Photosynthesis Flashcards
Where does light dependent reaction occurs?
In the thylakoid stacks inside the chloroplast
Where does light independent reaction occurs?
What is the name of the cycle that happens here?
In the stroma of the chloroplast.
Calvin cycle.
Where photo systems are found?
In the thylakoid membrane.
What happens in photosystem 2?
1) It receives photons from light.
2) Energy from light goes on the chlorophyll reaction center where a pair of electrons is excited/energised.
3) Energised electrons escape photosystem 2 to an electron acceptor.
What happens in photosystem 2 after electrons escaped?
Photolysis inside the thylakoid membrane results in 2H+ + 1/2O2 + 2es. The 2 electrons from this reaction go to photosystem 2 in order to replace the escaped electrons.
What do electrons do when they move along electron transport chain?
They release energy which creates hydrogen ion gradient.
What happens with hydrogen ions which are in the stroma?
Protein in electron transport chain pumps H+ into the thylakoid space.
What do the H+ ions do in the thylakoid space?
They move down the concentration gradient through ATP synthase in the stroma releasing energy.
What is the point of H+ ions moving through ATP synthase?
H+ ions release energy which ATP synthase uses in order to add phosphate molecules to ADP to form ATP.
What happens after H+ ions moved through ATP synthase?
The photosystem 2 absorbs additional energy from the light so a pair of new electrons formed by photolysis escapes photosystem 2 and moves along the electron transport chain. At the same time 2 electrons are added to photosystem 2 from photolysis.
What happens to the 2 electrons which remained in photosystem 1 since the time they were transported from photosystem 2?
These 2 electrons leave the photosystem 1 into the stroma where together with H+ they reduce NADP+ into NADPH.
What are the main 3 steps of Calvin cycle?
1) carbon dioxide fixation
2) carbon dioxide reduction
3) regeneration of RuBP
What happens during carbon dioxide fixation?
CO2 from the air attaches to a 5 carbon molecule called RuBP together with the rubisco enzyme.
As a result, an unstable 6 carbon molecule is formed.
But it quickly breaks up into 2 parts called 3-phosphoglyceric acid (3PG).
What happens during carbon dioxide reduction?
2 ATP are changed to 2 ADP. 2 phosphates from 2ATP are added to 2 molecules of 3-phosphoglycerate (1P to one 3-PG). Now, the name of these molecules is 1,3-bisphosphoglycerate.
The 1,3-bisphosphoglycerate molecules are reduced (gain electrons). The molecules gain 2 electrons from conversion of NADPH and loses on phosphate group. After the addition of electrons and loss of phosphate groups, we have 2 molecules called glyceraldehide-3-phosphate.
By products are 2NADP+ and 2 phosphates.
2 ADP and 2 NADP+ are then reused in light-dependent reaction.
What happens during regeneration phase?
One glyceraldehyde-3-phosphate molecule goes to make glucose while another one should go to restore RuBP. But one G3P molecule is not enough to restore RuBP and so the cycle occurs 3 times. Also, without a process being repeated 3 times, 1 G3P molecule wouldn’t be able to leave to make glucose.
This step requires 1 ATP molecule!!!
