Page 7 - 11-Bio-11 Kingdom plantae

11. Bioenergetics eLearn.Punjab

A chlorophyll molecule has two Fig. 11.2 A molecule of chlorophyll
main parts : One flat, square,
light absorbing hydrophilic head 7 V: 1.1
and the other long, anchoring,
hydrophobic hydrocarbon tail.
The head is complex porphyrin
ring which is made up of 4 joined
smaller pyrrole rings composed
of carbon and nitrogen atoms. An
atom of magnesium is present in
the centre of porphyrin ring and is
coordinated with the nitrogen of
each pyrrole ring (Fig. 11.2) That is
why magnesium deficiency causes
yellowing in plants.

Haem portion of haemoglobin
is also a porphyrin ring but
containing an ironatom instead of
magnesium atom in the centre.

Long hydrocarbon tail which is
attached to one of the pyrrole rings
is phytol (C20 H39). The chlorophyll
molecule is embedded in the
hydrophobic core of thylakoid
membrane by this tail.

Chlorophyll a and chlorophyll b
differ from each other in only one
of the functional groups bonded
to the porphyrin; the methyl group
(-CH3 ) in chlorophyll a is replaced
by a terminal carbonyl group
(-CHO) in chlorophyll b.