Advanced Placement (AP) Biology Practice Exam

What role does a protein kinase play in signal transduction?

1. It removes phosphate groups from proteins

2. It transfers phosphate groups from ATP to proteins

3. It allows ions to flow into the cell

4. It relays signals to a cell's interior

The correct answer is: It transfers phosphate groups from ATP to proteins

In signal transduction, protein kinases play a crucial role by transferring phosphate groups from ATP to specific target proteins. This phosphorylation process can result in a conformational change in the protein, altering its activity, function, or interaction with other molecules. This modification is essential in signaling pathways, as it can activate or deactivate enzymes, facilitate protein-protein interactions, or modify cellular functions. The addition of phosphate groups often acts as a switch, allowing cells to respond to external signals such as hormones or growth factors. The action of protein kinases is integral to the amplification of signals within the cell, as one kinase can activate multiple downstream targets, leading to a coordinated cellular response. This mechanism highlights the importance of protein kinases in regulating cellular processes and maintaining homeostasis.