Advanced Placement (AP) Biology Practice Exam

What characteristic is associated with g-linked protein receptors?

1. Five alpha helices

2. Consists of seven alpha helices

3. Only functions in the nucleus

4. Interacts exclusively with DNA

The correct answer is: Consists of seven alpha helices

G-protein coupled receptors (GPCRs) are distinguished by their structure of seven alpha helices. This unique configuration allows them to span the cell membrane multiple times, which is essential for their role as receptors. When a ligand such as a hormone or neurotransmitter binds to the extracellular portion of a GPCR, it triggers a conformational change in the receptor. This change enables the receptor to interact with intracellular G-proteins, which then relay signals to various cellular pathways, leading to a physiological response. The seven alpha helices create a binding pocket that can specifically recognize a variety of signaling molecules, highlighting the versatility and importance of GPCRs in numerous biological processes, including vision, taste, odor detection, and immune responses. Their presence in the plasma membrane and ability to transmit signals across the membrane are crucial for cell communication. The other options do not accurately represent the structural characteristics or functional scope of GPCRs. For instance, five alpha helices would not provide the same functional mechanisms as seven. GPCRs do not function exclusively in the nucleus or interact with DNA; instead, they primarily act at the cell membrane and initiate intracellular signaling cascades.