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Hafiz Muhammad Athar RizwanBS Chemistry03336256150

University Of Gujrat (UOG)06-04-2012

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Chlorophyll

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Chlorophyll: Greenish pigment containing a porphyrin ring. Stable ring-shaped molecule around which electrons are free to migrate.Chlorophyll is the molecule that traps this 'most elusive of all powers' - and is called a photoreceptor. It is found in the chloroplasts of green plants, and is what makes green plants, green.

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It is capable of channelling the energy of sunlight into chemical energy through the process of photosynthesis. In photosynthesis, the energy absorbed by chlorophyll transforms carbon dioxide and water into carbohydrates and oxygen.CO2 + H2O (CH2O) + O2

Carbon dioxide +Water Glucose + Oxygen

6CO2 + 6H2O C6H12O6 + 6O2

Light & Chlorophyll

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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 center

2. 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.

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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.

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Kinds of Chlorophyll:Chlorophyll “a”:This is the molecule which makes photosynthesis possible, by passing its energized electrons on to molecules which will manufacture sugars. All plants, algae, and cyanobacteria which 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 type of chlorophyll to absorb light at slightly different wavelengths.Chlorophyll "c“:Found only in the photosynthetic members of the Chromista as well as the dinoflagellates.

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chlorophyllconsists of

phytol protoporphryinring, alcohol(phytol) andMg2+

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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 a covalent intermediate in which the glutamic acid is attached to a transfer RNA molecule. This is one of a very small number of examples in biochemistry in which a tRNA is utilized in a process other than protein synthesis.Two molecules of ALA are then condensed to form porphobilinogen (PBG), which ultimately form the pyrrole rings in chlorophyll.

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The next phase is the assembly of a porphyrin structure from four molecules of PBG.

This phase consists of six distinct enzymatic steps, ending with the product protoporphyrin IX.

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All the biosynthesis steps up to this point are the same for the synthesis of both chlorophyll and heme .

But here the pathway branches, and the fate of the molecule depends on which metal is inserted into the center of the porphyrin.

If magnesium is inserted by an enzyme called magnesium chelatase, then the additional steps needed to convert the molecule into chlorophyll take place; if iron is inserted, the species ultimately becomes heme.

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The next phase of the chlorophyll biosynthetic pathway is the formation of the fifth ring (ring E) by cyclization of one of the propionic acid side chains to form protochlorophyllide.

The pathway involves the reduction of one of the double bonds in ring D, using NADPH.

This process is driven by light in angiosperms and is carried out by an enzyme called protochlorophyllide oxidoreductase (POR).

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Chlorophyll Biosynthesis

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Chlorophyll Biosynthesis

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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 (notinduced) i. e. conc .remain fairly constant and notregulated .

– Some kind of RNA synthesis is required for large scaleproduction of chlorophyll.

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Chlorophyll is often called the blood of plants because it is remarkably similar molecular structure to our own blood.  It has the same pH as that of healthy blood.  It also functions similarly by releasing oxygen into the air just as hemoglobin releases human oxygen into human tissue.  In the 1930s and 40s when scientists discovered these similarities, they suspected that chlorophyll might be able to regenerate human blood.  So, they conducted extensive medical studies, which demonstrated that chlorophyll did indeed help:

 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

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The END