Question

The amino acids tyrosine, threonine and serine all have side chains which contain hydroxyl groups. Explain why this feature makes these amino acid residues important in the regulation of metabolism, cell growth and cell differentiation.  

Answer 1

Of the 20 amino acids, only serine, threonine, and tyrosine contain the proper functional group (hydroxyl moiety, OH) to accommodate phosphorylation.

Phosphorylation on amino acids, such as serine, threonine, and tyrosine results in the formation of a phosphoprotein, when the phosphate group of the phosphoprotein reacts with the -OH group of a Ser, Thr, or Tyr sidechain in an esterification reaction

Phosphorylation by protein kinases is recognized as a critical mechanism by which virtually every activity of eukaryotic cells is regulated, including proliferation, gene expression, metabolism, motility, membrane transport, and apoptosis.