Where is ATP used in Phosphorylation? In the section describing the Calvin Cycle, under the subheading "Reduction", my textbook states that: > The steps involve utilisation of 2 molecules of ATP for Phosphorylation... I could not get where is ATP used in Phosphorylation (ATP synthesis by cells)? Please help me to understand.

In biology phosphorylation marks the addition of inorganic phosphate groups to proteins or other organic molecules. The phospho-group usually comes from ATP which is converted into ADP in this process.

In the context of the Calvin Cycle there are two positions where molecules get phosphorylated. The first is the phosphorylation of 3-phosphogylcerate to 1,3-bisphosphoglyerate, the other is the phosphorylation of Ribulose 5-phosphate to Ribulose 1,5-bisphosphate.

See the image (from here):

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