L6 photosynthesis part 2 Flashcards
everything happens inside the…. and in the … in particular
chlorplast
thylakoid membranes
what is on the surface of the thylakoid membrane?
-pigment molecules (chlorophyll a and b and carotenoids)
-embedded in thylakoid, in association with proteins
how are pigment molecules organized on the thylakoid membrane?
in discrete membranes, photosystems
how many pigments do photosystems each carry?
approx. 250-400 pigments
what are the two components of the photosystems?
antenna complex and reaction center
photosystems are surrounded by … (ones without reaction centers)
many light-harvesting complexes
photosystems + light-harvesting complexes = ….
photosystem complex
what is resonance energy transfer?
energy moving from one pigment to the next
what is chlorophyll a’s role?
to absorb energy and boost electrons to a higher energy level, which initiates energy flow
i.e., chlorophyll a becomes oxidized
photosynthesis occurs between two ….
photosystems, photosystem I (P700) and photosystem II (P680). they work simultaneously
what are PSI and PSII linked by
the electron transport chain
what happens in photosystem II?
water is oxidized to oxygen. water is split into hydrogen protons and oxygen molecules. two electrons are stripped and passed onto the complex. these electrons replaces the electrons that are lost by the reaction center, p680
what is the PSII complex made up of?
an intricate network of manganese, oxygen, and calcium ions, that strip electrons off water. this intricate network is embedded in the psII protein complex, located at the base of the photosystem, facing the thylakoid lumen
explain the process that occurs in PSII (P680)
light energy is absorbed by chlorophyll a in reaction center, exciting electrons. the excited electrons are then passed on to the electron acceptor, known as pheophytin. the electron transport chain then follows. This entails electrons being passed thorugh plastoquinone (Qa) and plastoquinone (Qb), to the Cyt b6/f complex
what is pheophytin?
modified chlorophyll a molecule, magnesium atom replaced by two protons
how many protons does Plastoquinone B (PQb) picks up?
two protons
how are electrons and protons moved thought the Cyt b6/f complex?
2 electrons are donated to the complex (one at a time), and 2 protons are funelled into the lumen. reduced cytochrome f donates electrons to plastocyanin
what happens in photosystem I?
light energy excited antenna molecules, A0 being the primary acceptor where electrons are then passed downhill on the stromal side of the membrane. the final acceptor is Ferredoxin (mobile iron-sulfur protein). NADP+ is reduced to NADPH
summary of what happens between PSII and PSI:
electrons flow continuously from PSII and PSI, ultimately to NADP+, oxidation of water, reduction of NADP, a non-cyclic electron flow
PSII supplies electrons for PSI, with 6 electrons at each turn, producing 6 ATP + 6 NADPH
what is cyclic phosphorylation?
a process that bypasses PSII. electrons excited in PSI pass through cascade to cytochrome complex, on to plastocyanin and back to PSI. protons are pumped into the lumen which drives ATP synthesis
what is cyclic phosphorylation necessary for?
carbon fixation (3:2 ratio of ATP to NADPH)
what does the ATP synthase complex do?
releases protons into thylakoid membrane during the oxidation of water via the cytochrome b6/f complex. this generates an electrochemical proton gradient (lumen:stroma)
part of photo-phosphorylation
