Phosphorylation __________.

• A. always inactivates a protein
• B. activates G-protein-coupled receptors
• C. is accomplished by protein phosphatases
• D. always activates a protein
• E. can either activate or inactivate a protein

Answer: (E)

Verified step by step guidance

1. Understand the concept of phosphorylation: Phosphorylation is a biochemical process that involves the addition of a phosphate group to a protein or other organic molecule. This process is crucial in regulating protein function and signaling pathways within cells.
2. Recognize the role of kinases: Protein kinases are enzymes that catalyze the transfer of phosphate groups from high-energy molecules like ATP to specific substrates, typically proteins. This process can alter the activity, interactions, or localization of the protein.
3. Consider the effects of phosphorylation: Phosphorylation can lead to either activation or inactivation of a protein. The effect depends on the specific protein and the site of phosphorylation. It can change the protein's shape, charge, or ability to interact with other molecules.
4. Differentiate between phosphorylation and dephosphorylation: While phosphorylation involves adding a phosphate group, dephosphorylation is the removal of a phosphate group, typically accomplished by enzymes called phosphatases. This process can reverse the effects of phosphorylation.
5. Apply this understanding to the problem: Given the options, recognize that phosphorylation does not always activate or inactivate a protein. It can have either effect depending on the context, which aligns with the correct answer provided.