Which of the following represents the best order of signal transduction for the β-adrenergic receptor?

• A. Hormone → receptor tyrosine kinase → G-protein → protein kinase A → cAMP → cellular effects.
• B. Ligand → receptor → secondary messenger → G-protein → protein kinase A → cellular effects.
• C. Hormone → G-protein → receptor → cAMP → protein kinase A → cellular effects.
• D. Hormone → receptor → G-protein → second messenger → protein kinase A → cellular effects.

Answer: (D)

Verified step by step guidance

1. Understand the role of the β-adrenergic receptor in signal transduction, which is a process that converts a signal from outside the cell into a functional change within the cell.
2. Identify the components involved in the signal transduction pathway: the hormone (ligand), the receptor, the G-protein, the second messenger (such as cAMP), and protein kinase A.
3. Recognize that the β-adrenergic receptor is a type of G-protein-coupled receptor (GPCR), which means it interacts with G-proteins to transmit signals inside the cell.
4. Determine the correct sequence of events: the hormone binds to the receptor, activating the G-protein. The activated G-protein then stimulates the production of a second messenger, which in turn activates protein kinase A.
5. Conclude that the correct order of signal transduction for the β-adrenergic receptor is: Hormone → receptor → G-protein → second messenger → protein kinase A → cellular effects.