Why is the activation of a protein kinase an important step in signal transduction?

• A. Kinases bind to receptors and prevent binding of the ligand.
• B. Kinases prevent signal amplification by degrading specific enzymes in the cell.
• C. Kinases can activate or inactivate proteins by phosphorylation.
• D. Kinases are secreted by a cell as a signaling molecule.

Answer: (C)

Verified step by step guidance

1. Understand the role of protein kinases in signal transduction: Protein kinases are enzymes that modify other proteins by chemically adding phosphate groups to them (phosphorylation). This process can activate or inactivate the target proteins, thereby playing a crucial role in regulating cellular activities.
2. Recognize the importance of phosphorylation: Phosphorylation is a reversible post-translational modification that can alter the function, activity, location, or interaction of proteins. It is a key mechanism in signal transduction pathways, allowing cells to respond to external signals.
3. Identify the effect of phosphorylation on proteins: When a protein kinase phosphorylates a target protein, it can cause a conformational change in the protein structure. This change can either activate or deactivate the protein's function, depending on the specific protein and the context within the cell.
4. Consider the role of kinases in signal amplification: Protein kinases can amplify signals by activating multiple downstream proteins in a signaling cascade. This amplification is crucial for the cell to generate a significant response from a relatively small initial signal.
5. Differentiate between kinases and other signaling molecules: Unlike kinases, which modify proteins within the cell, some signaling molecules are secreted by cells to communicate with other cells. Kinases typically function within the cell to propagate and regulate signals through phosphorylation.