Explain the three phase of Dark reaction .

Explanation

Phase 1 - Carboxylation (Fixation).
The acceptor molecule Ribulose 1,5 Bisphosphate (RUBP) a 5 carbon compound with the help of RUBO carboxylase oxygenase (RUBISCO)enzyme accepts one molecule of carbons dioxide to from an unstable 6 carbon compound. This 6C compound is broken down into two `RUBP + CO_(2) overset("Rubisco")to 2" molecules PGA"`
Phase 2 - Glycolytic Reversal / Reduction .
Phospho glyceric acid is phosphorlyation by ATP and produces 1,3 bis phospho glyceric acid by PGA kinase . 1,3 bis phospho glyceric acid is reduced to glyceraldehyde 3 Phosphate (G-3-P) by using the reducing power `NADPH + H^(+)`. Glyceraldehyde 3 phosphate is converted into its isomeric form dihydroxy acetone phosphate (DHAP).
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Phase 3 - Regeneration : Regeneration of RUBP involves the formation of several intermediate compounds of 6 - carbon, 5 - carbons ,4 - carbon and 7 - carbon skeleton . Fixation of one carbon dioxide requires 3ATPs and 2 NADPH `+ H^(+)` , and for the fixation of `6 CO_(2)` requires 18 ATPs and 12 `NADPH + H^(+)` during `C_(3)` cylce. One 6 carbon compound is the net gain to form hexose sugar.