Protein modifications refer to the covalent attachment of specific chemical groups to proteins, which can alter their structure, stability, and function. These modifications can include phosphorylation, glycosylation, acetylation, ubiquitination, and methylation, among others. Protein modifications play crucial roles in various cellular processes such as signal transduction, protein trafficking, and gene expression regulation. Studying protein modifications is essential for understanding the complex regulatory mechanisms that govern cellular function and dysfunction, and is therefore an important area of research in molecular biology and biochemistry.