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.

  • 2
    $\begingroup$ This is a homework question. Even though you got your answer, please put in some effort on your part before asking a question. It is a good practice for everyone. $\endgroup$
    Jun 11, 2015 at 10:39

1 Answer 1


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):

enter image description here

  • $\begingroup$ Thanks for the help! so is it incorrect to say that phosphorylation is synthesis of ATP (since you said that the ATP is converted into ADP in this process)? $\endgroup$
    – Abdullah
    Jun 11, 2015 at 7:19
  • $\begingroup$ Yes, this is incorrect. Synthesis of ATP is usually referred to as "ATP synthesis". $\endgroup$
    – Chris
    Jun 11, 2015 at 7:20
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    $\begingroup$ @Abdullah, perhaps your confusion about the meaning of 'phosphorylation' in relation to ATP synthesis is because you may have previously learned of a process called 'oxidative phosphorylation' (sometimes abbreviated to OxPhos, or similar) that occurs downstream of the Kreb's Cycle--and is a mechanism cells use to synthesize ATP? Just a thought. The typical and predominant usage in lectures, textbooks, and papers is in Chris's answer that you accepted. The acid anhydride ATP donates its gamma phosphate to some other molecule in a reaction catalyzed by an enzyme. $\endgroup$
    – mdperry
    Jun 11, 2015 at 13:28
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    $\begingroup$ Also substrate level phosphorylation… $\endgroup$
    – canadianer
    Jun 11, 2015 at 17:01

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