topic 6 - phototrophic metabolism - photosynthesis Flashcards
how do reaction centres reduce a primary e- acceptor
- light is absorbed by an antenna pigment
- energy is transferred by inductive resonance to a reaction centre
- e- is excited as a reaction centre and is transferred to a primary e- acceptor
what happens in photosystem II
energy from photons channels through antenna pigments to reduced P680
e- is excited in P680* (excited form)
transfer e- to primary e- acceptor
P680+ (oxidised)
how to get P680+ (oxidised) back to P680
e- donated from water is used to reduce P680+
allows the cycle to continue
what is the difference in H+ concen between stroma and thylakoid lumen
stroma = low concen of H+ (higher pH)
thylakoid lumen = high concen of H+ (low pH)
what is plastoquinone (PQ)
hydrophobic e- taxi
- when reduced (gains e-) it also gains an a proton from the stroma
what is plastocyanin (PC)
hydrophilic e- taxi
how does photosystem II produce PMF
energy from light goes to P680
P680 reduces its PEA which passes the e- to PQ which gains a proton from the stroma
PQ reduced the cytochrome complex and releases a proton in the lumen (building H+ concen in lumen)
cytochrome reduces plastocyanin that passes e- to P700+ (oxidised)
what happens in photosystem I
P700 is initially reduced
receives energy through inductive resonance and e- on P700 is excited to P700*
e- transferred to PEA
P700 oxidised to P700+
how does P700+ get reduced back to P700
e- to reduce comes from plastocyanin in PS II
how does PS I produce NADPH
P700 reduces the PEA which passes the e- to ferrodoxin
NADP+ reductase reduces NADP+ to NADPH in the stroma
where/what is ferrodoxin
on stroma side of thylakoid membrane (peripheral protein)
hydrophilic e- taxi that reduces NADP+ reductase
how is PMF generated through photosystems across the thylakoid membrane
protons in the stroma are used to reduce NADP+ to NADPH (lower H+ concen in the stroma)
oxidation of water in the lumen releases protons
PQ moves protons from the stroma to the lumen
what occurs during photophosphorylation
using solar energy to generate PMF to power ATP synthase
ATP generated on the stroma side of the thylakoid
takes a lot of energy to oxidise water and reduce NADP+
what is the role of PS II and PS I in oxidising water and reducing NADP+
PS II - excites e- enough to pull e- from water and generate PMF but not enough to reduce NADP+
PS I - role is to re energise the e- in order to reduce NADP+ (uses second photon of light to re energise the e-)
where does the calvin cycle occur
stroma (space in chloroplast surrounding thylakoids)
what is the calvin cycle
11 reactions - each reaction is catalysed by an enzyme
highly endergonic overall - building carbs from CO2 requires a lot of input of energy from ATP and NADPH from light reactions
each individual reaction is exergonic because they are coupled with the oxidation of NADPH and ATP hydrolysis
what are the phases of the calvin cycle
phase 1 - fixation / carboxylation
phase 2 - reduction (requires energy)
phase 3 - regeneration (requires energy)
cycle goes around 3 times
what happens during phase 1 of the calvin cycle
3 molecules of CO2 enter
react with 3 RuBP (5C molecule) with enzyme rubisco
combine 15 C atoms from RuBP with 3 from CO2 to make 6 3C molecules (18C total) of 3PGA
what happens in phase 2 of the calvin cycle
reduce the C molecules
3PGA will become progressively more reduced
input = 6 ATP and 6 NADPH (for energy)
6 3PGA into 6 G3P
(one G3P released)
what happens during phase 3 of the calvin cycle
need to make RuBP for the next cycle
input = 3 ATP (for energy)
have 5 G3P
what is the total input into the calvin cycle
9 ATP
6 NADPH
(for 3 cycles)
what is the purpose of cyclic e- transport
produces ATP without the synthesis of NADPH (supplies additional ATP for the calvin cycle)
calvin cycle needs more ATP than NADPH
cyclic e- flow allows it to stop making NADPH by making PMF to power ATP synthesis
what happens during cyclic e- flow
e- will flow from PQ to P700 in a circle to generate PMF to make ATP
ferrodoxin can reduce PQ instead of NADP+ reductase
how much is linear and cyclic e- flow used
80% of photosynthetic ETC use linear e- flow
20% use cyclic
what is the product of photosynthesis
G3P
what does G3P turn into
converted to glucose
3C molecule so need 2 to make 1 glucose
what is glucose used for
used for glycolysis in the cytoplasm
linked into polymers of starch / cellulose (if the cell has enough energy)
- starch = energy storage
- cellulose = cell wall
used for synthesis of other biomolecules
