Post-Translational Modification: Videos & Practice Problems

Post-translational modifications (PTMs) are covalent alterations that occur to proteins after they have been synthesized through translation. These modifications are crucial because they regulate protein activity, stability, interactions, and localization within the cell. PTMs can influence how proteins function and interact with other cellular components, thereby playing a significant role in various cellular processes. Common types of PTMs include methylation, acetylation, ubiquitination, and phosphorylation. Understanding PTMs is essential for comprehending how proteins achieve their final functional forms and how they contribute to cellular physiology and pathology.

Methylation and acetylation are both types of post-translational modifications, but they involve the addition of different chemical groups to proteins. Methylation is the addition of a methyl group (CH₃) to amino acids in a protein, often affecting gene expression and protein interactions. Acetylation, on the other hand, involves the addition of an acetyl group (COCH₃) to lysine residues in proteins, which can influence protein stability, localization, and interactions. Both modifications play critical roles in regulating protein function and cellular processes.

Ubiquitination is a post-translational modification where a ubiquitin protein is covalently attached to a target protein. This process often tags the protein for degradation by the proteasome, a protein complex responsible for breaking down unneeded or damaged proteins. Ubiquitination can also regulate protein activity, localization, and interactions. By controlling protein degradation and function, ubiquitination plays a vital role in maintaining cellular homeostasis and regulating various cellular processes, including cell cycle, DNA repair, and signal transduction.

Phosphorylation is a post-translational modification that involves the addition of a phosphate group (PO₄^3-) to specific amino acids, such as serine, threonine, or tyrosine, in a protein. This modification is catalyzed by enzymes called kinases. Phosphorylation can alter a protein's function, activity, interactions, and localization. It is a reversible process, with phosphatases removing the phosphate group. Phosphorylation is crucial for regulating various cellular processes, including signal transduction, cell cycle progression, and metabolic pathways.

Common types of post-translational modifications (PTMs) include methylation (addition of a methyl group), acetylation (addition of an acetyl group), ubiquitination (addition of ubiquitin), and phosphorylation (addition of a phosphate group). Other significant PTMs include hydroxylation (addition of a hydroxyl group), lipidation (addition of a lipid), glycosylation (addition of a carbohydrate), and sulfonation (addition of a sulfur group). These modifications regulate protein activity, stability, interactions, and localization, playing essential roles in various cellular processes.