Advanced Placement (AP) Biology Practice Exam

What occurs to the structure of a receptor following ligand binding?

1. It degrades

2. It undergoes phosphorylation

3. It experiences a conformational change

4. It remains unchanged

The correct answer is: It experiences a conformational change

Upon ligand binding, a receptor experiences a conformational change, which is fundamental to its function in cellular signaling. Ligands, such as hormones or neurotransmitters, bind to specific receptors on the cell surface or within cells. This binding event triggers a change in the shape or structure of the receptor. This conformational change is critical because it often promotes the activation of downstream signaling pathways. For example, in G-protein coupled receptors (GPCRs), the alteration in the receptor's shape allows it to interact with G-proteins, which then can activate or inhibit various intracellular signaling pathways. Similarly, in enzyme-linked receptors such as receptor tyrosine kinases, ligand binding leads to dimerization and autophosphorylation, further propagating the signal within the cell. Overall, the structure of the receptor must change to enable these interactions, thereby allowing the cell to respond appropriately to external signals.