Protein modification refers to the chemical changes that occur to proteins after they are synthesized. These modifications can include the addition of functional groups, such as phosphate or methyl groups, which can alter a protein's activity, stability, or location within a cell. Common types of modifications include phosphorylation, glycosylation, and ubiquitination. These modifications play a crucial role in regulating various biological processes, including cell signaling, metabolism, and gene expression. By modifying proteins, cells can respond to changes in their environment and maintain homeostasis. Understanding protein modification is essential for fields like biochemistry and molecular biology.