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Hafiz Muhammad Athar Rizwan

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  1. 1. University Of Gujrat (UOG) 06-04-2012 1
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  3. 3. Chlorophyll:Greenish pigment containing a porphyrin ring. Stablering-shaped molecule around which electrons are free tomigrate.Chlorophyll is the molecule that traps this most elusiveof all powers - and is called a photoreceptor. It is foundin the chloroplasts of green plants, and is what makesgreen plants, green. 3
  4. 4. Light & Chlorophyll 6CO2 + 6H2O C6H12O6 + 6O2Carbon dioxide +Water Glucose + Oxygen 4
  5. 5. Photosystem OrganizationA photosystem consists of1. an antenna complex (light harvesting complex) of hundreds of accessory pigment molecules that gather photons and feeds energy to reaaction center2. a reaction center of one or more chlorophyll a molecules pass electrons out of photosystem (photochemical reactions)In summary, energy of electrons is transferred through the antenna complex to the reaction center. 5
  6. 6. Photosystem OrganizationAt the reaction center (transmembrane protein complex), the energy from the antenna complex is transferred to chlorophyll a.This energy causes an electron from chlorophyll to become excited.The excited electron is transferred from chlorophyll a to an electron acceptor.Water donates an electron to chlorophyll a to replace the excited electron. 6
  7. 7. Chlorophyll “a”:This is the molecule which makes photosynthesis possible, bypassing its energized electrons on to molecules which willmanufacture sugars. All plants, algae, and cyanobacteriawhich photosynthesize contain chlorophyll "a".Chlorophyll "b“:It occurs only in "green algae" and in the plants.The small difference in one of the side chains allows each typeof chlorophyll to absorb light at slightly differentwavelengths.Chlorophyll "c“:Found only in the photosynthetic members of the Chromistaas well as the dinoflagellates. 8
  8. 8. chlorophyll consists ofphytol protoporphryin ring, alcohol (phytol) and Mg2+ 9
  9. 9. In the first phase of chlorophyll biosynthesis:The amino acid glutamic acid is converted to 5-aminolevulinic acid (ALA) .This reaction is unusual in that it involves acovalent intermediate in which the glutamic acidis attached to a transfer RNA molecule. This isone of a very small number of examples inbiochemistry in which a tRNA is utilized in aprocess other than protein synthesis.Two molecules of ALA are then condensed toform porphobilinogen (PBG), which ultimatelyform the pyrrole rings in chlorophyll. 10
  10. 10.  The next phase is the assembly of a porphyrinstructure from four molecules of PBG. This phase consists of six distinct enzymatic steps,ending with the product protoporphyrin IX. 11
  11. 11. All the biosynthesis steps up to this point are thesame for the synthesis of both chlorophyll andheme .But here the pathway branches, and the fate of themolecule depends on which metal is inserted intothe center of the porphyrin.If magnesium is inserted by an enzyme calledmagnesium chelatase, then the additional stepsneeded to convert the molecule into chlorophyll takeplace; if iron is inserted, the species ultimatelybecomes heme. 12
  12. 12. The next phase of the chlorophyll biosynthetic pathway isthe formation of the fifth ring (ring E) by cyclization ofone of the propionic acid side chains to formprotochlorophyllide.The pathway involves the reduction of one of the doublebonds in ring D, using NADPH.This process is driven by light in angiosperms and iscarried out by an enzyme called protochlorophyllideoxidoreductase (POR). 13
  13. 13. ChlorophyllBiosynthesis 14
  14. 14. Chlorophyll Biosynthesis 15
  15. 15. Control of chlorophyll synthesis :– ALA synthetase is the rate limiting step in the process , ALA synthetase is inducible enzyme ( Photo inducible ) i.e. formation of this enzyme increase in light.– Enzymes From ALA to protoporphyrin are constitutive (not induced) i. e. conc .remain fairly constant and not regulated .– Some kind of RNA synthesis is required for large scale production of chlorophyll. 16
  16. 16. Chlorophyll is often called the blood of plants because it isremarkably similar molecular structure to our own blood. Ithas the same pH as that of healthy blood. It also functionssimilarly by releasing oxygen into the air just as hemoglobinreleases human oxygen into human tissue. In the 1930s and40s when scientists discovered these similarities, theysuspected that chlorophyll might be able to regeneratehuman blood. So, they conducted extensive medicalstudies, which demonstrated that chlorophyll did indeedhelp: 1.Build healthy blood 2.Improve circulation 3.Cleanse the organs and gastrointestinal tract. 4.Heal gum disease and ulcers 5.Create an unfavorable environment for bacteria 6.Freshen the breath and neutralize body odors 17
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