# The Calvin Cycle --- The **Calvin cycle** is a process that happens in plants during [[photosynthesis]] that fixes CO$_2$ into a usable form. First a CO$_2$ molecule is attached to a 5-carbon "ribulose bisphosphate", in a reaction catalyzed by the enzyme "rubisco". Also referred to as the "light independent reactions", as the Calvin cycle does not require sunlight directly, but only the stored energy created during the [[light dependent reactions]]. ## Products G3P is basically always turned into glucose and fructose. ## Location The Calvin cycle takes place in the [[chloroplast.png|stroma]] of the choloroplast. ## The Things We Need 3PGA - 3-phosphoglyceric acid G3P - Glyceraldehyde 3-phosphate, also used in glycolysis. RuBP - Ribulose 1,5-bisphosphate To power the Calvin cycle we also need ATP and NADPH, both of which are generated from the [[ETC (chloroplast)|ETC]]. ### Rubisco The protein **rubisco**, which is incredably common if ineffecient. Additionally O$_2$ will also bind to it's active site, which not only takes away a chance for the CO$_2$ to bind, but it basiclly "undoes" photosynthesis, in a process called "photorespiration". To make up how inefficient it is, plants just make a lot of it to compensate. It is regulated by the relative concentrations of CO$_2$ and O$_2$ ## Phases of The Calvin Cycle ### The Fixation Phase In the **fixaction phase**, CO$_2$ reacts with RuBP and produces 2 3PGAs. ### The Reduction Phase In the **reduction phase** the 3PGA is phosphorylated by ATP and reduced by NADPH to produce 3 G3Ps. ### The Regeneration Phase In the **regeneration phase** the remaining 3PGAs are used to regenerate the RuBP Every 3 times the cycle goes around, it produces 1 3-carbon sugar. ![[calvin cycle.png]] ___