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 The word chloroplast is derived from the Greek
words chloros, which means green, and plast, which
means form or entity.
 Chloroplasts are organelles found in plant cells and
other eukaryotic organisms that
conduct photosynthesis.
 Chloroplasts are members of a class of organelles
known as plastids.

 Plastids are major organelles found in the cells
of plants and algae. Plastids are the site of
manufacture and storage of important
chemical compounds used by the cell.
 Plastids often contain pigments used in
photosynthesis, and the types of pigments
present can change or determine the cell's
color.

 Chromoplasts - color centers
 There are two main types of chromoplasts -- cartenoids
which store yellow and orange pigment and chlorophyll
which stores green pigment.
 Chloroplasts contain chlorophyll which contains green
pigment and some carotenoids which hold yellow or
orange pigment.
 Chlorophyll traps radiant sun energy then manufactures
complex organic molecules(particularly glucose) from
simple raw organic materials.
 Leucoplasts - energy storage
 Leucoplasts are organelles where starch, oil and protein
are stored.

 These are considered to have originated
from cyanobacteria through endosymbiosis.
 The chloroplast has its own DNA, which codes
for redox proteins involved in electron transport in
photosynthesis. This is called as plastome.
 Chloroplasts are observable as flat discs usually
2-10 μm in diameter and 1-2.5 μm thick.
The chloroplast is contained by an envelope that
consists of an inner and an outer phospholipid
membrane. Between these two layers is the inter
membrane space.

1. outer membrane
2. inter membrane space
3. inner membrane (1,2&3
are envelope)
4. stroma (aqueous fluid)
5. thylakoid lumen (inside
of thylakoid)
6. thylakoid membrane
7. granum (stack of
thylakoids)
8. thylakoid (lamella)
9. starch
10. ribosome
11. plastidial DNA
12. plastoglobule (drop of
lipids)

 The material within the chloroplast is called the stroma and
contains one or more molecules of small circular DNA. It also
contains ribosomes .
 The stacks of sub-organelles present Within the stroma are
thylakoids, which are the site of photosynthesis.
 The thylakoids are arranged in stacks called grana.
 A thylakoid has a flattened disk shape. Inside it is an empty
area called the thylakoid space or lumen.
 Photosynthesis takes place on the thylakoid membrane. It
involves the coupling of cross-
membrane fluxes with biosynthesis via the dissipation of a
proton electrochemical gradient.

Chloroplast contains:  Chlorophyll – green
 Proteins – 35 – 55% pigment – in higher plant,
 Lipids- 20-30%
green algae
 Structure similar to
 Carbohydrates- variable
haem- it contains a
 Chlorophyll- 9% porphyrin ring with
 Carotenoids: 4.5% magnesium
 RNA 3 to 4%  Chlorophyll types:
 DNA 0.5%  Chlorophylla,b,c,d etc.
 Minerals 0.2%  Chlorophyll a , b – higher
 The chloroplast contains plants, green algae
three types of pigments:  Chlorophyll c –
 Chlorophylls dinoflagellates , diatoms
 Carotenoids
and brown algae
 Chlorophyll d –red algae
 Phycobilins

 Thylakoid membranes appear as alternating light-and-dark
bands. Thylakoid membranes appear as alternating light-
and-dark bands, each 0.01 μm thick. Embedded in the
thylakoid membrane are antenna complexes, each of
which consists of the light-absorbing pigments,
including chlorophyll and carotenoids, as well as proteins
that bind the pigments.
 This complex both increases the surface area for light
capture, and allows capture of photons with a wider range
of wavelengths.
 The energy of the incident photons is absorbed by the
pigments and funneled to the reaction centre of this
complex through resonance energy transfer. Two
chlorophyll molecules are then ionised, producing an
excited electron, which then passes onto the
photochemical reaction centre.

 Photosynthesis (photo means “light” and
synthesis means “putting together“ or
"composition") is a process that
converts carbon dioxide , water
into glucose(organic compound), using the
energy from sunlight

 In the light reactions, one molecule of
the pigment chlorophyll absorbs one photon and loses
one electron.
 This electron is passed to a modified form of chlorophyll
called pheophytin, which passes the electron to a quinone
molecule, allowing the start of a flow of electrons down
an electron transport chain that leads to the ultimate reduction
of NADP to NADPH.
 This creates a proton gradient across the chloroplast membrane.
Its dissipation is used by ATP synthase for the synthesis of ATP.
 Photolysis :- The process of breaking of water molecule into H2 &
O2.
2 H2O(l) → O2(g) + 4 H+(aq) + 4e−
 The overall equation for the light-dependent reactions under the
conditions of non-cyclic electron flow in green plants is:
 2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP +
O2

 The two photo system units are Photo system
II(p680) and Photo system I(p700), which have their own
distinct reaction center chlorophylls.
 These pigments are named after the wavelength of their
red-peak absorption maximum. The identity, function and
spectral properties are distinct and determined by each
other and the protein structure surrounding them.
 The function of the reaction center chlorophyll is to use the
energy absorbed by and transferred to it from the other
chlorophyll pigments in the photosystems to undergo a
charge separation, a specific redox reaction in which the
chlorophyll donates an electron into a series of molecular
intermediates called an electron transport chain. The
charged reaction center chlorophyll (P680+) is then
reduced back to its ground state by accepting an electron.

 In Photo system II, the electron that reduces
P680+ ultimately comes from the oxidation of water
into O2 and H+ through several intermediates.
 This reaction is how photosynthetic organisms like
plants produce O2 gas, and is the source for
practically all the O2 in Earth's atmosphere. Photo
system I works in series with Photosystem II, thus the
P700+ of Photo system I is usually reduced, via many
intermediates in the thylakoid membrane, by
electrons ultimately from Photo system II.
 Electron transfer reactions in the thylakoid
membranes are complex, however; and the source
of electrons used to reduce P700+ can vary.

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Choloroplasts

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