Advanced Placement (AP) Biology Practice Exam

What occurs as a result of the binding of a signal molecule to a receptor?

1. The receptor is destroyed

2. The signal is amplified and translated

3. The ligand is released from the receptor

4. The signal is transported to the nucleus

The correct answer is: The signal is amplified and translated

The binding of a signal molecule, known as a ligand, to a receptor initiates a series of cellular events that often leads to the amplification and translation of that signal. When a ligand attaches to its specific receptor, it causes a conformational change in the receptor. This change activates the receptor and sets off a cascade of biochemical reactions within the cell, commonly referred to as a signaling pathway. This process often involves the activation of secondary messenger molecules, which can amplify the signal and propagate it throughout the cell. For instance, a single ligand-receptor binding event can result in the activation of multiple signaling molecules, leading to a considerable cellular response even when only a small amount of ligand is present. This mechanism is crucial for cells to respond efficiently to external signals, allowing for a wide range of physiological responses. In contrast, the other options do not accurately reflect the typical outcomes of ligand-receptor interactions. The receptor is not destroyed from the binding; instead, it usually remains intact after initiating the signal. The ligand remains bound for a period to instigate the signaling process rather than being released immediately. Finally, while signaling pathways can lead to changes in gene expression in the nucleus, the direct transport of the signal itself to the nucleus is not the first response observed