Theme 2 - Part C Flashcards Preview

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Flashcards in Theme 2 - Part C Deck (11):

What is meant by "carbon fixation"?

Conversion of CO2 into organic forms (reduction reaction with electrons - and protons - being added to CO2)


What is the fluid within the thylakoid called? The fluid surrounding the thylakoids?

lumen; stroma


What is the difference between P680, P680* and P680+?

P680 is the specialized chlorophyll a in the reaction centre of photosystem II, which absorbs light maximally at 680 nm. When P680 is excited, it is denoted as P680*. In this excited state, it can be easily oxidized by the primary electron acceptor to form P680+.


What facilitates electron flow between each of the following?
1) photosystem II to cytochrome complex
2) cytochrome complex to photosystem I

1) plastoquinone
2) plastocyanin


How is the proton gradient across the thylakoid membrane achieved?

1. Protons are transferred to the lumen through the cyclic oxidation and reduction of plastoquinone as it migrate between photosystem II and the cytochrome complex.
2. Protons are added to the lumen through the oxidation of water producing 2H+, which occurs on the luminal side of photosystem II.
3. H+ removed from the stroma by NADP+ reductase to make NADPH contributes to the proton gradient across the thylakoid membrane.


How many photons of light are needed to move one electron down the ETC?

2; one absorbed by PSII and another by PSI.


What occurs in cyclic electron transport? Why is it necessary?

Photosystem I operates without involvement of PSII. After electrons are transferred to ferrodoxin, they are not donated to NADP+ reductase. Instead, they are returned to the plastoquinone pool, allowing PQ to get continuously reduced and oxidized. This continues the flow of protons across the thylakoid membrane and build-up of PMF, which ultimately drives the synthesis of ATP.
The reduction of CO2 by the Calvin cycle requires more ATP than NADPH; this difference is made up for through cyclic electron transport.


What is produced in the fixation stage of the Calvin cycle? (Respond for 3 turns of the cycle)

produced: 6 molecules of 3-phosphoglycerate


In the reduction stage of the (3 rounds of) the Calvin cycle, how many molecules of ATP and NADPH are used? What is produced?

6 G3P produced


What is the most abundant enzyme in the biosphere? What is its function? Why must it be so abundant?

Rubisco; it catalyzes the fixation of CO2 into organic form within the Calvin cycle.
It is abundant because it is catalytically very slow.


Why is NADPH required in the Calvin cycle?

It acts as a reducing agent, adding electrons to 1,3-bisphosphoglycerate to produce G3P.