`star` Steps in Calvin Cycle
`star` Carboxylation
`star` Reduction
`star` Regeneration


● `color{Brown}"Calvin and his co-workers"` then worked out the `color{violet}"whole pathway"` and showed that the pathway operated in a `color{violet}"cyclic manner"`; the `color{violet}"RuBP was regenerated."`

● Is important to understand at the outset very clearly that the `color{violet}"Calvin pathway"` occurs in `color{violet}"all photosynthetic plants"`; it does not matter whether they have `C_3` or `C_4` (or any other) `color{violet}"pathways"`.

● For ease of understanding, the `color{violet}"Calvin cycle"` can be described under `color{violet}"three stages"`: `color{Brown}"carboxylation, reduction"` `color{Brown}"and regeneration"`.


● `color{Brown}"Carboxylation"` is the `color{violet}"fixation"` of `CO_2` into a `color{violet}"stable organic intermediate"`.

● Carboxylation is the `color{violet}"most crucial step"` of the Calvin cycle where `color{violet}"CO_2` is utilised for the `color{violet}"carboxylation of RuBP."`

● This reaction is catalysed by the `color{violet}"enzyme RuBP carboxylase"` which results in the formation of `color{violet}"two molecules"` of `color{violet}"3-PGA"`.

● Since this enzyme also has an `color{violet}"oxygenation activity"` it would be more correct to call it `color{Brown}"RuBP carboxylase-oxygenase"` or `color{Brown}"RuBisCO"`.


● These are a `color{violet}"series of reactions"` that lead to the `color{violet}"formation of glucose"`.

● The steps involve utilisation of `color{violet}"2 molecules of ATP"` for phosphorylation and `color{violet}"two of NADPH"` for `color{violet}"reduction"` per `CO_2` molecule fixed.

● The fixation of `color{violet}"six molecules"` of `CO_2` and `color{violet}"6 turns of the cycle"` are required for the removal of `color{violet}"one molecule of glucose"` from the pathway.


● `color{violet}"Regeneration"` of the `CO_2` `color{violet}"acceptor molecule RuBP"` is crucial if the cycle is to continue uninterrupted.

● The regeneration steps require `color{violet}"one ATP for phosphorylation"` to form RuBP.

● Hence for every `CO_2` molecule entering the `color{violet}"Calvin cycle"`, `color{violet}"3 molecules of ATP"` and `color{violet}"2 of NADPH"` are required.

● It is probably to `color{violet}"meet this difference"` in number of `color{violet}"ATP and NADPH"` used in the dark reaction that the `color{violet}"cyclic phosphorylation"` takes place.

● To make `color{violet}"one molecule of glucose"` 6 turns of the cycle are required.

● So we can calculate the `color{violet}"ATP and NADPH"` molecules will be required to make `color{violet}"one molecule of glucose"` through the Calvin pathway.

● It might help if we look at what `color{violet}"goes in and"` `color{violet}"what comes out"` of the Calvin cycle.