sub>6</sub>N<sub>4</sub>Mg |- | C3 group | -CH=CH<sub>2</sub> | -CH=CH<sub>2</sub> | -CH=CH<sub>2</sub> | -CH=CH<sub>2</sub> | -CHO |- | C7 group | -CH<sub>3</sub> | -CHO | -CH<sub>3</sub> | -CH<sub>3</sub> | -CH<sub>3</sub> |- | C8 group | -CH<sub>2</sub>CH<sub>3</sub> | -CH<sub>2</sub>CH<sub>3</sub> | -CH<sub>2</sub>CH<sub>3</sub> | -CH=CH<sub>2</sub> | -CH<sub>2</sub>CH<sub>3</sub> |- | C17 group | -CH<sub>2</sub>CH<sub>2</sub>COO-Phytyl | -CH<sub>2</sub>CH<sub>2</sub>COO-Phytyl | -CH=CHCOOH | -CH=CHCOOH | -CH<sub>2</sub>CH<sub>2</sub>COO-Phytyl |- | C17-C18 bond | Single | Single | Double | Double | Single |- | Occurrence | Universal | Mostly plants | Various algae | Various algae | cyanobacteria |} {| | [[Image:chlorophyll_a.svg|thumb|Structure of chlorophyll ''a'']] | [[Image:chlorophyll_b.svg|thumb|Structure of chlorophyll ''b'']] | [[Image:chlorophyll_d.svg|thumb|Structure of chlorophyll ''d'']] |- | [[Image:chlorophyll_c1.svg|thumb|Structure of chlorophyll ''c1'']] | [[Image:chlorophyll_c2.svg|thumb|Structure of chlorophyll ''c2'']] |} When leaves degreen in the process of [[plant senescence]] chlorophyll is converted to a group of colorless [[tetrapyrrole]]s known as '''nonfluorescent chlorophyll catabolites''' (NCC's) with the general structure: :[[Image:Nonfluorescentchlorophilcatabolites.svg|Nonfluorescent chlorophyll catabolites]] These compounds have also been identified in several ripening fruits.<ref>''Colorless Tetrapyrrolic Chlorophyll Catabolites Found in Ripening Fruit Are Effective Antioxidants'' Thomas Muller, Markus Ulrich, Karl-Hans Ongania, and Bernhard Krautler [[Angew. Chem. Int. Ed.]] '''2007''', 46, 8699 –8702 {{DOI|10.1002/anie.200703587}}</ref> ==Spectrophotometry== [[Image:chlorophyll_ab_spectra.png|thumb|[[Absorbance]] spectra of free chlorophyll ''a'' (<font color=green>green</font>) and ''b'' (<font color=red>red</font>) in a solvent. The spectra of chlorophyll molecules are slightly modified ''in vivo'' depending on specific pigment-protein interactions.]] Measurement of the absorption of light is complicated by the solvent used to extract it from plant material, which affects the values obtained, *In diethyl ether, chlorophyll a has approximate absorbance maxima of 430 nm and 662 nm, while chlorophyll b has approximate maxima of 453 nm and 642 nm.<ref>Gross, 1991</ref> *The absorption peaks of Chlorophyll a are at 665 nm and 465 nm. Chlorophyll a fluoresces at 673 nm. The peak [[Molar absorptivity|molar absorption coefficient]] of chlorophyll a exceeds 10<sup>5</sup> M<sup>−1</sup> cm<sup>−1</sup>, which is among the highest for organic compounds. ==Biosynthesis== {{see|Chlorosis}} In [[plant]]s, chlorophyll may be synthesized from [[succinyl-CoA]] and [[glycine]], although the immediate precursor to chlorophyll ''a'' and ''b'' is [[protochlorophyll]]. Chlorosis is a condition in which [[leaf|leaves]] produce insufficient chlorophyll, turning them yellow. Chlorosis can be caused by a nutrient deficiency including [[Iron deficiency (plant disorder)|iron]] - called iron chlorosis, or in a shortage of [[Magnesium deficiency|magnesium]] or [[Nitrogen deficiency|nitrogen]]. Soil pH sometimes play a role in nutrient-caused chlorosis, many plants are adapted to grow in soils with specific pHs and their ability to absorb nutrients from the soil can be dependent on the soil pH.<ref>[http://plantanswers.tamu.edu/turf/iron.html Iron Chlorosis in Turfgrass<!-- Bot generated title -->]</ref> Chlorosis can also be caused by pathogens including viruses, bacteria and fungal infections or sap sucking insects. ==Culinary Use== Chefs use chlorophyll to color in green various dishes, such as pasta. Chlorophyll is not soluble in water and is first mixed with a small quantity of oil to obtain the desired result. ==See also== *[[Bacteriochlorophyll]], related compounds in phototrophic bacteria *[[Chlorophyllin]], a semi-synthetic derivative of chlorophyll *[[Grow light]], a lamp that promotes photosynthesis == References == {{Reflist}} ==External links== *[http://omlc.ogi.edu/spectra/PhotochemCAD/html/alpha.html Oregon University of Health & Sciences] * [http://www.mbl.ku.dk/mkuhl/pages/PDF/Larkum&Kuhl_2005.pdf PDF review-Chlorophyll d: the puzzle resolved] * [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=stryer.section.2670 Light Absorption by Chlorophyll] – NIH books {{-}} {{Botany}} {{Plant Pigments}} [[Category:Tetrapyrroles]] [[Category:Photosynthetic pigments]] [[ar:كلوروفيل]] [[bs:Hlorofil]] [[bg:Хлорофил]] [[ca:Clorofil·la]] [[cs:Chlorofyl]] [[cy:Cloroffyl]] [[da:Klorofyl]] [[de:Chlorophyll]] [[et:Klorofüll]] [[el:Χλωροφύλλη]] [[es:Clorofila]] [[eo:Klorofilo]] [[fa:سبزینه]] [[fr:Chlorophylle]] [[gl:Clorofila]] [[ko:엽록소]] [[hr:Klorofil]] [[id:Klorofil]] [[it:Clorofilla]] [[he:כלורופיל]] [[ka:ქლოროფილი]] [[lt:Chlorofilas]] [[hu:Klorofill]] [[mk:Хлорофил]] [[ms:Klorofil]] [[nl:Bladgroen]] [[ja:クロロフィル]] [[no:Klorofyll]] [[oc:Clorofilla]] [[pl:Chlorofil]] [[pt:Clorofila]] [[ro:Clorofilă]] [[qu:Raphi q'umir]] [[ru:Хлорофилл]] [[simple:Chlorophyll]] [[sk:Chlorofyl]] [[sl:Klorofil]] [[sr:Хлорофил]] [[su:Kloropil]] [[fi:Lehtivihreä]] [[sv:Klorofyll]] [[ta:பச்சையம்]] [[th:คลอโรฟิลล์]] [[vi:Diệp lục]] [[tr:Klorofil]] [[uk:Хлорофіл]] [[wa:Clorofile]] [[zh:叶绿素]]