Chlorophyll

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Chlorophyll (also chlorophyl) is any of several related green pigments found in the mesosomes of cyanobacteria and in the chloroplasts of algae and plants. Chlorophyll_sentence_0

Its name is derived from the Greek words χλωρός, khloros ("pale green") and φύλλον, phyllon ("leaf"). Chlorophyll_sentence_1

Chlorophyll is essential in photosynthesis, allowing plants to absorb energy from light. Chlorophyll_sentence_2

Chlorophylls absorb light most strongly in the blue portion of the electromagnetic spectrum as well as the red portion. Chlorophyll_sentence_3

Conversely, it is a poor absorber of green and near-green portions of the spectrum, which it reflects, producing the green color of chlorophyll-containing tissues. Chlorophyll_sentence_4

Two types of chlorophyll exist in the photosystems of green plants: chlorophyll a and b. Chlorophyll_sentence_5

History Chlorophyll_section_0

Chlorophyll was first isolated and named by Joseph Bienaimé Caventou and Pierre Joseph Pelletier in 1817. Chlorophyll_sentence_6

The presence of magnesium in chlorophyll was discovered in 1906, and was that element's first detection in living tissue. Chlorophyll_sentence_7

After initial work done by German chemist Richard Willstätter spanning from 1905 to 1915, the general structure of chlorophyll a was elucidated by Hans Fischer in 1940. Chlorophyll_sentence_8

By 1960, when most of the stereochemistry of chlorophyll a was known, Robert Burns Woodward published a total synthesis of the molecule. Chlorophyll_sentence_9

In 1967, the last remaining stereochemical elucidation was completed by Ian Fleming, and in 1990 Woodward and co-authors published an updated synthesis. Chlorophyll_sentence_10

Chlorophyll f was announced to be present in cyanobacteria and other oxygenic microorganisms that form stromatolites in 2010; a molecular formula of C55H70O6N4Mg and a structure of (2-formyl)-chlorophyll a were deduced based on NMR, optical and mass spectra. Chlorophyll_sentence_11

Photosynthesis Chlorophyll_section_1

Chlorophyll is vital for photosynthesis, which allows plants to absorb energy from light. Chlorophyll_sentence_12

Chlorophyll molecules are arranged in and around photosystems that are embedded in the thylakoid membranes of chloroplasts. Chlorophyll_sentence_13

In these complexes, chlorophyll serves three functions. Chlorophyll_sentence_14

The function of the vast majority of chlorophyll (up to several hundred molecules per photosystem) is to absorb light. Chlorophyll_sentence_15

Having done so, these same centers execute their second function: the transfer of that light energy by resonance energy transfer to a specific chlorophyll pair in the reaction center of the photosystems. Chlorophyll_sentence_16

This pair effects the final function of chlorophylls, charge separation, leading to biosynthesis. Chlorophyll_sentence_17

The two currently accepted photosystem units are photosystem II and photosystem I, which have their own distinct reaction centres, named P680 and P700, respectively. Chlorophyll_sentence_18

These centres are named after the wavelength (in nanometers) of their red-peak absorption maximum. Chlorophyll_sentence_19

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. Chlorophyll_sentence_20

Once extracted from the protein into a solvent (such as acetone or methanol), these chlorophyll pigments can be separated into chlorophyll a and chlorophyll b. Chlorophyll_sentence_21

The function of the reaction center of chlorophyll is to absorb light energy and transfer it to other parts of the photosystem. Chlorophyll_sentence_22

The absorbed energy of the photon is transferred to an electron in a process called charge separation. Chlorophyll_sentence_23

The removal of the electron from the chlorophyll is an oxidation reaction. Chlorophyll_sentence_24

The chlorophyll donates the high energy electron to a series of molecular intermediates called an electron transport chain. Chlorophyll_sentence_25

The charged reaction center of chlorophyll (P680) is then reduced back to its ground state by accepting an electron stripped from water. Chlorophyll_sentence_26

The electron that reduces P680 ultimately comes from the oxidation of water into O2 and H through several intermediates. Chlorophyll_sentence_27

This reaction is how photosynthetic organisms such as plants produce O2 gas, and is the source for practically all the O2 in Earth's atmosphere. Chlorophyll_sentence_28

Photosystem I typically works in series with Photosystem II; thus the P700 of Photosystem I is usually reduced as it accepts the electron, via many intermediates in the thylakoid membrane, by electrons coming, ultimately, from Photosystem II. Chlorophyll_sentence_29

Electron transfer reactions in the thylakoid membranes are complex, however, and the source of electrons used to reduce P700 can vary. Chlorophyll_sentence_30

The electron flow produced by the reaction center chlorophyll pigments is used to pump H ions across the thylakoid membrane, setting up a chemiosmotic potential used mainly in the production of ATP (stored chemical energy) or to reduce NADP to NADPH. Chlorophyll_sentence_31

NADPH is a universal agent used to reduce CO2 into sugars as well as other biosynthetic reactions. Chlorophyll_sentence_32

Reaction center chlorophyll–protein complexes are capable of directly absorbing light and performing charge separation events without the assistance of other chlorophyll pigments, but the probability of that happening under a given light intensity is small. Chlorophyll_sentence_33

Thus, the other chlorophylls in the photosystem and antenna pigment proteins all cooperatively absorb and funnel light energy to the reaction center. Chlorophyll_sentence_34

Besides chlorophyll a, there are other pigments, called accessory pigments, which occur in these pigment–protein antenna complexes. Chlorophyll_sentence_35

Chemical structure Chlorophyll_section_2

Chlorophylls are numerous in types, but all are defined by the presence of a fifth ring beyond the four pyrrole-like rings. Chlorophyll_sentence_36

Most chlorophylls are classified as chlorins, which are reduced relatives of porphyrins (found in hemoglobin). Chlorophyll_sentence_37

They share a common biosynthetic pathway with porphyrins, including the precursor uroporphyrinogen III. Chlorophyll_sentence_38

Unlike hemes, which feature iron at the center of the tetrapyrrole ring, chlorophylls bind magnesium. Chlorophyll_sentence_39

For the structures depicted in this article, some of the ligands attached to the Mg center are omitted for clarity. Chlorophyll_sentence_40

The chlorin ring can have various side chains, usually including a long phytol chain. Chlorophyll_sentence_41

The most widely distributed form in terrestrial plants is chlorophyll a. Chlorophyll_sentence_42

The structures of chlorophylls are summarized below: Chlorophyll_sentence_43

Chlorophyll_table_general_0

Chlorophyll_cell_0_0_0 Chlorophyll aChlorophyll_header_cell_0_0_1 Chlorophyll bChlorophyll_header_cell_0_0_2 Chlorophyll c1Chlorophyll_header_cell_0_0_3 Chlorophyll c2Chlorophyll_header_cell_0_0_4 Chlorophyll dChlorophyll_header_cell_0_0_5 Chlorophyll fChlorophyll_header_cell_0_0_6
Molecular formulaChlorophyll_header_cell_0_1_0 C55H72O5N4MgChlorophyll_cell_0_1_1 C55H70O6N4MgChlorophyll_cell_0_1_2 C35H30O5N4MgChlorophyll_cell_0_1_3 C35H28O5N4MgChlorophyll_cell_0_1_4 C54H70O6N4MgChlorophyll_cell_0_1_5 C55H70O6N4MgChlorophyll_cell_0_1_6
C2 groupChlorophyll_header_cell_0_2_0 −CH3Chlorophyll_cell_0_2_1 −CH3Chlorophyll_cell_0_2_2 −CH3Chlorophyll_cell_0_2_3 −CH3Chlorophyll_cell_0_2_4 −CH3Chlorophyll_cell_0_2_5 −CHOChlorophyll_cell_0_2_6
C3 groupChlorophyll_header_cell_0_3_0 −CH=CH2Chlorophyll_cell_0_3_1 −CH=CH2Chlorophyll_cell_0_3_2 −CH=CH2Chlorophyll_cell_0_3_3 −CH=CH2Chlorophyll_cell_0_3_4 −CHOChlorophyll_cell_0_3_5 −CH=CH2Chlorophyll_cell_0_3_6
C7 groupChlorophyll_header_cell_0_4_0 −CH3Chlorophyll_cell_0_4_1 −CHOChlorophyll_cell_0_4_2 −CH3Chlorophyll_cell_0_4_3 −CH3Chlorophyll_cell_0_4_4 −CH3Chlorophyll_cell_0_4_5 −CH3Chlorophyll_cell_0_4_6
C8 groupChlorophyll_header_cell_0_5_0 −CH2CH3Chlorophyll_cell_0_5_1 −CH2CH3Chlorophyll_cell_0_5_2 −CH2CH3Chlorophyll_cell_0_5_3 −CH=CH2Chlorophyll_cell_0_5_4 −CH2CH3Chlorophyll_cell_0_5_5 −CH2CH3Chlorophyll_cell_0_5_6
C17 groupChlorophyll_header_cell_0_6_0 −CH2CH2COO−PhytylChlorophyll_cell_0_6_1 −CH2CH2COO−PhytylChlorophyll_cell_0_6_2 −CH=CHCOOHChlorophyll_cell_0_6_3 −CH=CHCOOHChlorophyll_cell_0_6_4 −CH2CH2COO−PhytylChlorophyll_cell_0_6_5 −CH2CH2COO−PhytylChlorophyll_cell_0_6_6
C17−C18 bondChlorophyll_header_cell_0_7_0 Single

(chlorin)Chlorophyll_cell_0_7_1

Single

(chlorin)Chlorophyll_cell_0_7_2

Double

(porphyrin)Chlorophyll_cell_0_7_3

Double

(porphyrin)Chlorophyll_cell_0_7_4

Single

(chlorin)Chlorophyll_cell_0_7_5

Single

(chlorin)Chlorophyll_cell_0_7_6

OccurrenceChlorophyll_header_cell_0_8_0 UniversalChlorophyll_cell_0_8_1 Mostly plantsChlorophyll_cell_0_8_2 Various algaeChlorophyll_cell_0_8_3 Various algaeChlorophyll_cell_0_8_4 CyanobacteriaChlorophyll_cell_0_8_5 CyanobacteriaChlorophyll_cell_0_8_6

Chlorophyll_unordered_list_0

  • Structures of chlorophyllsChlorophyll_item_0_0
  • Chlorophyll_item_0_1
  • Chlorophyll_item_0_2
  • Chlorophyll_item_0_3
  • Chlorophyll_item_0_4
  • Chlorophyll_item_0_5
  • Chlorophyll_item_0_6

Measurement of chlorophyll content Chlorophyll_section_3

Measurement of the absorption of light is complicated by the solvent used to extract the chlorophyll from plant material, which affects the values obtained, Chlorophyll_sentence_44

Chlorophyll_unordered_list_1

  • 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.Chlorophyll_item_1_7
  • The absorption peaks of chlorophyll a are at 465 nm and 665 nm. Chlorophyll a fluoresces at 673 nm (maximum) and 726 nm. The peak molar absorption coefficient of chlorophyll a exceeds 10 M cm, which is among the highest for small-molecule organic compounds.Chlorophyll_item_1_8
  • In 90% acetone-water, the peak absorption wavelengths of chlorophyll a are 430 nm and 664 nm; peaks for chlorophyll b are 460 nm and 647 nm; peaks for chlorophyll c1 are 442 nm and 630 nm; peaks for chlorophyll c2 are 444 nm and 630 nm; peaks for chlorophyll d are 401 nm, 455 nm and 696 nm.Chlorophyll_item_1_9

By measuring the absorption of light in the red and far red regions, it is possible to estimate the concentration of chlorophyll within a leaf. Chlorophyll_sentence_45

Ratio fluorescence emission can be used to measure chlorophyll content. Chlorophyll_sentence_46

By exciting chlorophyll a fluorescence at a lower wavelength, the ratio of chlorophyll fluorescence emission at 705±10 nm and 735±10 nm can provide a linear relationship of chlorophyll content when compared with chemical testing. Chlorophyll_sentence_47

The ratio F735/F700 provided a correlation value of r 0.96 compared with chemical testing in the range from 41 mg m up to 675 mg m. Gitelson also developed a formula for direct readout of chlorophyll content in mg m. The formula provided a reliable method of measuring chlorophyll content from 41 mg m up to 675 mg m with a correlation r value of 0.95. Chlorophyll_sentence_48

Biosynthesis Chlorophyll_section_4

Main article: Chlorophyllide Chlorophyll_sentence_49

In some plants, chlorophyll is derived from glutamate and is synthesised along a branched biosynthetic pathway that is shared with heme and siroheme. Chlorophyll_sentence_50

Chlorophyll synthase is the enzyme that completes the biosynthesis of chlorophyll a by catalysing the reaction EC Chlorophyll_sentence_51

This forms an ester of the carboxylic acid group in chlorophyllide a with the 20-carbon diterpene alcohol phytol. Chlorophyll_sentence_52

Chlorophyll b is made by the same enzyme acting on chlorophyllide b. Chlorophyll_sentence_53

In Angiosperm plants, the later steps in the biosynthetic pathway are light-dependent and such plants are pale (etiolated) if grown in darkness. Chlorophyll_sentence_54

Non-vascular plants and green algae have an additional light-independent enzyme and grow green even in darkness. Chlorophyll_sentence_55

Chlorophyll itself is bound to proteins and can transfer the absorbed energy in the required direction. Chlorophyll_sentence_56

Protochlorophyllide, one of the biosynthetic intermediates, occurs mostly in the free form and, under light conditions, acts as a photosensitizer, forming highly toxic free radicals. Chlorophyll_sentence_57

Hence, plants need an efficient mechanism of regulating the amount of this chlorophyll precursor. Chlorophyll_sentence_58

In angiosperms, this is done at the step of aminolevulinic acid (ALA), one of the intermediate compounds in the biosynthesis pathway. Chlorophyll_sentence_59

Plants that are fed by ALA accumulate high and toxic levels of protochlorophyllide; so do the mutants with a damaged regulatory system. Chlorophyll_sentence_60

Senescence and the chlorophyll cycle Chlorophyll_section_5

The process of plant senescence involves the degradation of chlorophyll: for example the enzyme chlorophyllase (EC ) hydrolyses the phytyl sidechain to reverse the reaction in which chlorophylls are biosynthesised from chlorophyllide a or b. Chlorophyll_sentence_61

Since chlorophyllide a can be converted to chlorophyllide b and the latter can be re-esterified to chlorophyll b, these processes allow cycling between chlorophylls a and b. Chlorophyll_sentence_62

Moreover, chlorophyll b can be directly reduced (via 7-hydroxychlorophyll a) back to chlorophyll a, completing the cycle. Chlorophyll_sentence_63

In later stages of senescence, chlorophyllides are converted to a group of colourless tetrapyrroles known as nonfluorescent chlorophyll catabolites (NCC's) with the general structure: Chlorophyll_sentence_64

Chlorophyll_description_list_2

These compounds have also been identified in ripening fruits and they give characteristic autumn colours to deciduous plants. Chlorophyll_sentence_65

Defective environments can cause chlorosis Chlorophyll_section_6

Further information: Chlorosis Chlorophyll_sentence_66

Chlorosis is a condition in which leaves produce insufficient chlorophyll, turning them yellow. Chlorophyll_sentence_67

Chlorosis can be caused by a nutrient deficiency of iron — called iron chlorosis — or by a shortage of magnesium or nitrogen. Chlorophyll_sentence_68

Soil pH sometimes plays a role in nutrient-caused chlorosis; many plants are adapted to grow in soils with specific pH levels and their ability to absorb nutrients from the soil can be dependent on this. Chlorophyll_sentence_69

Chlorosis can also be caused by pathogens including viruses, bacteria and fungal infections, or sap-sucking insects. Chlorophyll_sentence_70

Complementary light absorbance of anthocyanins Chlorophyll_section_7

Anthocyanins are other plant pigments. Chlorophyll_sentence_71

The absorbance pattern responsible for the red color of anthocyanins may be complementary to that of green chlorophyll in photosynthetically active tissues such as young Quercus coccifera leaves. Chlorophyll_sentence_72

It may protect the leaves from attacks by plant eaters that may be attracted by green color. Chlorophyll_sentence_73

Distribution Chlorophyll_section_8

The chlorophyll maps show milligrams of chlorophyll per cubic meter of seawater each month. Chlorophyll_sentence_74

Places where chlorophyll amounts were very low, indicating very low numbers of phytoplankton, are blue. Chlorophyll_sentence_75

Places where chlorophyll concentrations were high, meaning many phytoplankton were growing, are yellow. Chlorophyll_sentence_76

The observations come from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite. Chlorophyll_sentence_77

Land is dark gray, and places where MODIS could not collect data because of sea ice, polar darkness, or clouds are light gray. Chlorophyll_sentence_78

The highest chlorophyll concentrations, where tiny surface-dwelling ocean plants are thriving, are in cold polar waters or in places where ocean currents bring cold water to the surface, such as around the equator and along the shores of continents. Chlorophyll_sentence_79

It is not the cold water itself that stimulates the phytoplankton. Chlorophyll_sentence_80

Instead, the cool temperatures are often a sign that the water has welled up to the surface from deeper in the ocean, carrying nutrients that have built up over time. Chlorophyll_sentence_81

In polar waters, nutrients accumulate in surface waters during the dark winter months when plants cannot grow. Chlorophyll_sentence_82

When sunlight returns in the spring and summer, the plants flourish in high concentrations. Chlorophyll_sentence_83

Culinary use Chlorophyll_section_9

Synthetic chlorophyll is registered as a food additive colorant, and its E number is E140. Chlorophyll_sentence_84

Chefs use chlorophyll to color a variety of foods and beverages green, such as pasta and spirits. Chlorophyll_sentence_85

Absinthe gains its green color naturally from the chlorophyll introduced through the large variety of herbs used in its production. Chlorophyll_sentence_86

Chlorophyll is not soluble in water, and it is first mixed with a small quantity of vegetable oil to obtain the desired solution. Chlorophyll_sentence_87

Biological use Chlorophyll_section_10

A 2002 study found that "leaves exposed to strong light contained degraded major antenna proteins, unlike those kept in the dark, which is consistent with studies on the illumination of isolated proteins". Chlorophyll_sentence_88

This appeared to the authors as support for the hypothesis that "active oxygen species play a role in vivo" in the short-term behaviour of plants. Chlorophyll_sentence_89

See also Chlorophyll_section_11

Chlorophyll_unordered_list_3


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Chlorophyll.