Lecure 30 Flashcards
All organisms can be classified in the basis of 2 aspects of their nutrition. What are they
Carbon source and energy source
Organisms contain carbon in one of 2 ways
Autotroph (self. Nourishing) carry out carbon fixation using CO2 as a carbon source; aka primary producers
Heterotrophs must consume carbon
Autotroph
Autotroph (self. Nourishing) carry out carbon fixation using CO2 as a carbon source; aka primary producers
Heterotroph
Must consume carbon
Organisms contain energy in one of 2 ways
Phototrophs: photosynthetic organisms that use light as their energy source
Chemotrophs: must obtain their energy chemically
Phototrophs
Photosynthetic organisms that use light as their energy source
Chemotrophs
Must obtain energy chemically
Photo autotrophs consist of
Consists of plant algae and Cyanobacteria
Photosynthesis def
Process by which all photoautotrophs use light energy to make surfaces and other organic food molecules from CO2 and water. It creates the biomass on earth and atmospheric oxygen (O2)
In eukaryotes where does photosynthesis take place
Chloroplasts
Chloroplast
Organelle found in plants and photosynthetic protists
Absorbs sunlight and uses it to power the synthesis of organic food molecules (sugars)
Chloroplast structure
Outer and inner membranes
Strong
Thylakoid
Thylakoid membrane
Thylakoid lumen
Thylakoids
Part of chloroplast
Light absorption by chlorophylls and carotenoids
Electron transport
ATP synthesis by ATP synthase
Stroma
Part of chloroplast
Space around thylakoids
Calvin cycle is here
Photosynthesis formula
6CO2 + 12H2O + light energy ->
C6H12O6 + 6O2 + 6H2O
2 unique rxns in chloroplasts
Light reaction
Carbon fixation
Light reaction photosynthesis def
Light driven production of ATP (photo-phosphorylation) and NADPH
Carbon fixation
Conversion of CO2 to carbohydrates in photosynthesis
Oxidation rxn in photosynthesis
Oxidation of water
2H2O + light energy -> O2 + 4H+ + 4e-
Reduction rxn in photosynthesis
Reduction of CO2
CO2 + 4H+ + 4e- -> (CH2O) + H2O
Photons
Light carries packets of electromagnetic energy called photons
Amount of energy a photon carries is proportional to
Wavelength
Plants absorb what type of light energy
Mainly blue and mainly red regions of visible light
Major class of molecules that are efficient at absorbing light are
Pigments
What happens when pigment absorbs a photon of light energy
Pigments chill at excited (high energy) or ground state (lower energy)
When they absorbs the photon one of its electrons become excited
When an excited pigment returns to ground state what happens
It’s energy is dissipated as heat or as an emission of fluorescence light
Energy transferred to a neighbouring pigment and further excites an electron in the second pigment molecule
Passes its excited electron to a neighbouring electron receptor molecule
Thylakoid membranes contain several kinds of pigments
What’s the main one
And the others
Chlorophyll is the main one (containing a porphyrin ring with a Mg++ in the center and a long hydrophobic side chain)
Chlorophyll a
Chlorophyll b
Carotenoids
Chlorophyll a
Initiates the light dependent reaction (as primary electron donor in the electron transport chain and also transferring resonance energy in the antenna complex)
Chlorophyll b
An accessory pigment that also participates in light absorption
Carotenoids
Another accessory pigment that absorbs different wavelengths of light
Orange and red
Photo system
Composed of a large antenna complex of pigments that surrounds a central reaction center
Chlorophyll molecules in the thylakoid membrane are associated with chlorophyll-binding proteins and organized into units called antenna complexes (light harvesting complex)
Each antenna complex absorbs light energy and transfers it to the reaction center
Reaction center is a complex of chlorophyll molecules (chlorophyll a) and proteins, including the primary electron acceptor, which participate directly in photosynthesis
Function of a photosystem is to trap photons of light and use the energy to oxidize a reaction center chlorophyll and enable the electron to be transferred to the primary electron acceptor
Antenna complex/ light harvesting complex
Chlorophyll molecules in the thylakoid membrane are associated with chlorophyll-binding proteins and organized into units called antenna complexes (light harvesting complex
Each antenna complex absorbs light energy and transfers it to the reaction center
Reaction center
Reaction center is a complex of chlorophyll molecules (chlorophyll a) and proteins, including the primary electron acceptor, which participate directly in photosynthesis
Function of a photosystem
Absorption of light energy
Transfer energy to the neighbouring chlorophyll molecules
Extract and transfer electrons to primary electron acceptors in the electron transport chain
In PS II, H2O is split, releasing O2
Function of a photosystem is to trap photons of light and use the energy to oxidize a reaction center chlorophyll and enable the electron to be transferred to the primary electron acceptor
Photosystem I
Specialized chlorophyll a in the reaction center is called P700 (P= pigment)
Absorption maximum at 700nm
Photosystem II
Specialized chlorophyll a in the reaction center is called P680
Absorption maximum at 680nm
Synthesis of ATP and NADPH by concerted action of ____ via noncyclic electron transport
Synthesis photo systems 1 and 2
Electron transport chains in photosynthesis
Similar to cellular respiration
Consisting of a series of electron carrier molecules in the thylakoid membrane
Through a non cyclic pathway carries the flor of electrons extracted from H2O to NADP+
2 photons of light, one absorbed by photosystem 2 and another absorbed by photosystem 1 are required to overcome the energy difference between H2O and NADP+
When PS II (P680) is activated by absorbing photons, it (chlorophyll a) gives energized electrons to a primary electron acceptor. These are passed along the ETC and eventually donated to PS I
PS II that has given yo an electron is + charged and functions as a strong oxidizing agent and is capable of pulling electrons away from H2O
A photolysis rxn catalyzed by manganese containing enzyme with the release of O2 as a by-product
Electrons transferred to PS I are reenergized by the absorption of additional light energy
These reenergized electrons are passed along the electron transport chain again
In photosynthesis the final electron acceptor is NADP+ (not O2) forming NADPH
1/3 of the energy of the photons absorbed by the 2 photosystems is used to transfer electrons from water to NADP+
Energy released during electron flow also drives the transport of hydrogen ions across the thylakoid membrane
1/8 of light energy absorbed by the 2 photosystems is used to pump protons into the lumen of the thylakoids
The high energy molecules NADPH is released into the stroma and will be used in the rxn for carbon fixation
Synthesis of ATP is driven by Chemiosmosis (photophosphorylation)
PS I rxn
Ferredoxin (Fd) -> NADP reductase
PS II rxn
Plastoquinone (Q) -> Cytochrome b complex (H+ pump) -> plastocyanin (PC)
