Photosynthesis Flashcards
(24 cards)
what is the substructure of the chloroplast?
photosynthesis takes place in chloroplasts
outer envelope membrane
inner envelope membrane
thylakoid membrane are continuous with appressed membranes grana
lamellae these are non-appressed regions
grana
inner/inter membrane space
thylakoid lumen
stroma - separate impermeable barrier and biochemically distinct
how does chloroplast structure enable electron transport and the production of ATP/NADPH?
what is the role of the pigments and what wavelengths are important?
photosynthetic pigments may absorb light at more than one wavelength
pigment a - 420660nm - all higher plants and algae
pigment b - 435643nm - all higher plants and green algae
pigment c - 445625nm - diatoms and brown algae
pigment d - 450690nm - red algae
what is the ‘resonance energy transfer’ and how does it feature in photosynthesis?
the energy absorbed excites the electrons in the chlorophyll molecule - have a high reducing power
this is the photon transferring energy from one pigment to the next from the donor to the electron acceptor to allow the electron to return for a ground state
energy is focused onto a reaction centre - in photosystem II on P680 or photosystem I to P700 (also called special pair of chlorophylls)
the donor is reduced and the acceptor is oxidised using high energy electrons
what happens to the electrons during electron transport?
after electrons to a high electron state, the electrons will allow the electron donor to be oxidised and the electron acceptor to be reduced
how is the electron in P680 replaced?
the electron donor is from water using the Z-scheme of electron transport - 2H2O -> 4e- + O2 + 4H+
the use of the manganese cluster or the oxygen evolving centre catalyses the splitting of water
P680 - electrons excited passes to pheophytin to bound plastoquinone A to then plastoquinone B to then soluble plastoquinone
what is the role of cytochrome b6f complex, and how does it increase the proton gradient?
creates a docking site for plastoquinone and plastoquinol
create a proton gradient to produce ATP as H+ is pumped through ATP synthase
what is the fate of the electrons from the electron transport and the proton gradient?
plastoquinol which is a plastoquinone with two electrons and two proton attached
binds at luminal side
splits itself into three part, two electrons, two protons which get expelled into the lumen and plastiquinone which floats away on the membrane
iron sulphide passes one electron to water soluble to plastocyanin
other electrons is passed to another plastiquinone molecule which makes it slightly negatively charged
produces 6H+ which produces a potential difference between the lumen and the stroma
what is the difference in energy state of PSI and PSII?
PSI has a higher energy state than PSII on the z-scheme
plastocyanin
aids the transport to PSI
Cu+ core which is easily reduced and plastocyanin docks with PSI so that the electrons can then be transferred to ferredoxin
ferredoxin
iron-sulphur compound
the electrons which are transferred are used to make NADPH (reducing power)
what does NADP+ reductase comprise of? and what is its function?
ferredoxin-NADP+ reductase and FNR
allows the production of NADPH
the role of the thylakoid structure in regulating PSII and PSI function
thylakoid membrane are in lines or stacks
PS1 needs more interaction with the stroma
PS2 is happier in the stacked bits of the membrane
they need to work in balance to each other, this is regulated by light harvesting complex II (lipid soluble, can bind to both PSI and PSII)
function of light harvesting complex II
different activities of each photosystem throughout the day which needs to be balanced
increased amount of reduced form
upregulate PSI to activate LHC2 kinase
pulls away from PSII and instead goes to PSI to upregulate that (dephosphorylates) and vice versa
NADPH and ATP used for
drives calvin-benson cycle
used to create carbohydrate compounds
ATP synthesis
into a subunit
pushes c subunit out the way
drives gamma subunit
beta subunit change shape
carbon reactions process
- carboxylation - this is carbon fixation using Rubisco (enzyme which catalyses the process) and CO2 combine (6C - 3C)
- reduction - 3C is then reduced to make it easer to turn into carbo using NADPH and ATP to aid this regulated by phosphoglycerate phosphate which is self regulating then still needs to be reduced using GAP dehydrogenase by using NADH electrons (essentially goes through a sequences of reduction reactions) producing 18C
- regeneration - triose phosphate isomerase (triose phosphate) used to create carbo, fate differs so can produce sucrose if too much sucrose starch is produced, starch inside chloroplast, sucrose outside the chloroplast and inside the cytoplasm
rubisco structure and function
16 subunits
8 large - catalytic in pairs at top and tail
8 small - structural acting as glue
synthesised in different parts of the cell using TOC and TIC complexes
transported across the two membranes (large)
regulated by light - by rubiscoactivase
used for carboxylation - carbon fixation
uses oxygen instead of CO2 which has no positive use - wasteful (glyoxylate cycle - involved phoshoglycerate)
triose phosphate antiporter
swaps triose phosphate out for inorganic phosphate in
sucrose need decreases so less conversion to sucrose and Pi drops
RuBP where does it come from?
it is regenerated
which enzymes are regulated by light?
Rubisco
GAPDH
PRK
FBPase
aldolase
SBPase
when is carboxylation favoured?
at low temperatures
alternative photosynthetic pathways
C3 photosynthesis - linked to gas exchange
C4 photosynthesis - dissociated from gas exchange - two different types of chloroplast containing cells in mesophyll and bundle sheath
CAM photosynthesis - gas exchange only at night - reduces water loss
