Advanced Placement (AP) Biology Practice Exam

In the context of signal transduction, a G protein plays a crucial role by acting as a molecular switch that relays signals from a receptor to other proteins within the cell. When a signaling molecule, such as a hormone or neurotransmitter, binds to a cell surface receptor, it activates the G protein associated with that receptor. This activation often involves the exchange of GDP for GTP on the G protein.

Once activated, the G protein can interact with and influence a variety of downstream target proteins, such as enzymes or ion channels, thus propagating the signal throughout the cell and leading to a specific cellular response. This process is essential for many physiological functions and helps integrate and amplify the signals received by cells, making the G protein a central component in many signaling pathways.

The G protein's ability to relay signals effectively allows it to modulate a wide range of cellular activities, ranging from metabolic processes to growth and immune responses. The specificity and versatility of G proteins in these signaling pathways underline their importance in cellular communication.