Photosynthesis - Light Dependent

Question 1

Photosystems for photosynthesis

Answer 1

Photosystem Antenna complex (photo):

Antenna complex + Reaction center + chlorophyll-a pigments = Photosystem

1) chlorophyll molecules on Antenna complex: capture & transfer E of photon to Reaction Center by passing to each other
(Proteins orient pigment in optimal light absorption direction)

2) Reaction center (transmembrane protein-pigment complex): trap for light E
Energy excites electron in reaction Center, electron passed to electron acceptor (quinone)

3) lost electron replaced by electron donor (water in plants)

Question 2

Light dependent rxn

Answer 2

Thylakoid & Thylakoid membrane
Presence of light
Produce Energy required for light independent rxn

1) Primary Photoevent: pigments excited by photon
2) Charge Separation: E transferred to reaction center, electron to electron acceptor
3) Electron transport: excited electron to electron transport chain, create proton gradient, reduce final electron acceptor to NADPH
4) Chemiosmosis: protons pumped during electron transport chain flow back across membrane—-> ATP

Question 3

Order of light dependent rxn (photo)

Answer 3

Photosystem 2 (peak 680nm - P680 - higher E)
b6-f complex
Photosystem 1 (peak 700nm - P700 - lower E)
NADP reductase

Question 4

Steps of electron transport chain

Answer 4

1) excited electron sent to quinone molecule
2) Manganese + proteins oxidized water—> regain lost electron, produce O2
(4 photons, oxydation of 2 water (2 e-), 2 oxygen)

3) quinone carries electron to b6-f complex (e transport chain)
b6-f Complex: proton pump (E from electrons to pump protons into Thylakoid lumen)
Chemiosmosis (ATP from ATP synthase)

4) plastocyanin: electron to PS1
5) PS1: photon energy absorbed in antenna complex, transfer to reaction Center, excited electron donated to ferroredoxin
6) lost electron replaced by incoming electron from PS2
7) ferroredoxin donates electron to NADP+—> NADPH (NADP reductase — stromal side of Thylakoid membrane)

NADPH: high energy electron carrier (coenzyme)
Carries energy from light to Stroma (generate high energy organic molecules- sugars - Calvin cycle)

Recap: Oxygen (oxidation of water)
ATP
NADPH (both high E to make sugar)