///// Light Dependent Reactions //////
- the reaction in photosynthesis which traps energy from the sun with the help of proteins and pigment molecules to create ATP and NADPH
- in plants there are two photosystems which absorb different wavelengths of light: photosystem I and photosystem II (found in the thylakoid membrane of the chloroplast)
- when a P680 molecule (located in the reaction centre of photosystem II) receives light wavelength of 680, it is excited and has the ability to pull electrons from water (resulting in H+ ions and oxygen molecules)
- energized electrons are transferred via electron transport system, releasing a small amount of energy in the process. b6-f complex uses this energy to pump hydrogen ions from the stroma into the thylakoid space
- PHOTOSYSTEM I: light that is absorbed by photosystem I is transferred to reaction centre p700 molecule (which needs light wavelength of 700 to get excited)
- NADP reductase uses electrons that were received by electron acceptor from photosystem I to reduce NADP+ to form NADPH
- photophosphorylation: use of photons of light to drive the phosphorylation of ADP to produce ATP via chemiosmosis (non-cyclic and cyclic)
- non cyclic photophosphorylation: bs6
Light Independent Reactions:
- the reaction in photosynthesis that assimilates co2 to produce an organic molecule that can be used to produce biologically important molecules such as carbohydrates AND DOES NOT REQUIRE LIGHT (fueled by light dependent reactions)
- CO2 assilmilation: carried out by the Calvin Cycle
- Calvin Cycle converts CO2 to glyceraldehyde-3-phosphate (G3P)
Step 1:
- Carbon dioxide fixation
- bond between carbon atom in CO2 to a pre-existing molecule in stroma called RUBP (ribulose-1,5-biphosphate)
- compound with 6 carbons is unstable and breaks down to the stable product PGA (3-phosphoglycerate)
Step 2:
- Reduction
- the 3-carbon compounds are in low energy state- they are activated by ATP then reduced by NADPH to convert them into a higher enegry state
- this results in two molecules of glyceraldehyde-3-phosphate (G3P)
- some G3P molecules leave cycle in their higher energy state and have the potential to form glucose and other carbohydrates
Step 3:
- Regenerating RuBP
- remaining G3P moelducles from step 2 move onto this phase where RuBP is replenished to keep the cycle going
- most of these molecules are used to make more RuBP
- Energy from ATP breaks and reforms bonds to make RuBP (5 carbons) from G3P
- calvin cycle must be completed 6 times in order to synthesize one molecule of glucose
