Photosynthesis Flashcards
Pigment that makes leaves green, absorbs light principally in the violet and the blue wavelengths and also in the red, and reflects green light
Chlorophyll
Process involving conversion of the energy present in sunlight to energy present in organic molecules
Photosynthesis
Primary photosynthetic pigment that comprises about 75% of the total chlorophyll in most plants.
It is also found in all photosynthetic eukaryotes and blue-green algae.
Chlorophyll a
Difference between chlorophyll a and chlorophyll b structure.
Chlorophyll b has -CHO group in place of the -CH3 group of chlorophyll a
Accessory pigment that transfers energy to chlorophyll a during photosynthesis; accounts for 25% of the total chlorophyll
Chlorophyll b
Accessory pigment that replaces chl b in some algae, specifically brown algae
Chlorophyll c
Accessory pigments that are not chlorophyll:
Carotenoids (Carotenes and xanthophylls)
Phycobilins
2 major process of photosynthesis
Light reactions and carbon fixation reactions
Light reactions happen where?
Thylakoid membrane
Carbon fixation happens where?
Stroma
What happens during light reactions?
- Energy from sunlight is converted to electron flow
- oxygen is released as a byproduct
- products are ATP and NADPH
- comprise of 2 photosystems
Light harvesting components of the photosystems. It has pigment molecules that gather light energy and “funnel” it to the reaction center
Antennae complex
Photosystems consist of:
Antennae complexes
Reaction center chlorophylls
electron transport proteins
Special chlorophyll a molecules of the rxn center in Photosystem I
P700
Special chlorophyll a molecules of the rxn center in Photosystem II
P680
What happens in photosystem II?
- Light energy (2 photons) enters PII and is trapped by pigment molecules and passed to P680 of rxn center.
- Energized electrons are transferred from P680 to an electron acceptor.
- As the electrons are removed from P680, they are replaced by low-energy e- from water molecules and oxygen is produced (photolysis)
- Pairs of electrons pass down downhill to photosystem I along ETC
Factors that contribute to protomotive force
Concentration gradient and charge separation
Potential energy that contributes to the production of ATP via the ATP synthase using the proton gradient
Protomotive force
Function is to split water (which contributes to the proton gradient) and it also steals 2 electrons, which then are donated to rxn center to replace the electrons lost;
Essential cofactor is manganese
Oxygen evolving complex
Which part of PII pumps protons across the membrane, generating the proton gradient?
Cytochrome b/f
What happens in photosystem I?
- Light energy is absorbed and passed to P700 of the reaction center.
- The energized electrons are accepted by coenzyme NADP+, and electrons removed from P700 are replaced by electrons from photosystem II
- Passing of electrons down carriers reduces NADP+ to NADPH
Unidirectional flow of electrons from water to NADP+
Noncyclic electron flow
What does linear electron transport produces?
1 ATP and 1 NADPH
What does cyclical electron transport/flow generates?
Only ATP
How does cyclical electron transport work?
Ferrodoxin transports 2 electrons back to cyt b/f
This results in translocation of 2 protons
This process require the products of the light reactions and where carbon fixation occurs
Calvin cycle
What happens during Calvin cycle?
- A molecule of CO2 combines with a 5-C sugar (RuBP) to form two molecules of 3-C compound (PGA).
- PGA is then reduced to 3-C molecule PGAL, with electrons provided by NADPH and energy by ATP.
- At each turn of the cycle, one carbon atom enters the cycle, and RuBP is regenerated.
- Fixed carbon is also generated to convert to either sucrose or starch
Ratio of the use of ATP and NADPH during Calvin cycle
3:2
Process by which the oxygenase activity of rubisco combined with the salvage pathway consumes O2 and releases CO2
Photorespiration
Difference between C4 and C3 plants
C3 only uses Calvin cycle , C4 uses C4 pathway and Calvin cycle
What happens during C4 pathway?
- Oxaloacetate is formed when CO2 is fixed to PEP in a reaction catalyzes by PEP carboxylase found in the mesophyll.
- Oxaloacetate is then reduced to malate or aspartate
- The malate/aspartate is moved to the bundle-sheath cells where it is decarboxylated to yield CO2 and pyruvate.
- CO2 is then used for Calvin cycle
Difference between CAM and C4 plants.
Cam plants have time separation
C4 has spatial separation of the two pathways (c4 and Calvin cycle)
What happens during CAM photosynthesis?
- CO2 is fixed in the dark through activity of PEP carboxylase in the cytosol
- Oxaloacetate is produced, then reduced to malate.
- Malate is stored as malic acid in the vacuole.
- During the day, malic acid is recovered from the vacuole, decarboxylated and CO2 is transferred to RuBP of the Calvin cycle w/in the same cell
