Re: I need SIMPLIFIED information about what happens during the CALVIN CYCLE

The end result of the Calvin-Benson Cycle, also called the Calvin Cycle, C3 
Cycle, and Carbon Reduction Cycle, is that carbon dioxide gas (CO2) is fixed as 
a carbohydrate, such as sucrose or starch. Melvin Calvin won the 1961 Nobel 
Prize in Chemistry for the Calvin-Benson cycle. Calvin was the head scientist, 
but many other scientists made important contributions to the research 
including Andy Benson. 

The Calvin-Benson Cycle requires the ATP and NADPH produced in the light 
reactions of photosynthesis for energy and elections. The Calvin-Benson Cycle 
is often called the dark reactions of photosynthesis but that is a misnomer 
because the Calvin-Benson Cycle occurs in the light, not at night. The Calvin-
Benson Cycle takes place in the stroma of the chloroplasts.

The Calvin-Benson Cycle starts when a 5-carbon sugar (ribulose bisphosphate) 
combines with one CO2 to form a 6-carbon compound which immediately breaks down 
to form two, 3-carbon molecules (3-phosphoglyceric acid or PGA). The enzyme 
that catalyses this first step is ribulose bisphosphate carboxylase oxygenase 
(RUBISCO). RUBISCO is considered the most abundant protein on earth.
 
For every six CO2 fixed, there are thus twelve, 3-carbon PGAs. Two of those can 
be siphoned off to form glucose or fructose, which is used to synthesize starch 
or sucrose. Large starch grains often form in chloroplasts in the light. The 
remaining ten, 3-carbon PGAs go through a series of enzymatic reactions that 
regenerate the six, 5-carbon sugars that the cycle started with. This allows 
the cycle to repeat.

References


Photosynthesis: Pathway of Carbon Fixation


1961 Nobel Prize in Chemistry


Calvin-Benson Cycle