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explain the steps of dark reaction.

Dark reaction of photosynthesis is completed in three stages:
1. Carboxylation: In this step, carbon dioxide is added to ribulose-1,5-bisphosphate in the presence of rubisco enzyme and forms two molecules of 3-phosphoglyceric acid. 
2. Glycolytic reversal: In this step, 3-phosphoglyceric acid is converted into glucose through various steps which are reversal of the steps found during glycolysis part of respiration.
3. Regeneration of RuBP: In this RuBP is regenerated and is ready to accept another molecule of carbon dioxide. 

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1. A five-carbon sugar molecule called
ribulose bisphosphate, or RuBP, is the
acceptor that binds CO2 dissolved in
the stroma. This process, called CO2
fixation, is catalyzed by the enzyme
RuBP carboxylase, forming an
unstable six-carbon molecule. This
molecule quickly breaks down to give
two molecules of the three-carbon 3-
phosphoglycerate (3PG), also called
phosphoglyceric acid (PGA).
2. The two 3PG molecules are
converted into glyceraldehyde 3-
phosphate (G3P, a.k.a.
phosphoglyceraldehyde, PGAL)
molecules, a three-carbon sugar
phosphate, by adding a high-energy
phosphate group from ATP, then
breaking the phosphate bond and
adding hydrogen from NADH + H+.
3. Three turns of the cycle, using three
molecules of CO2, produces six
molecules of G3P. However, only one
of the six molecules exits the cycle as
an output, while the remaining five
enter a complex process that
regenerates more RuBP to continue the
cycle. Two molecules of G3P, produced
by a total of six turns of the cycle,
combine to form one molecule of
glucose.
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