In the context of cell signaling, which of the following best describes the role of a ligand when it binds to a cell surface receptor?

• A. It directly synthesizes new proteins in the cytoplasm.
• B. It transports ions across the plasma membrane.
• C. It initiates a signal transduction pathway inside the cell.
• D. It degrades the receptor to terminate the signal.

Answer: (C)

Verified step by step guidance

1. Understand the concept of cell signaling: Cell signaling is the process by which cells communicate with each other using signaling molecules, such as ligands, to trigger specific responses.
2. Define the term 'ligand': A ligand is a molecule that binds specifically to a receptor on the cell surface or inside the cell, initiating a biological response.
3. Explain the role of a receptor: Receptors are proteins located on the cell surface or within the cell that recognize and bind to ligands. This binding triggers a signal transduction pathway, which is a series of molecular events leading to a cellular response.
4. Clarify the function of signal transduction: Signal transduction pathways amplify and relay the signal from the ligand-receptor interaction to produce a specific cellular response, such as gene expression, enzyme activation, or changes in ion concentrations.
5. Conclude the correct description: When a ligand binds to a cell surface receptor, it does not directly synthesize proteins, transport ions, or degrade the receptor. Instead, it initiates a signal transduction pathway inside the cell, leading to the desired cellular response.