Chapter 14
Energy conversion From Foods: Mitochondria
Energy conversion & Free energy Works in hydroelectricity
Heat
Potential E
Kinetic E
Heat
Electrical E
FREE ENERGY : Energy available for this work (conversion)
Designs for ATP synthesis Chemiosmosis Chemiosmosis is the name given to the generation of ATP from a proton gradient. It occurs in all living things:
Energy
A Design for ATP synthesis:
Oxidative phosphorylation
Pyruvate CO2 + NADH NADH + O2 ATP + H2O
Another Design for ATP synthesis:
Light-induced phosphorylation Cyclic phosphorylation PS-I only
Non-cyclic phosphorylation PS-I and II
Cyclic Photophosphorylation • Process for ATP generation associated with some Photosynthetic Bacteria • Reaction Center => 700 nm
Noncyclic Photophosphorylation
Photosystem II regains electrons by splitting water, leaving O2 gas as a by-product Primary electron acceptor Primary electron acceptor
Photons
Energy for synthesis of PHOTOSYSTEM I PHOTOSYSTEM II
by chemiosmosis
Chapter 14 Energy conversion From Light:
Chloroplast
Green plants in Ecosystem
THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON EARTH
Autotrophs (self + nutrition in Greek) : an organism that produces complex organic compounds from simple inorganic molecules using energy from light (by photoynthesis) or inorganic chemical reactions.
The proximate cause…
Why are green? green? Why plants plants are
Why plants are green? Gamma rays
X-rays
UV
Infrared & Microwaves
Visible light
Wavelength (nm)
Radio waves
THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED
The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments
Light
Reflected light
Transmitted light
Chloroplast
Absorbed light
(i.e., chlorophylls, carotenoids).
• The location and structure of chloroplasts Chloroplast LEAF CROSS SECTION
MESOPHYLL CELL
LEAF Mesophyll
CHLOROPLAST
Intermembrane space Outer membrane
Granum Grana
Stroma
Inner membrane Stroma
Thylakoid
Thylakoid compartment
The location and structure of chloroplasts A chloroplast contains:
-stroma, a fluid -grana, stacks of thylakoids
The thylakoids contain chlorophyll -Chlorophyll is the green pigment that captures light for photosynthesis
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
outer membrane intermembrane space inner membrane (1+2+3: envelope) stroma (aqueous fluid) thylakoid lumen (inside of thylakoid) thylakoid membrane granum (stack of thylakoids) thylakoid (lamella) starch ribosome plastidial DNA plastoglobule (drop of lipids)
Absorbance of pigments in chloroplasts
– Chlorophyll-a – Chlorophyll-b Carotenoids
Chlorophyll a & b •Chl a has a methyl group •Chl b has a carbonyl group Porphyrin ring delocalized e-
Phytol tail
Chlorophyll-a
(type-a in green plants and algae)
Beta-carotene (Mostly in algae)
Chlorophyll-b
(type-b in green plants and algae)
Chloroplast
Dark reactions
for Photosynthesis
PHOTOSYNTHESIS Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
Carbon dioxide
Water
Glucose PHOTOSYNTHESIS
Oxygen gas
Photosynthesis
Light and Dark reactions Light reactions: 12H2O + 12NADP + 18ADP → 6O2 + 12NADPH + 18ATP
Dark reactions: 6CO2 + 12NADPH + 18ATP → C6H12O6 + 12NADP + 18ADP + 6H2O Two distinct stages, the light reactions, which convert light energy to ATP and NADPH; and the dark reactions, which convert CO2 to carbohydrate using ATP and NADPH. Both occur in the chloroplasts.
Photosynthesis
Light and Dark reactions Light
NADP
Light reactions
Calvin cycle
Photosynthesis
Two types of photosystems in the light reactions By theory, it appears to takes just four electrons (and four protons) to reduce CO2 to carbohydrate. However, we find we need eight photons per CO2, implying that two photochemical reactions are needed per electron, and that there are two kinds of photosystem operating in series, each physically separate in its own kind of particle. ATP mill
Water-splitting Photosystem II
NADPH-producing Photosystem I
PSII: Plants produce O2 gas by splitting H2O
The O2 liberated by photosynthesis is made from the oxygen in water (H+ and e-)
Photosystem II
PSII Chemiosmosis for ATP production Thylakoid compartment (high H+)
Light
Light
Thylakoid membrane
Antenna molecules Stroma (low H+)
Reaction center
ELECTRON TRANSPORT CHAIN
PHOTOSYSTEM II
PHOTOSYSTEM I
ATP SYNTHASE
PSII
(PSII+ LHC)
Resonance transfer of electrons to PSII
PSII
(water oxidase system)
Antenna a complex of
the pigment molecules are arranged in
blocks of about 50
The reaction centre, where the photochemical reaction occurs. The excited chlorophyll-a ejects an electron, becoming an extremely strong oxidising agent, capable of pulling electrons out of water. The antenna plus the reaction centre taken together are termed a photosystem.
P680, Chlorophyll-b mainly absorb 60 nm light
LHC-II
(Light-harvesting complexes) 1) Resonance transfer of photons
From LHC to PSII 2) Preventing ‘Back-up’ of electrons This is important because if photosystem I receives too little energy compared to PSII, electrons will 'back up' the transport chain, and prevent excited electrons from escaping photosystem II.
2) Preventing ‘Photoinhibition’ Excited chlorophyll molecules in photosystem II will not be quenched by electrons from water, and will cause oxidative damage to the reaction centre. This causes the destruction of photosystem II,
LHC-II phosphorylated Association with PSII
Green, Chlorophyll-a/b; Yellow, Cartenoids
Too much light LHC-II de-phosphorylated Dissociation with PSII
An Energy spacer?
Light pumping to P680 When a chlorophyll molecule within the LHC contacts a photon of light, resonance energy is produced. This resonance energy is transferred through several more chlorophyll molecules until it reaches the P680 chlorophyll molecules at the heart of the Photosystem II reaction center. The resonance energy causes the loss of an electron from the P680 molecules. This electron is then transferred to a pheophytin molecule, then to Qa and finally to Qb. P680 is then reduced by the splitting of a water molecule which replaces the electron lost in this process.
Why photons in LHC are channeled to PSII?
An Energy spacer?
Resonance transfer of photons LHC
P680 or P700 LHC P680
E=hc⁄λ h, Planck's constant, 6.6 × 10−34 J s. c, speed of light, 3 × 108 m s−1.
Blue light is more energetic
The ultimate cause…
Why plants green? Plants must are be green? LHC
P680, 700
Transfer of electrons Primary electron acceptor Primary electron acceptor
Energy to make
NADP
3
2 Light
Light Primary electron acceptor
1
Reactioncenter chlorophyll
Water-splitting photosystem 2 H + 1/2
P680 become hungry for e- and take it from water
NADPH-producing photosystem
PSI
(ferredoxin reductase system)
Chemiosmosis for ATP production Thylakoid compartment (high H+)
Light
Light
Thylakoid membrane
Antenna molecules Stroma (low H+)
Reaction center
ELECTRON TRANSPORT CHAIN
PHOTOSYSTEM II
PHOTOSYSTEM I
ATP SYNTHASE
Chemiosmosis
in PSII + electron transport chains
• A Photosynthesis Road Map Chloroplast Light Stroma NADP
Stack of thylakoids
ADP +P Light reactions
Calvin cycle
Sugar used for Cellular respiration Cellulose Starch Other organic compounds
The Calvin Cycle 3 CO2 + 6 NADPH + 5 H2O + 9 ATP → C3H5O3-PO32- + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi
RUBISCO
From Photosynthesis
Photosynthesis uses light energy to make food molecules Chloroplast Light
Photosystem II Electron transport chains Photosystem I
CALVIN CYCLE
A summary of the chemical processes of photosynthesis
Stroma
Cellular respiration Cellulose Starch LIGHT REACTIONS
CALVIN CYCLE
Other organic compounds