Chlorophyll a

Source: Wikipedia, the free encyclopedia.
Chlorophyll a
Structure of chlorophyll a
Names
IUPAC name
Chlorophyll a
Systematic IUPAC name
Magnesium [methyl (3S,4S,21R)-14-ethyl-4,8,13,18-tetramethyl-20-oxo-3-(3-oxo-3-{[(2E,7R,11R)-3,7,11,15-tetramethyl-2-hexadecen-1-yl]oxy}propyl)-9-vinyl-21-phorbinecarboxylatato(2−)-κ2N,N′]
Other names
α-Chlorophyll
Identifiers
3D model (
JSmol
)
ChemSpider
ECHA InfoCard
 100.006.852 Edit this at Wikidata
EC Number
  • 207-536-6
RTECS number
  • FW6420000
UNII
  • InChI=1S/C55H73N4O5.Mg/c1-13-39-35(8)42-28-44-37(10)41(24-25-48(60)64-27-26-34(7)23-17-22-33(6)21-16-20-32(5)19-15-18-31(3)4)52(58-44)50-51(55(62)63-12)54(61)49-38(11)45(59-53(49)50)30-47-40(14-2)36(9)43(57-47)29-46(39)56-42;/h13,26,28-33,37,41,51H,1,14-25,27H2,2-12H3,(H-,56,57,58,59,61);/q-1;+2/p-1/b34-26+;/t32-,33-,37+,41+,51-;/m1./s1 checkY
    Key: ATNHDLDRLWWWCB-AENOIHSZSA-M checkY
  • InChI=1S/C55H73N4O5.Mg/c1-13-39-35(8)42-28-44-37(10)41(24-25-48(60)64-27-26-34(7)23-17-22-33(6)21-16-20-32(5)19-15-18-31(3)4)52(58-44)50-51(55(62)63-12)54(61)49-38(11)45(59-53(49)50)30-47-40(14-2)36(9)43(57-47)29-46(39)56-42;/h13,26,28-33,37,41,51H,1,14-25,27H2,2-12H3,(H-,56,57,58,59,61);/q-1;+2/p-1/b34-26+;/t32?,33?,37-,41-,51+;/m0./s1
    Key: ATNHDLDRLWWWCB-WJQLOWBJSA-M
  • CCC1=C(C2=NC1=CC3=C(C4=C([N-]3)C(=C5[C@H]([C@@H](C(=N5)C=C6C(=C(C(=C2)[N-]6)C=C)C)C)CCC(=O)OC/C=C(\C)/CCCC(C)CCCC(C)CCCC(C)C)[C@H](C4=O)C(=O)OC)C)C.[Mg+2]
  • COC(=O)C9C(=O)c6c(C)c3N7c6c9c2C(CCC(=O)COCC=C(C)CCCC(C)CCCC(C)CCCC(C)C)C(C)c1cc5N8c(cc4n([Mg]78n12)c(c=3)c(CC)c4c)c(C=C)c5C
Properties
C55H72MgN4O5
Molar mass 893.509 g·mol−1
Appearance Green
Odor Odorless
Density 1.079 g/cm3[1]
Melting point ~ 152.3 °C (306.1 °F; 425.4 K)[2]
decomposes[1]
Insoluble
Solubility Very soluble in ethanol, ether
Soluble in ligroin,[2] acetone, benzene, chloroform[1]
Absorbance See text
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Chlorophyll a is a specific form of

reaction center where specific chlorophylls P680 and P700 are located.[6]

Distribution of chlorophyll a

Chlorophyll a is essential for most

photoautotroph.[7] These organisms use bacteriochlorophyll and some chlorophyll a but do not produce oxygen.[7] Anoxygenic photosynthesis is the term applied to this process, unlike oxygenic photosynthesis where oxygen is produced during the light reactions of photosynthesis
.

Molecular structure

The molecular structure of chlorophyll a consists of a

side chains and a hydrocarbon tail formed by a phytol ester
.

Structure of chlorophyll a molecule showing the phytol tail

Chlorin ring

Chlorin, the central ring structure of the chlorophyll a

Chlorophyll a contains a magnesium ion encased in a large ring structure known as a chlorin. The chlorin ring is a heterocyclic compound derived from pyrrole. Four nitrogen atoms from the chlorin surround and bind the magnesium atom. The magnesium center uniquely defines the structure as a chlorophyll molecule.[8] The porphyrin ring of bacteriochlorophyll is saturated, and lacking alternation of double and single bonds causing variation in absorption of light.[9]

Side chains

The green boxed CH3 is the methyl group at the C-7 position chlorophyll a

Side chains are attached to the chlorin ring of the various chlorophyll molecules. Different side chains characterize each type of chlorophyll molecule, and alters the absorption spectrum of light.[10]
[11] For instance, the only difference between chlorophyll a and chlorophyll b is that chlorophyll b has an aldehyde instead of a methyl group at the C-7 position.[11]

Hydrocarbon tail

The phytol ester of chlorophyll a (R in the diagram) is a long

thylakoid membrane of the chloroplast.[5] Once detached from the porphyrin ring, phytol becomes the precursor of two biomarkers, pristane and phytane, which are important in the study of geochemistry and the determination of petroleum sources.[12]

Biosynthesis

Main article: Chlorophyllide

The Chlorophyll a

glutamate and is synthesised along a branched pathway that is shared with heme and siroheme.[14][15][16]
The initial steps incorporate glutamic acid into
protoporphyrin IX.[8]

Chlorophyll synthase[17] is the enzyme that completes the biosynthesis of chlorophyll a[18][19] by catalysing the reaction EC 2.5.1.62

chlorophyllide a + phytyl diphosphate chlorophyll a + diphosphate

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

Reactions of photosynthesis

Absorbance of light

Light spectrum

Absorption spectrum of chlorophyll a and chlorophyll b. The use of both together enhances the size of the absorption of light for producing energy.

Chlorophyll a absorbs light within the violet, blue and red wavelengths. Accessory photosynthetic pigments broaden the spectrum of light absorbed, increasing the range of wavelengths that can be used in photosynthesis.[5] The addition of chlorophyll b next to chlorophyll a extends the absorption spectrum. In low light conditions, plants produce a greater ratio of chlorophyll b to chlorophyll a molecules, increasing photosynthetic yield.[10]

Light gathering

The antenna complex with energy transfer within the thylakoid membrane of a chloroplast. Chlorophyll a in the reaction center is the only pigment to pass boosted electrons to an acceptor (modified from 2).

Absorption of light by photosynthetic pigments converts photons into chemical energy. Light energy radiating onto the chloroplast strikes the pigments in the thylakoid membrane and excites their electrons. Since the chlorophyll a molecules only capture certain wavelengths, organisms may use accessory pigments to capture a wider range of light energy shown as the yellow circles.[6] It then transfers captured light from one pigment to the next as resonance energy, passing energy one pigment to the other until reaching the special chlorophyll a molecules in the reaction center.[10] These special chlorophyll a molecules are located in both photosystem II and photosystem I. They are known as P680 for Photosystem II and P700 for Photosystem I.[20] P680 and P700 are the primary electron donors to the electron transport chain. These two systems are different in their redox potentials for one-electron oxidation. The Em for P700 is approximately 500mV, while the Em for P680 is approximately 1,100-1,200 mV.[20]

Primary electron donation

Chlorophyll a is very important in the energy phase of photosynthesis. Two

electrons need to be passed to an electron acceptor for the process of photosynthesis to proceed.[5] Within the reaction centers of both photosystems there are a pair of chlorophyll a molecules that pass electrons on to the transport chain through redox reactions.[20]

Ocean

The concentration of chlorophyll A is used as an index of phytoplankton biomass. In the ocean, phytoplankton all contain the chlorophyll pigment, which has a greenish color.

Phytoplankton are microscopic organisms that live in watery environments and changes in the amount of phytoplankton indicate the change in productivity of the ocean. Phytoplankton can be affected indirectly by climatic factors, such as changes in water temperatures and surface winds.[21]

See also

  • Photosystem II light harvesting protein
  • Chlorophyll b, another related chemical
  • Chlorophyll c, an accessory pigment of chlorophyll

References

  1. ^ a b c Anatolievich KR. "Chlorophyll a". chemister.ru. Archived from the original on 2014-11-29. Retrieved 2014-08-23.
  2. ^
    ISBN 978-1-4200-9084-0
    .
  3. ^ "Photosynthesis". Archived from the original on 2009-11-28.
  4. doi:10.1080/00219266.2020.1858930
    .
  5. ^ a b c d e Raven PH, Evert RF, Eichhorn SE (2005). "Photosynthesis, Light, and Life". Biology of Plants (7th ed.). W. H. Freeman. pp. 119–127.
    ISBN 0-7167-9811-5
    .
  6. ^ a b Papageorgiou G, Govindjee (2004). Chlorophyll a Fluorescence, A Signature of Photosynthesis. Advances in Photosynthesis and Respiration. Vol. 19. Springer. p. 14, 48, 86.
  7. ^ a b Eisen JA, Nelson KE, Paulsen IT, Heidelberg JF, Wu M, Dodson RJ, et al. (July 2002). "The complete genome sequence of Chlorobium tepidum TLS, a photosynthetic, anaerobic, green-sulfur bacterium". Proceedings of the National Academy of Sciences of the United States of America. 99 (14): 9509–14.
    PMID 12093901
    .
  8. ^
    ISBN 0-87893-856-7. Archived from the original
    on 2020-08-07. Retrieved 2010-05-05.
  9. ^ Campbell MK, Farrell SO (20 November 2007). Biochemistry (6th ed.). Cengage Learning. p. 647.
    ISBN 978-0-495-39041-1
    .
  10. ^ a b c Lange L, Nobel P, Osmond C, Ziegler H (1981). Physiological Plant Ecology I – Responses to the Physical Environment. Vol. 12A. Springer-Verlag. pp. 67, 259.
  11. ^ a b Niedzwiedzki DM,
    S2CID 28352285
    .
  12. S2CID 128737515
    .
  13. PMID 9442890
    .
  14. PMID 11152419
    .
  15. PMID 7842850
    .
  16. PMID 12828371
    .
  17. S2CID 3099209
    .
  18. S2CID 21174896
    .
  19. S2CID 23808539
    .
  20. ^ a b c Ishikita H, Saenger W, Biesiadka J, Loll B, Knapp EW (June 2006). "How photosynthetic reaction centers control oxidation power in chlorophyll pairs P680, P700, and P870". Proceedings of the National Academy of Sciences of the United States of America. 103 (26): 9855–60.
    PMID 16788069
    .
  21. ^ "Nauru Environment Data Portal | Environmental Information for Decision Making". nauru-data.sprep.org. Retrieved 2024-01-27.

External links

Retrieved from "https://en.wikipedia.org/w/index.php?title=Chlorophyll_a&oldid=1210805594"