3. 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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5. Photosystem Organization
A photosystem consists of
1. 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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6. Photosystem Organization
At 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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7. 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. 8
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 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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10. 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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11. 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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12. 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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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.
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16. 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:
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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
