Advanced Placement (AP) Biology Practice Exam

What is the function of adenylyl cyclase in cell signaling?

1. It binds to DNA and activates transcription

2. It converts ATP to cyclic AMP

3. It amplifies the signal at the cell membrane

4. It initiates the reception stage

The correct answer is: It converts ATP to cyclic AMP

Adenylyl cyclase plays a crucial role in cell signaling by catalyzing the conversion of ATP (adenosine triphosphate) into cyclic AMP (cAMP), a secondary messenger in various signaling pathways. When a signaling molecule, such as a hormone or neurotransmitter, binds to a receptor on the cell membrane, it can activate adenylyl cyclase through G-proteins. This enzymatic conversion of ATP to cAMP is significant because cAMP acts as a secondary messenger that relays the signal within the cell, activating downstream signaling pathways, which can lead to various cellular responses. The generation of cAMP by adenylyl cyclase amplifies the original signal initiated by the receptor-ligand binding. This amplification is critical for ensuring that even a small amount of signaling molecule can invoke a substantial cellular response. Therefore, the function of adenylyl cyclase is essential for the effective transmission of signals inside the cell following external stimuli.