Explanation:
Serine threonine, tyrosine in eukaryotes and also histidine in prokaryotes and plants are the most typically phosphorylated amino acids (though it is now known to be common in humans). These phosphorylations have crucial and well defined functions in the pathways of signalling and metabolism.
Phosphorylation is the most frequent process of protein function regulation and cellular signal transmission. While phosphorylation in bacterial proteins has been seen, in eukaryotic cells it is far more prevalent.
