Protein modification refers to the chemical alterations that proteins undergo after they are synthesized in a cell. These modifications can include processes such as phosphorylation, glycosylation, acetylation, and methylation, among others. Protein modifications play a crucial role in regulating the activity, localization, and stability of proteins, and are essential for various cellular processes such as signaling, gene expression, and protein degradation. Studying protein modifications is important for understanding how proteins function in healthy cells and how their dysregulation can contribute to disease. This area of research is known as post-translational modification (PTM) and is a key focus in the fields of molecular biology, biochemistry, and cell biology.