Post-translational modification (PTM) refers to the chemical changes that occur to a protein after it has been synthesized by the ribosome. These modifications can include the addition of functional groups, such as phosphate or carbohydrate molecules, which can alter the protein's function, stability, or location within the cell. PTMs play a crucial role in regulating various biological processes, including cell signaling, metabolism, and gene expression. Common types of post-translational modifications include phosphorylation, glycosylation, and ubiquitination. Each of these modifications can significantly impact how proteins interact with other molecules and perform their roles in the cell. Understanding PTMs is essential for studying diseases and developing targeted therapies, as many diseases are linked to abnormal protein modifications.