Role of Pigments in Photosynthesis

biochemistry

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

2. Role of Pigments
Pigmentsare light-absorbing colored
molecules.
Different pigments absorb different
wavelengths of light, like chlorophylls,
phycobilins, carotenoids.
Chlorophyllsare the major light-absorbing
pigments in plants & act as reaction center.
They absorb energy fromred(650-700nm)
and blue(450nm) light and reflect greenlight
in visible region, giving plants their green

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 tetrapyrolcompounds.
Prophyrinring present, containing Mgion
as central atom.
Long hydrophobic isoprenoidchain present in phytol
tail of 20-C atom attechedto 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(originallyphylloxanthins) are
yellowpigmentsthat occur widely in nature and form one of
two major divisions of thecarotenoidgroup; the other
division is formed by thecarotenes.
The molecular structure of xanthophylls is similar to that
ofcarotenes, but xanthophylls containoxygenatoms,
whilecarotenesare purely hydrocarbons with no oxygen
Xanthophylls contain their oxygen either ashydroxyl
groupsand/or as pairs of hydrogen atoms that are substituted
by oxygen atoms acting as a bridge .

10. Phycobilins
Phycobilinsmeaning "alga“,bilismeaning "bile" arelight-
capturingbilinsfound incyanobacteriaand in
thechloroplastsofred algae,glaucophytesand
somecryptomonads(though not ingreen algaeandplants).
phycobilins consist of an open chain of fourpyrrolerings
(tetrapyrrole) and are structurally similar to
thebilepigmentbilirubin.
Phycobilins are also closely related to the chromophores of the
light-detecting plant pigmentphytochrome, which also consist of
an open chain of four pyrroles.Chlorophyllsare 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.