Photosynthesis is a process that happens in plants and bacteria that allows them to make their own energy. This process also provides energy for every other organism on earth. More specifically, it happens in the chloroplasts of plants. Chloroplasts are special cells in plants that have 2 membranes, and are made up of stacks of thylakoids (granum). The thylakoid contains chlorophyll, which is a catalyst. It is in the thylakoid where light is used to produce ATP and NADPH (energy carrying molecules).
Photosystem II absorbs light with wavelengths of 680nm, in doing that, it splits a water molecule and takes its electrons in a process called hydrolysis(leaving 2 protons and an oxygen ion). The electrons make it down the electron transport chain, leaving redox reactions in its wake.
The electrons are passed to PQ (plastoquinone), PSII oxidizes and PQ reduces. Then, from PQ, the electrons travel to B6F, and a portal is created for hydrogen ions to flow out of the thylakoid membrane. Then they are passed to PC, but before they can be passed to Photosystem I, PSI must be struck by light of 700mn.
From PSI, the electrons are passed to FD and FNR. FNR then passes them to NADP+ to make NADPH. This entire process continues as long as there is an abundant amount of both water and sunlight.
(PSII > PQ > B6F > PC > PSI > FD > FNR > NADP+ > NADPH)
The hydrogen that were transferred through PQ and B6F cause an imbalance of pH on either side of the membrane. This causes the H+ ions to go back into the chloroplast stroma through the ATP synthase, in a process called chemiosmosis. This allows ADP to be converted into ATP (by adding a third phosphate). This entire process is known as the non-cyclic light dependent reaction and it happens in eukaryotic cells.
Prokaryotes use the cyclic light dependent reaction which only consists of B6F, PSI, FD, and FNR, and electrons are returned to B6F again, and again (creating the electron portal). In this process, however, NADPH is not made, and ATP is used directly, instead of making glucose.
CALVIN CYCLE (LIGHT INDEPENDENT)
The light independent does not use energy from the light, but rather the energy from ATP (which is made from the light dependent reaction).
The Calvin Cycle begins with carbon fixation, a process where carbon dioxide reacts with RuBP (ribulose biphosphate) and produces 2 strands of PGA, each with 3 carbons, since carbon chains with more than 6 carbons are unstable. This reaction is catalyzed with rubisco.
A phosphate from ATP is added to each PGA, changing it into BPG, and the two ADPs go back to the light dependent reaction to be reconverted into ATP. Then, a phosphate group is removed from BPG by NADPH, in that process, a hydrogen from NADPH is lost, and NADP+ also goes back to the thylakoid to be reconverted into NADPH. The compounds that are formed from the loss of phosphate are G3P. The two G3Ps formed can combine (with the help of a reshaping enzyme) to make one molecule of glucose.
The results from one cycle of the Calvin cycle are as follows: 3 RuBPs catalyzed > 6 PGAs made > 6 BPGs > 6 G3Ps
5 of the 6 G3Ps are recycled through a series of reactions and becomes RuBP to go through the cycle again, and 1 of them makes it out of the cycle. Therefore, it takes two Calvin cycles to make one molecule of glucose.
OVERALL REACTION
6CO2 + 6H2O -[light and chlorophyll]-> C6H12O6 + 6O2
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