Photosynthesis 2 Flashcards
Describe carbon fixation in Calvin cycle:
CO₂ is fixed into an organic molecule.
The enzyme ribulose-1,5-bisphosphate carboxylase (RuBisCO) catalyses the reaction between CO₂ and RuBP, a 5-carbon molecule.
Produces an unstable 6-carbon compound that splits into two molecules of 3-phosphoglycerate (3-PGA), a 3-carbon compound
Describe reduction in Calvin cycle:
Each 3-PGA molecule is phosphorylated by ATP (from the light-dependent reactions) to form 1,3-bisphosphoglycerate.
Then, each 1,3-bisphosphoglycerate is reduced by NADPH (also from the light-dependent reactions) to form glyceraldehyde-3-phosphate
Describe regeneration in Calvin cycle:
One of the G3P molecules exits the cycle to contribute to the formation of glucose and the rest are used to regenerate RuBP
What is the difference between chemiosmosis in chloroplasts and mitochondria?
In mitochondria, protons are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix
In chloroplasts, protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma
Describe photon absorption II + water absorption step of light dependent reaction:
Photon Absorption and Water Splitting (PSII) - Light photons are absorbed by chlorophyll molecules in PSII, exciting electrons to a higher energy level. To replace the lost electrons, water molecules are split (photolysis), producing oxygen (O₂), protons (H⁺), and electrons.
Describe the electron transport chain of light dependent reaction:
As electrons move down the ETC from the primary electron acceptor of PSII to PSI, they lose energy, which is used to pump protons from the stroma into the thylakoid lumen, creating a proton gradient
Describe photon absorption I step of Calvin cycle:
Electrons reach PSI, where they are re-energized by photons absorbed by P700 chlorophyll molecules.
The re-energized electrons are transferred to the primary electron acceptor of PSI.
Describe NADPH formation in Calvin cycle:
The electrons are passed from PSI to a protein called ferredoxin (Fd) and then to the enzyme NADP⁺ reductase.
NADP⁺ reductase catalyzes the transfer of electrons to NADP⁺, along with a proton (H⁺), forming NADPH
Describe ATP formation in Calvin cycle:
The proton gradient created by the ETC drives protons back across the thylakoid membrane through ATP synthase.
The flow of protons through ATP synthase provides the energy needed to phosphorylate ADP to ATP
What is cyclic electron flow?
Electrons cycle back from Fd to the PS I reaction center
Cyclic electron flow uses only photosystem I and produces ATP, but not NADPH
No oxygen is released
What is linear electron flow?
primary pathway, involves both photosystems and produces ATP and NADPH using light energy
