PHOTOSYNTHESISPHOTOSYNTHESISenergy for energy for lifelife

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LEAF MORPHOLOGYLEAF MORPHOLOGY External leaf characteristics (such as shape, External leaf characteristics (such as shape,

margin, hairs, etc.) are important for identifying margin, hairs, etc.) are important for identifying plant speciesplant species

These structures are a part of what makes leaves These structures are a part of what makes leaves determinant; they grow and achieve a specific determinant; they grow and achieve a specific pattern and shape, then stop. pattern and shape, then stop.

Other plant parts like stems or roots are non-Other plant parts like stems or roots are non-determinant, and will usually continue to grow as determinant, and will usually continue to grow as long as they have the resources to do so. long as they have the resources to do so.

Classification of leaves can occur through many Classification of leaves can occur through many different designative schema, and the type of leaf different designative schema, and the type of leaf is usually characteristic of a species, although is usually characteristic of a species, although some species produce more than one type of leaf.some species produce more than one type of leaf.

EPIDERMIS Generally a single layer of cells The "skin" of the plant Primarily parenchyma cells Main role is protection of the plant Often covered with trichomes that may limit the

transpiration Also typically covered with stomata for gas exchange Usually transparent and lack chloroplasts Coated on the outer side with a waxy cuticle that

prevents water loss

Function of epidermis :

protection against water loss,

regulation of gas exchange,

secretion of metabolic compounds,

absorption of water

Dicot Leaf Cross Section

Monocot Leaf Cross Section

THE MESOPHYLLTHE MESOPHYLL

THE CHLOROPLASTTHE CHLOROPLAST

THE STRUCTURE..THE STRUCTURE..

The word chloroplast is derived from the The word chloroplast is derived from the Greek words Greek words chloros chloros which means green which means green and and plastplast which means form or entity. which means form or entity. Chloroplasts are members of a class of Chloroplasts are members of a class of organelles known as plastids.organelles known as plastids.

INNER MEMBRANEINNER MEMBRANE

Inner membrane surrounds the stroma of Inner membrane surrounds the stroma of the plastidthe plastid

Extension of the inner membrane form Extension of the inner membrane form the thylakoid membrane.the thylakoid membrane.

the photosystem for photosynthesis is the photosystem for photosynthesis is occur at thylakoid membraneoccur at thylakoid membrane

GRANUMGRANUM

Refer to :Refer to : A A thylakoid stack (granum, pl. grana) stack (granum, pl. grana)

inside chloroplasts. inside chloroplasts. A granum (plural grana) is a stack of A granum (plural grana) is a stack of

thylakoid discs. Chloroplasts can have thylakoid discs. Chloroplasts can have from 10 to 100 grana. from 10 to 100 grana.

Grana are connected by stroma Grana are connected by stroma thylakoids, also called intergrana thylakoids, also called intergrana thylakoids or lamellae. thylakoids or lamellae.

Grana thylakoids and stroma thylakoids Grana thylakoids and stroma thylakoids can be distinguished by their different can be distinguished by their different protein composition. protein composition.

STROMASTROMAThe inner matrix of the chloroplast The inner matrix of the chloroplast A colourless matrix in which the A colourless matrix in which the lamellae are embeddedlamellae are embeddedA matrix containing dissolved A matrix containing dissolved enzymes enzymes A fluid surrounds the double A fluid surrounds the double membrane of chloroplastmembrane of chloroplast

FUNCTIONS OF STROMAFUNCTIONS OF STROMA

It contain enzyme-rich solution which are It contain enzyme-rich solution which are the place where carbon dioxide is first the place where carbon dioxide is first attached to an organic compound and attached to an organic compound and reduced to carbohydrates (calvin cycle) reduced to carbohydrates (calvin cycle)

The reactions occur and starches The reactions occur and starches (sugars) are created in stroma(sugars) are created in stroma

THYLAKOIDTHYLAKOIDAny of the flattened saclike structures Any of the flattened saclike structures that are stacked on top of another to that are stacked on top of another to form the grana.form the grana.Chlorophyll and other photosynthetic Chlorophyll and other photosynthetic pigment are situated in the thylakoid pigment are situated in the thylakoid membranes.membranes.

LUMENLUMENComes from Latin word lumen opening /lightComes from Latin word lumen opening /lightThe cavity of a tubular organ in thylakoidThe cavity of a tubular organ in thylakoidFunction as Function as

a)a)Play a vital role for photophosphorylation Play a vital role for photophosphorylation during photosynthesis.during photosynthesis.

b)b)Site of water oxidation by the oxygen Site of water oxidation by the oxygen c)c)The present of electron transport protein The present of electron transport protein

plastocyanin in lumen.plastocyanin in lumen.

PHOTOSYNTHESIS

CONCEPTCONCEPT

Chloroplasts absorb light and use it in Chloroplasts absorb light and use it in conjunction with water and carbon dioxide to conjunction with water and carbon dioxide to produce sugars, the raw material for energy produce sugars, the raw material for energy and biomass production in all green plants and and biomass production in all green plants and the animals that depend on them, directly or the animals that depend on them, directly or indirectly, for food.indirectly, for food.

LIGHT REACTIONLIGHT REACTION

PHOTORECEPTORSPHOTORECEPTORS

ChlorophyllChlorophyll

Consist of 2 parts :Consist of 2 parts : (i) porphyrin; head (i) porphyrin; head (ii) long hydrocarbon @ phytol; tail(ii) long hydrocarbon @ phytol; tail

Made up of 4-nitrogen containing pyrrole ring Made up of 4-nitrogen containing pyrrole ring MgMg2+ 2+ in the center of the ring in the center of the ring Four species of chlorophyll : Four species of chlorophyll : aa, , bb, , cc and and dd

Structure of Chlorophyll a Structure of Chlorophyll a

Mg

N

N

N

N

CH3

CHOCH2

CH

CHO

O

CH2

CH2

C=O

CH

CH2

Chlorophyll a

Chlorophyll c

Chlorophyll d

Chlorophyll b

pheophytin

I II

IIIIV

Absorption spectra of chlorophyll a and Absorption spectra of chlorophyll a and chlorophyll bchlorophyll b

400 500 600 700

Chlorophyll b

Chlorophyll a

Ab

sorp

tio

n

Wavelength (nm)

LIGHT ABSORPTIONLIGHT ABSORPTION

Chlorophyll does not absorb strongly Chlorophyll does not absorb strongly green of the visible light spectrum (490-green of the visible light spectrum (490-550nm) 550nm)

Maximum absorption: blue light (425-Maximum absorption: blue light (425-490nm) and red (640-700nm)490nm) and red (640-700nm)

PHOTOSYSTEMPHOTOSYSTEM Photosystem (PS) are major components of the photosynthetic Photosystem (PS) are major components of the photosynthetic

electron transport chainelectron transport chain

PS; presence of 2 large multi molecular complexes : PS; presence of 2 large multi molecular complexes : Photosystem Photosystem I (PSI)I (PSI) and and photosystem II (PSII)photosystem II (PSII)

These 2 photosystems operate in series linked by a multiprotein These 2 photosystems operate in series linked by a multiprotein aggregate; called aggregate; called cytochrome complexcytochrome complex

PSI is designated as PSI is designated as P700P700 (pigment with maximum absorbance at (pigment with maximum absorbance at 700nm)700nm)

PSII designated as PSII designated as P680P680 (pigment with maximum absorbance at (pigment with maximum absorbance at 680nm)680nm)

ELECTRON TRANSPORT CHAINELECTRON TRANSPORT CHAIN

H2O

½O2 + 2H+

2ePSII PSICyt

NADP+ + 2H+

NADPH + H+

⇨⇨ sequential arrangement of 3 molecules membrance sequential arrangement of 3 molecules membrance complexes extracts to low-energy electron (from water) complexes extracts to low-energy electron (from water) and used light energy, produces strong reductant; and used light energy, produces strong reductant; NADPH + and H+NADPH + and H+

Arrangement of PS I, PSII and Arrangement of PS I, PSII and complex (Cyt complex (Cyt bb66/f)/f) in thylakoid membranein thylakoid membrane

4 complexes; CF4 complexes; CF00 – CF – CF1 1 coupling factor @ ATP coupling factor @ ATP synthasesynthase

Arrangement - direct movement of protons Arrangement - direct movement of protons between the stroma and thylakoidbetween the stroma and thylakoid

This arrangement give rise to proton gradient This arrangement give rise to proton gradient for ATP synthesisfor ATP synthesis

PHOTOLYSIS OF WATERPHOTOLYSIS OF WATER

Water splitting: 2HWater splitting: 2H22O OO O22 + 4H + 4H++ + 4e + 4e Occur in PSIIOccur in PSII Donate electron and protonDonate electron and proton Product - oxygenProduct - oxygen

PHOTOPHOSPHORYLATIONPHOTOPHOSPHORYLATION

PhotophosphorylationPhotophosphorylation ⇨⇨ light-driven production of ATP light-driven production of ATP by chloroplastby chloroplast

ATP and NADPH are required for reduction ofATP and NADPH are required for reduction of CO CO22

Formation of ATP through:Formation of ATP through: i. noncyclic @ linear electron transport known as i. noncyclic @ linear electron transport known as

noncyclic photophorylation; and noncyclic photophorylation; and ii. cyclic electron transport known as cyclic ii. cyclic electron transport known as cyclic

photophosphorylationphotophosphorylation

NONCYCLIC NONCYCLIC PHOTOPHOSPHORYLATIONPHOTOPHOSPHORYLATION

Electron continously supplied from water and Electron continously supplied from water and transfer to NADPtransfer to NADP++ to from NADPH to from NADPH

Establish proton gradient, which in turn drives Establish proton gradient, which in turn drives ATP synthesisATP synthesis

Produce ATP and NADPHProduce ATP and NADPH

P680

P700*

P700

P680*

Feo

PQCytb6/f

PC

fd

NADP+

H2O ½ O2 + 2H+

Redox potential

+1.0

0

-0.6

2 hv≤680 nm

2 hv>680 nm

CYCLIC PHOTOPHOSPHORYLATIONCYCLIC PHOTOPHOSPHORYLATION

Transport electron independently of PSII @ PSI Transport electron independently of PSII @ PSI

operating independently of PSIIoperating independently of PSII

Return electron from Return electron from P700*P700* to to P700 P700 throughthrough Ferridoxin Ferridoxin

(Fd), ferrodoxin-PQ oxidoreductase (Fdx-PQ), (Fd), ferrodoxin-PQ oxidoreductase (Fdx-PQ),

cytochrome cytochrome bb66ff complex and Plastoquinone (PC) complex and Plastoquinone (PC)

Oxidation of PQ by cytochrome Oxidation of PQ by cytochrome bb66ff complex generates complex generates

proton gradient that can be used for ATP synthesis but proton gradient that can be used for ATP synthesis but

no NADPH producedno NADPH produced

P700*

P700

Fd

PQ

Fdx-PQ

PC

FeS Cyt f

PSI

hv>680 nm

Cyclic electron transport

ATP SYNTHESISATP SYNTHESIS ChemioosmosisChemioosmosis

In chloroplast, protons are pumped across thylakoid In chloroplast, protons are pumped across thylakoid membrane, from stroma into the lumen membrane, from stroma into the lumen

Protons carry positive charge Protons carry positive charge ⇨⇨ difference in proton difference in proton concentration (∆ pH) across the membrane quite largeconcentration (∆ pH) across the membrane quite large

Proton motive forceProton motive force (pmf) = membrane potential (pmf) = membrane potential difference + proton gradientdifference + proton gradient

Pump proton into lumen against a proton motive force & Pump proton into lumen against a proton motive force & large amount of energy is requiredlarge amount of energy is required

Energy required is provided by free energy from Energy required is provided by free energy from intersystem electron transport in photosynthesisintersystem electron transport in photosynthesis

Direction of proton motive force favors the return of Direction of proton motive force favors the return of proton to the stromaproton to the stroma

Return of proton restricted to proton-lined channel, i.e. Return of proton restricted to proton-lined channel, i.e. ATP synthaseATP synthase

Model of Chloroplast ATP synthaseModel of Chloroplast ATP synthase

H+

Active site for ATP synthesis

Channel to allow proton return back to stroma

stroma

Thylakoid membrane

Lumen

ATP Synthase complexs

H+

pH8

pH5

CF1

CF0

SUMMARYSUMMARY

Photochemical reactionsPhotochemical reactions

Occur in Occur in thylakoidsthylakoids and and granagrana, produce , produce OO22, ,

ATPATP, and , and reduced NADPreduced NADP+ + (or NADPH).(or NADPH).

CALVIN CYCLECALVIN CYCLE

Pathway which all organisms (photosynthetic Pathway which all organisms (photosynthetic eukaryotic) incorporate COeukaryotic) incorporate CO22 into carbohydrate; into carbohydrate;

known as known as carbon fixation @ Photosynthetic carbon fixation @ Photosynthetic Carbon Reduction (PCR) cycle @ Calvin cycleCarbon Reduction (PCR) cycle @ Calvin cycle

Consume Consume ATPATP and and NADPHNADPH produced by produced by photosynthetic electron transportphotosynthetic electron transport

STAGESSTAGES PCR cycle divided into 3 primary stage :PCR cycle divided into 3 primary stage :

(i) (i) CarboxylationCarboxylation ⇨ ⇨ fixes COfixes CO22 in the presence in the presence of 5-C acceptor molecule; ribulose of 5-C acceptor molecule; ribulose bisphosphate (RuBP); and converts into 2 bisphosphate (RuBP); and converts into 2 molecules of 3-C acidmolecules of 3-C acid

(ii) (ii) ReductionReduction ⇨ ⇨ consume the ATP and NADPH consume the ATP and NADPH produced by photosynthetic electron transport produced by photosynthetic electron transport to convert the 3-C acid to triose phosphateto convert the 3-C acid to triose phosphate

(iii) (iii) RegenerationRegeneration ⇨⇨ consume additional ATP to consume additional ATP to convert some of the triose phosphate back into convert some of the triose phosphate back into RuBP to ensure the capacity for the continuous RuBP to ensure the capacity for the continuous fixation of COfixation of CO22

CO2

PGA

glucose

6 1,3-biphosphoglycerate

G3P

G3P

ATP

G3P

RuBP

ADP

NADP+ 6Pi

NADPH

3 ADP

ATPCalvin Cycle

Rubisco