- Chloroplasts are organelles found in plant cells and algae that conduct photosynthesis. They contain chlorophyll and have a double membrane structure. - The inner membranes of chloroplasts form sac-like structures called thylakoids, which contain the pigments and proteins involved in the light-dependent reactions of photosynthesis. These reactions trap light energy from the sun and use it to convert water to oxygen and produce ATP and NADPH. - The products of the light reactions, ATP and NADPH, are used in the light-independent Calvin cycle which occurs in the chloroplast stroma. The Calvin cycle converts carbon dioxide into glucose using the energy from ATP and NADPH.

1. CHLOROPLAST
AND LIGHT
REACTION
PRESENTED BY –
ARCHANA KUMARI SHAW
ROLL NO.:02
M.Sc1st YEAR BIOTECHNOLOGY

2. Pioneers in chloroplast & plant
molecular biology
Discovered chloroplast
genetics (Chlamydomonas)
andDNA
Chloroplastgenes in corn;
demonstratedlight regulation
Chloroplastgene
function;nuclear control
Ruth Sager Lawrence Bogorad Jean-David
Rochaix
(Harvard) (Harvard) (Geneva)

3. THE HOUSE OF PLANT PHOTOSYNTHETIC MACHINERY-
CHLOROPLAST

4. INTRODUCTION
→ The term Chloroplast was first described
by Nehemiah Grew and Antonie Van
Leeuwenhoek.
→ “Chloro” means green while “ Plast”
meansliving.
→ Chlorophyll pigments present in the
chloroplast imparts the greencolour to plants.
→ Chloroplasts are present in plants and
other eukaryotic organisms that conducts
photosynthesis.
→ Chloroplasts are the most important
plastids found in plant cells.
Photo of Chloroplast in a
Moss Cell

5. ORIGIN AND EVOLUTION

6. BIOGENESIS OF CHLOROPLAST

7. CHLOROPLAST
 Also known as the site of Photosynthesis. We all know what photosynthesis is, it is the process by
which chlorophyll containing cell synthesize carbohydrate from CO2 & H2O using the energy of
sunlight.
 The green leaves are the main photosynthetic organ and chloroplast are the organelles which
function as the site of photosynthesis in higher plants.
 Within the chloroplast there is a membranous system consisting of grana and stromal lamellae
and fluid matrix.
 The membrane system is responsible for trapping light energy and synthesizing ATP and NADPH.
 In Stroma the enzymatic reaction incorporates CO2 in the plant leading to the synthesis of sugar.
 The former set of reaction are light dependent and are light reaction. The latter reaction though
dependent on the product of light i.e., ATP and NADPH can occur in dark and are called dark
reaction.
 A typical plant cell mightcontain about 50 chloroplasts per cell.

8.  Chloroplasts found in higher plants are generally biconvex or planoconvex shaped. In different
plants chloroplasts have different shapes, they vary from spheroid, filamentous saucer-shaped,
discoid or ovoid shaped.
 They are vesicular and have a colorless center. Some chloroplasts are in shape of club, they have a
thin middle zone and the ends are filled with chlorophyll. In algae a single huge chloroplast is seen
that appears as a network, a spiral band or a stellate plate.
 The size of the chloroplast also varies from species to species and it is constant for a given cell type.
In higher plants, the average size of chloroplast is 4-6 µm in diameter and 1-3µm in thickness.
 Chloroplasts are bigger and fatter than mitochondria. That is why chloroplasts settle first when
photosynthetic cells are homogenized and centrifuged.
 Like mitochondria, chloroplasts have their own DNA, termed cpDNA.
 Site of photosynthesis in plants and algae.
CO2 + H2O + Sun Light ----->Sugar+ O2
Structure of Chloroplast

10.  The chloroplast are double membrane bound organelles and are
the site of photosynthesis The chloroplasts have a system of
three membranes: the outer membrane, the inner membrane and
the thylakoid system. The outer and the inner membrane of the
chloroplast enclose a semi-gel-like fluid known as the stroma.
This stroma makes up much of the volume of the chloroplast,
the thylakoids system floats in the stroma.
 Outer membrane - It is a semi-porous membrane and is
permeable to small molecules and ions, which diffuses easily.
The outer membrane is not permeable to larger proteins.
 Intermembrane Space - It is usually a thin intermembrane space
about 10-20 nanometers and it is present between the outer and
the inner membrane of the chloroplast.
 Inner membrane - The inner membrane of the chloroplast forms
a border to the stroma. It regulates passage of materials in and
out of the chloroplast. In addition of regulation activity, the fatty
acids, lipids and carotenoids are synthesized in the inner
chloroplast membrane.

11.  STROMA: is a alkaline, aqueous fluid which is protein rich and
is present within the inner membrane of the chloroplast. The
space outside the thylakoid space is called the stroma. The
chloroplast DNA chlroplast ribosomes and the thylakoid
sytem, starch granules and many proteins are found floating
aroundthestroma.
 THYLAKOID: The thylakoid system is suspended in the
stroma. The thylakoid system is a collection of membranous
sacks called thylakoids. The chlorophyll is found in the
thylakoids and is the sight for the process of light reactions of
photosynthesis to happen. The thylakoids are arranged in
stacksknownasgrana.
 Eachgranumcontainsaround10-20thylakoids.
 Thylakoids are interconnected small sacks, the membranes of
these thylakoids is the site for the light reactions of the
photosynthesis to take place. The word 'thylakoid' is derived
from the Greek word "thylakos" which means 'sack'.

12.  Protein complexes which carryoutlight reactionof photosynthesisare embedded inthe membranes of
the thylakoids.The PhotosystemIandthePhotosystemII are complexes thatharvest light with
chlorophyllandcarotenoids,they absorbthe light energy anduse it to energize the electrons.
 The molecules present in thethylakoidmembraneuse theelectronsthatareenergized topumphydrogen
ions intothe thylakoidspace,this decrease thepHand become acidicinnature.Alargeprotein complex
knownas theATPsynthasecontrols theconcentrationgradientofthe hydrogenions inthe thylakoid
spaceto generateATP energy andthe hydrogenions flowbackintothe stroma.
 Thylakoidsareof twotypes-granalthylakoidsandstromalthylakoids.Granalthylakoidsarearrangedin
the granaare pancakeshapedcircular discs,which areabout300-600nanometers in diameter. The
stromalthylakoidsarein contactwiththe stromaandare in theform ofhelicoid sheets.
The granalthylakoidscontainonly photosystemIIprotein complex, this allows them tostacktightlyand
formmany granallayers wiht granalmembrane. This structureincreases stabilityandsurface areaforthe
captureof light.
 The photosystemIandATPsynthaseprotein complexes are present in thestroma.These protein
complexes acts asspacers between the sheets ofstromalthylakoids.

13. Outer membrane
Permeable
Inner membrane
Selectively permeable
Transport proteins present
Ribosome (70S)
Site of protein synthesis
Intermembrane space
Circular DNA
Codes for proteins (enzymes)
- e.g. rubisco
Intergranal lamella
Granum
Stack of thylakoids (~ 100)
Large surface area
Site of light-depemdent reactions
Products – ATP + reduced NADP + O2
Stroma (fluid)
Enzymes for light-independent
(dark) reactions – Calvin cycle
Products – glucose + NADP + ADP
Starch grain (storage)
Storage polysaccharide (made of
glucose)Thylakoid membrane
• Increase surface area
• Pigments arranged in clusters
termed photosystems (PS)
• Allow maximum absorption of
light
• Electron carriers present
• Proton pumps present
• ATP synthase complex (for
ATP synthesis by
photophosphorylation)
• Photolysis (splitting) of water
• Products of light-dependant
reactions (ATP + reduced
NADP + O2) pass into stroma
Biconvex shape
Increases surface area
Lipid droplet
CHLOROPLAST

14. Chloroplasts Trap Solar Energy and Convert
it to Chemical Energy
 The purpose of the chloroplast is to make sugars
that feed the cell’s machinery. Photosynthesis is
the process of a plant taking energy from the Sun
and creating sugars. When the energy from the
Sun hits a chloroplast and the chlorophyll
molecules, light energy is converted into the
chemical energy found in compounds such
as ATPandNADPH.
 Those energy-rich compounds move into the
stroma where enzymes fix the carbon atoms from
carbon dioxide (CO2). The molecular reactions
eventually create sugar and oxygen (O2). Plants
and animals then use the sugars (glucose) for food
and energy. Animals also breathe the oxygen gas
thatis released.

15. Functionsof chloroplast:
 Inplantsall thecells participateinplantimmune response asthey lack specialized immune cells. The
chloroplastswith the nucleus andcellmembrane andER arethe key organelles of pathogendefense.
 The most importantfunctionofchloroplastis tomake foodbythe process of photosynthesis.Foodis
preparedin theformof sugars.During the process ofphotosynthesissugarandoxygen aremade
using lightenergy, water,and carbondioxide.
 Lightreactionstakes place onthe membranes of thethylakoids.
 Chloroplasts,like the mitochondriause thepotentialenergyof theH+ions orthe hydrogenion
gradienttogenerate energy inthe formof ATP.
 The darkreactionsalso knownas theCalvin cycletakes place in the stromaof chloroplast.
 ProductionofNADPH2 molecules and oxygenas a result ofphotolysisof water.
 BY theutilizationof assimilatorypowers the6-carbonatomis brokenintotwomolecules of
phosphoglycericacid.

17. LIGHT REACTION
What is the main purpose of the light reactions?
 Input: Water, Photons of light
 Output: Oxygen, ATP & NADPH

18. PhotosyntheticPigment
 They are the substances that have an ability to absorb light at a
specific wavelength. There are four types of pigments:
 1) Chlorophyll- a 2) Chlorophyll- b
3) Carotenes & 4) Xanthophyll.
 The chloroplast pigments are broadly classified into two types: -
1) Chlorophyll - They are the green photosynthetic pigment.
 A series of 5 types of chlorophyll i.e., chlorophyll a, b, c, d & e
occurs in plants other than bacteriochlorophyll.
 Chlorophyll a found in all photosynthesis organism except bacteria
hence, it is known as Universal photosynthetic pigments.
 Chlorophyll b and other chloroplast pigments are known as
accessory pigment. As they transfer the absorbed light energy to
chlorophyll a.
2) Carotenoids - It absorbs blue light and reflects yellow (xanthophyll)
and orange (carotene) light. They absorb light by chlorophylls – then
pass .

19. PIGMENT SYSTEM
Photosystem I (PS – I): It is a protein complex that uses light to mediate electron
transfer.
 It lies on the outer surface of thylakoids and more of chlorophyll-a molecule
(P – 700).
 Here, P stands for Pigment and 700 is the wavelength of light at which the
molecule absorb.
Photosystem II (PS – II): It is a pigment protein complex consisting of several
proteins and cofactors.
 It occurs on the inner surface of thylakoids and have chlorophyll a,
chlorophyll b, carotenoids. Carotenoids content is higher as compared to PS
I.
 PS – II has a special type of chlorophyll a molecule called P – 680.

20. LIGHT REACTION IN PHOTOSYNTHESIS
 Photosynthesis is two step process in which one step is light dependent and the
other is independent.
 The light reaction , a light independent reaction which occur in the grana of
chloroplast, and require the direct energy of light to make NADPH and ATP that
are used in dark reaction.
 The photochemical reaction occurs in the light reaction- in this phase the solar
energy is trapped by chlorophyll stored in the form of chemical energy of ATP
and as reducing powerNADPH2. The ATP and NADPH2 together constitute the
assimilatory power of plant. O2 is exhaled in light reacts by splitting water
molecules.
 Light reaction in the photosystem starts electron flow . In oxygenic
photosynthetic organisms, flow of electron is of two types: Cyclic and Non-
Cyclic.

21. Non – Cyclic Electron flow:
 It is a light- induced electron transport from water to NADP+ and a concomitant evolution of oxygen.
It involves a collaboration of two photosystems: PSII and PSI. Electron move form water through PSII
and PSI and thentoNADP+.
 Electron transport leads to generation of proton- motive force and synthesis of ATP. Formation of
ATP dueto lightinducednon-cyclicelectronflow iscalled Non-cyclic Phosphorylation.
 Electronsreleasedduringphotolysisof water ispicked by thephotocenterof PSII calledP680.
 It passes through a series of e- carrier (Phe) Phephytin, Plastoquinone (Pq), Cytochrome (B12),
Plastocyanine(PC).
 By passing over to Cytohrome complex, the electrons loses sufficient energy for the synthesis of ATP.
Theelectronishanded overtothephotocenter(P700).
 P700 excludes the electron passes through special chlorophyll molecule Fe- S complex, Ferrodoxine
to finally reach NADPH+. The later, combine with H+ with the help of NADP reductase to form
NADPH.Thisiscalled Z-scheme dueto Zig-Zag shape.

22. Z-Scheme(Non-cyclic flow of electrons)

23. Cyclic Electron flow:
 It is the process of photophosphorylation in which the electrons are expelled by the excited photo-
center is to it after passing through a series of electron carrier. It involves PSI only.
 When non-cyclic phosphorylation is stopped under certain condition, cyclic photophosphorylation
occurs. The non-cyclic process can be stopped by illuminating isolated chloroplast with a lighter
wavelength greater than 680nm actives.
 In cyclic electron flow , photo-excited electrons from P700 of PSI move through b6f complex and
back to P700. This cyclic electron flow is coupled to proton pumping into the thylakoid lumen. When
protons flow their electrochemical gradient through ATP synthase complexes, ATP synthesis occurs.
The formation of ATP due to light induced cyclic electron flow is called cyclic phosphorylation. There
is no transfer of electrons from PSI to NADP for acceptor as NADPH, is no longer available and there
is no release of O2.
 In plants, the cyclic flow of electrons is utilized only when the concentration of NADPH is sufficient,
still needs ATP to power other activities in the chloroplast. Cyclic phosphorylation is somewhat more
productive as compared to non-cyclic photophosphorylation with regard to ATP synthesis.

24. Cyclic Electron Flow

25. Difference between CyclicandNon-cyclic?
Cyclic Non- cyclic
It involves PSI only It involves both PSI &
PSII
It synthesize only ATP It constitute with
synthesis of ATP &
NADPH.
It is not connected
with the photolysis of
water. Therefore, O2 is
not evolved.
It is connected with the
photolysis of water.
Therefore, O2 is
liberated.

26. DifferencebetweenPS – I & PS – II?
PS – I PS – II
Consist of pigment molecule
absorbing both longer &
shorter wavelength of light.
Consist of pigment molecule
absorb both only shorter
wavelength of light.
The reaction center is P700 The reaction center is P680
Lies on the outer surface of
Thylakoid.
Lies on the inner surface of
Thylakoid.
In this system molecular O2 is
not released.
In this system molecular O2 is
released by photolysis of
water.
Participation in both cyclic
flow of electron.
It involves only non-cyclic
flow of electron.

27. THANK YOU !