Post Translational Modification: Videos & Practice Problems

Cells regulate their biochemical reactions through various mechanisms, one of which is post-translational modifications (PTMs). These modifications occur after the translation process, where proteins are synthesized from mRNA. The term "post" indicates that these changes happen following the initial protein formation. PTMs are crucial as they involve covalent alterations that specifically control protein activity, influencing their function and stability.

There are numerous types of PTMs, with several hundred identified, but some of the most common ones include methylation, acetylation, ubiquitination, phosphorylation, hydroxylation, lipidation, disulfide bond formation, sulfonation, and glycosylation. Each of these modifications plays a distinct role in protein functionality:

• Hydroxylation: This process involves the addition of a hydroxyl group (-OH) to a protein, which can affect its structure and function.
• Methylation: In this modification, a methyl group (-CH₃) is added to the protein, influencing gene expression and protein interactions.
• Lipidation: This involves the attachment of lipid molecules to proteins, which can affect membrane localization and signaling.
• Acetylation: The addition of an acetyl group (-COCH₃) can regulate protein stability and interactions.
• Disulfide Bonds: These covalent bonds form between the sulfur atoms of cysteine residues, stabilizing protein structure by linking polypeptide chains.
• Ubiquitination: This modification involves the addition of ubiquitin, a small protein that tags other proteins for degradation or alters their activity.
• Sulfonation: The addition of a sulfate group (-SO₄) can modify protein function and interactions.
• Glycosylation: This process adds carbohydrate moieties to proteins, which can affect their stability, localization, and recognition by other molecules.
• Phosphorylation: The addition of a phosphate group (-PO₄) is a key regulatory mechanism that can activate or deactivate enzymes and signaling pathways.

Understanding these modifications is essential for grasping how proteins function within the cell and how their activities can be finely tuned in response to various signals. As the course progresses, a deeper exploration of specific PTMs will enhance comprehension of their roles in cellular processes.

Proteolytic cleavage is a crucial post-translational modification involving the breakdown of peptide bonds between amino acid residues in proteins. This process is facilitated by enzymes known as proteases or peptidases, which specifically cleave peptide bonds at designated amino acid sites. Following translation, some proteins exist in an inactive form and require proteolytic cleavage to become functional. This activation process can be visualized as the action of molecular scissors, where proteases cut the protein to convert it into its active form.

During proteolytic cleavage, the enzyme may also generate inactive fragments or remove non-functional portions of the protein. This selective cleavage is essential for the proper functioning of many proteins, as it can determine their activity and role within biological systems. Understanding proteolytic cleavage is particularly important when discussing zymogens, which are inactive precursors that require cleavage to become active enzymes. As the course progresses, further exploration of proteolytic cleavage and its implications will enhance comprehension of protein functionality and regulation.