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.

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    $\begingroup$ 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. $\endgroup$ – WYSIWYG Jun 11 '15 at 10:39

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

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  • $\begingroup$ 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 '15 at 7:19
  • $\begingroup$ Yes, this is incorrect. Synthesis of ATP is usually referred to as "ATP synthesis". $\endgroup$ – Chris Jun 11 '15 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 '15 at 13:28
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    $\begingroup$ Also substrate level phosphorylation… $\endgroup$ – canadianer Jun 11 '15 at 17:01
  • $\begingroup$ Oxidative phosphorylation is a mechanism that aerobic cells use to make ATP. As canadianer eludes to, ATP may also be 'made' by substrate-level phosphorylation. This is what happens in glycolysis, where the pyruvate kinase reaction is a good example of substrate-level phosphorylation 'making' ATP. $\endgroup$ – user1136 Jul 16 '15 at 18:17

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