Chloroplast and Photosynthesis
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Transcript of Chloroplast and Photosynthesis
PHOTOSYNTHESISPHOTOSYNTHESISenergy for energy for lifelife
The site..The site..
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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