Final answer:
Serine, threonine, and tyrosine can be phosphorylated due to their polar hydroxyl (-OH) groups, facilitating attachment sites for phosphate groups.
Step-by-step explanation:
The amino acids serine, threonine, and tyrosine can be phosphorylated because they contain a hydroxyl (-OH) group. This group serves as the attachment site for phosphate groups during the process of phosphorylation, a key mechanism in cellular signaling pathways.
The presence of this hydroxyl group makes these amino acids polar, which contributes to their solubility in water and enables them to participate in hydrogen bonding. Moreover, the side chains in these amino acids are polar but uncharged, which allows for specific interactions necessary for various biological functions, including protein regulation through phosphorylation.