Nucleotide (phosphorylation): mechanism and explanation
The primary 5′-OH group of the nucleoside is esterified with phosphate: adenosine becomes adenosine monophosphate (AMP), a nucleotide.
Example
The kinase transfers the terminal phosphate group of ATP to the 5′-OH group. Chemically this is a phosphoric acid ester, the counterpart of a carboxylic ester.
Mechanism step by step
- 1
The kinase binds the nucleoside and ATP (with Mg²⁺ shielding the negative charges).
- 2
The 5′-OH group attacks the γ-phosphorus of ATP (nucleophilic substitution at P).
- 3
ADP leaves and the 5′-monophosphate (nucleotide) forms.
To read
This topic is part of the syllabus but not in the training: polymers consist of repeating units and biomolecules react through enzymes in the cell. There is no clear-cut task with exactly one product for it.
Go to the trainer with 157 reactions to practiseFrequently asked questions
Why is ATP energy-rich?
The phosphoric anhydride bonds suffer charge repulsion, and the hydrolysis products are better solvated and resonance-stabilised. Transferring a phosphate group therefore releases energy.
Why is phosphate negatively charged at pH 7?
The P–OH groups are acidic (pKa ≈ 1 and 6). The negative charges make nucleic acids water-soluble and protect the ester bonds from hydrolysis by hydroxide.