Lecture 12- Photosynthesis Flashcards
What is a photosystem?
The combination of an antenna complex and a reaction center.
What is the antenna complex what is its role?
The antenna complex is an arrangement of chlorophyll pigments that pass the light energy around to get it to the reaction center.
Proteins present here also orient the complex towards light.
What is the reaction center?
A transmembrane protein-pigment which excites an electron using the energy harvested by the antenna complex. It then passes on the electron to an electron acceptor (plastoquinone).
What happens to the electron lost by the reaction center?
It is replaced by an electron from an electron donor (water).
What are the four light dependent reactions? Where do they occur?
- Primary photoevent. The pigments in the antenna complex are excited by a photon.
- Charge separation. The energy is transferred to the reaction center, where an electron is excited electron and passed on to plastoquinone.
- Electron transport. The excited electron is passed on to the electron transport chain, where a proton gradient is created to finally make NADPH.
- Chemiosmosis. Protons pumped during electron transport are flow back across the thylakoid membrane to synthesize ATP.
These reactions occur in the thylakoid and its membrane.
What are the peak absorptions of each photosystem? Which absorbs the greater energy?
Photosystem II, the first one, has 680 nm and absorbs more energy than Photosystem I, which has a peak absorption at 700 nm.
What is the b6-f complex?
The electron transport chain which uses the energy from the electron to pump protons into the thylakoid lumen.
What is the role of photosystem 1?
It takes the energy-depleted electron and reexcites it, then giving it to ferroredoxin, which donates it to NADP+ to make NADPH.
How is ATP generated during photosynthesis?
By chemiosmosis, the protons flow back into the stroma and power the oxidative phosphorylation of ADP to ATP by ATP synthase.
How is oxygen generated during photosynthesis?
When the exited manganese electron from the reaction center is donated to the plastoquinone (electron acceptor), that electron must be replaced. It is replaced when water is oxidized, giving 1/2 O2, 2 H+, and two electrons.
What is the role of the light dependent reactions and what is the next step?
The role of the light dependent reactions is to harvest the energy from the Sun and convert it to NADPH and ATP.
The next step is to use that energy for carbon fixation (creating sugars from CO2).
