Final answer:
Phosphorylation of proteins can alter gene expression by activating or inactivating enzymes, creating binding sites for downstream signaling molecules, or affecting protein stability and degradation.
Step-by-step explanation:
Phosphorylation is a common chemical modification that adds a phosphate group to a protein. This modification can alter gene expression by activating or inactivating enzymes, creating binding sites for downstream signaling molecules, or affecting the stability and degradation of the protein. For example, phosphorylation of serine and threonine residues can activate enzymes, while phosphorylation of tyrosine residues can both affect enzyme activity and create binding sites for downstream components in a signaling cascade.