Which of the following functional groups is commonly involved in signal transduction in biological systems?

• A. Hydroxyl group ($O^{\mathrm{H}}$)
• B. Amine group (${\mathrm{NH}}_2$)
• C. Carbonyl group ($C=O$)
• D. Phosphate group (${\mathrm{PO}}_4-$)

Answer: (D)

Verified step by step guidance

1. Understand the context: Signal transduction is a process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly involving protein phosphorylation catalyzed by protein kinases.
2. Identify the role of functional groups: In biological systems, certain functional groups are key players in signal transduction due to their ability to undergo reversible modifications.
3. Focus on phosphorylation: The phosphate group is crucial in signal transduction because it can be added to proteins by kinases, altering the protein's function and activity.
4. Compare with other groups: Hydroxyl, amine, and carbonyl groups are important in various biochemical processes, but they are not primarily involved in the reversible phosphorylation events central to signal transduction.
5. Conclude the analysis: Recognize that the phosphate group is the functional group most commonly involved in signal transduction due to its role in phosphorylation and dephosphorylation cycles.