biochemistry

1. Role of
Pigments in
Photosynthesis
Shreyasha Mishra
MH-IV

2. Role of Pigments
 Pigments are light-absorbing colored
molecules.
 Different pigments absorb different
wavelengths of light, like chlorophylls,
phycobilins, carotenoids.
 Chlorophylls are the major light-absorbing
pigments in plants & act as reaction center.
 They absorb energy from red (650-700nm)
and blue (450nm) light and reflect green light

3. Chloroplast

4. Chlorophylls
In chloroplast,the thylakoids contain
chlorophyll.Chlorophyll is the green pigment
that captures light for photosynthesis
There are various chlorophylls: a,b,c,d,e;
bacteriochlorophyll-a, b, c, d; chlorobium
chlorophylls; bacterioviridin.
Absorption spectra of chlorophyll ranges 670-
673nm.

5. Structure
Chlorophylls are tetrapyrol compounds.
Prophyrin ring present, containing Mg ion
as central atom.
Long hydrophobic isoprenoid chain present in phytol
tail of 20-C atom atteched to IV ring.

6. Accessory Pigments
 Role of Accessory Pigments:
 Accessory pigments help plants
absorb additional light. Plants need
to make these accessory pigments to
maximize the amount of
photosynthesis they can do.
 More pigments = More glucose or
food for the plant!

7. Types of Accessory
Pigments
 Carotenoids: an orange pigment reflect yellow,
orange, and red light.
 Carotenoids give carrots and sweet potatoes their
orange color and are very common
 Phycobilins :- absorbs red, orange, yellow, and
green light.
 Xanthophylls : - a yellow pigment reflect yellow
light.

8. Carotinoids
Carotenoids are red, yellow and orange pigments.Although
specific carotenoids have been identified in photosynthetic
centers in plants Carotenoids absorb light in the 400-500 nm
region of the visible spectrum. This physical property imparts
the characteristic red/yellow color of the pigments.
Carotenoids contain a conjugated backbone composed of
isoprene units, which are usually inverted at the center of the
molecule, imparting symmetry. There are two general classes
of carotenoids: carotenes and xanthophylls. Carotenes consist
only of carbon and hydrogen atoms; beta-carotene is the most
common carotene. Xanthophylls have one or more oxygen
atoms; lutein is one of the most common xanthophylls.

9. Xanthophylls
 Xanthophylls (originally phylloxanthins) are
yellow pigments that occur widely in nature and form one of
two major divisions of the carotenoid group; the other
division is formed by the carotenes.
 The molecular structure of xanthophylls is similar to that
of carotenes, but xanthophylls contain oxygen atoms,
while carotenes are purely hydrocarbons with no oxygen
 Xanthophylls contain their oxygen either as hydroxyl
groups and/or as pairs of hydrogen atoms that are substituted
by oxygen atoms acting as a bridge .

10. Phycobilins
 Phycobilins meaning "alga“, bilis meaning "bile" are light-
capturing bilins found in cyanobacteria and in
the chloroplasts of red algae, glaucophytes and
some cryptomonads (though not in green algae and plants).
 phycobilins consist of an open chain of four pyrrole rings
(tetrapyrrole) and are structurally similar to
the bile pigment bilirubin.
 Phycobilins are also closely related to the chromophores of the
light-detecting plant pigment phytochrome, which also consist of
an open chain of four pyrroles. Chlorophylls are composed of four
pyrroles as well, but there the pyrroles are arranged in a ring and
contain a metal atom in the center of it.