Lecture 4-Chloroplast Flashcards
How often do plants replenish atmospheric content of oxygen
every 2000-3000 years
Three steps of photosynth
photochemistry, electron transfer and production of NADPH and ATP
incorporation of CO2 into carb and production of O2
Pigments
transfer radiant energy to chemical bonds, many double bonds that interact with photons
Enzymes
transfer chemical energy
Light reactions driven by photons entering chloroplast
2h2o>o2+4h+
3ADP+3Pi>3ATP
2NADP+ +2H+>2NADPH
Chloroplast double membrane
no PS, allows passage of small compounds, water, some proteins
Stroma
liquid, dark reactions
site of ATP and NADPH accumulation
Thylakoid membrane
light reactions
Thylakoid space
light reactions
Thylakoids
site of photosystems 1 and 2
3 Light absorbing compounds
chlorophylls (a and B)
Cartenoids
Phycobilins (red algae and cyanobacteria which have a and c but no b)
Interaction between photons and double bonds of pigments depends on
molecular structure
length of carbon chain
number of d.b in chain
structures at end of chain
Primary electron acceptor
2 chla coupled to protein, chla without magneisum
Trap chlorophyll
chla and protein
P680chl a/protein complex
680 nm (red light)
P700 chl a/protein complex
700nm (far red light, people cannot see)
Resting P680
powerful oxidant, readily accepts electron.
readily splits water, releasing protons and oxygen
excited P680
excited by photons from chl a reactive centre, electrons torn from water are boosted to a higher state and passed along to another compound (pheophytin). falls back to unexcited state, cycle begins again
Non-cyclic photophosphorylation
excited P680 passes e to pheophytin in Photosystem II. Pheophytin passes e to quinone.
Quinone gives to cytochrome b6/f
Passed to PSI, chla passes energy to P700.
boosted to excited state by photons. e donated to PSI which forms NADPH.
ATP and NADPH in equal amounts. O2 is byproduct
PSII
electron transport chain that releases energy in form of a proton. Proton enters thylakoid space, joining protons split of H2O, resulting in proton gradient that drives ATP synthase
PSI
harvests light, different absorption spectrum.
NADPH
electron carrier for biosynthetic reactions
Purpose of having 2 PS
one creates pool of protons to drive ATP formation
one creates pool of energy rich NADPH
Cyclic photophosphorylation
ATP production uncoupled from NADPH (more ATP can be produced than NADPH)
e recycling
PSII passes e to PSI, gets excited and passes e to ferredoxin which passes e back to cyb6/f, releasing proton, forming only ATP
Photophosphorylation
creation of ATP using proton gradient that is light dependent
