Lecture 13: Photosynthetic Electron Transport Flashcards
Photooxidation reactions
convert light energy into chem energy
How is photosynthesis similar to ETS?
both have linked redox rxnts that generate a proton motive force
What are we oxidizing and reduce to what effect?
oxidize H2o to make O2
reduce NADP+ to make NADPH
What is NADHP NOT?
an electron source to drive synth of ATP (but it is still an electron carrier, just not used to make ATP)
What are ATP and NADPH chem nrg used for?
to convert CO2 to glyceraldehyde-3P in carbon fixation
what are the chem energy formse made by converting sunlight to chem nrg?
ATP
NADPH
what pathway does carbon fixation use to convert CO2 to GAP?
Calvin cycle
pants make sucrose for food at night
How much of wat do we need to make one molec of glucose?
6 H2O
6 CO2
light energy
The delta G value is postive, what does that mean??
where does the energy come from???
we are doing the reaction in the reverse direction of glycolysis
the energy comes from light!
Which metabolic pathway runs in the opposite direction of glycolysis and converts glyceraldehyde-3P (GAP) into glucose?
gluconeogenesis
What does the photosynethetic electron transport system (PETS) accomplish for the cell?
convert light energy into redox nrg
generate ATP by chemiosmosis and reduce NADP+ to make NADPH
What does carbon fixtion (Calvin cycle) accomplish for the cell?
the enzymes use nrg from ATP and NADPH to reduce CO2 to make glyceraldehyde-3P (3 carbon carb)
thse carbs are used as chem nrg for mitochondrial respiration
How many ATP used in SIX turns of calvin cycle?
What does 6 turns produce?
18 ATP used
GLUCOSE produced
It takes 18 ATP to make a glucose molecule. Is it worth it?
YES! because per glucose molecule, you make 30-32 ATP in mitochondrial respiration
key enzymes? (for oxidation )
Photosystem II (photoox) cytochrome b6f (proton pump, like complex 3) Photosystem I (photoox)
enzyme for photophosphorylation (convert proton motive force into net ATP synth)
chloroplast ATP synthase
very much like mitochondrial ATP synthase
Key enzyme for CO2 fixation in step 1 of calvin cycle
Rubisco
activitiy maximal in light
regulated activity!
Examples in real life: DCMU
herbicide. blocks electron flow through photosystem II
reduce weeds in non crop areas
Examples in real life: paraquat
herbicide
prevents reduction of NADP+ by accepting e- from intermediate reductants in PS I
key points about photosynthesis
e- come from water
excited by light photons
PSII->Q mole—>cytochrome b6f (q cycle from 2e- to 1 e-)–>thylakoid space–>PC–>PSI ( 4 photons light needed for excitement)–>feridoxin–>FAD–>ATP synthase
how many protons?
8 through cytochrome b6f
4 per 2 water molecules oxidized
total of 12 end up in thylakoid space (and then they go through ATP synthase ad make 3ATP)
so what is like NADH in mitochondrial? What drives the movement of protons?
Light energy (redox nrg of NADH used in METS)
Chloroplasts
3 membranes.
thylakoid membranes in stacks in addition to inner and outer
protons pumped through thylakoid lumen instead
stroma
space between thylakoid and inner membrane
whats product of carbon fixation (calvin cycle)?
GAP
GAP converted into hexose sugar to use as chem nrg at night
proton pumping
protons pumped to lumen of thylakoid
protons build up here and exit thylakoid through ATP synthase
ATP synthesized in stromal space
all used in calvin cycle (which is in also in stroma?)
which is analogous to he thylakoid membrane: the inner mitochondrial membrane or outer mitochondrial membrane?
inner
Flourescence
e- is excited, and then returns to ground state
nothing really accomplished
resonance energy transfer
one chlorophyl transfers its energy to another chlorophyl
exited state passed down the line
e- from first returns to ground state, but another molec has been exciting
photooxidation
e- is in excited state
redox reaction
water oxidized, pheo molec reduced
THIS IS WHAT NEEDS TO HAPPEN FOR NRG TRANSFER
Z scheme
e- start on water move to PSII photon absorption excites e- photoox happens PSI more photons absorbed photoox e- goes to 2NADP to make 2NADPH
how many photons of light to take 4 e- from water?
8! 1 photon to excite every electron at both PSII and PSI
it happens one at a time
What is PC (plastocianin) similar to?
cytochrome C
