AEMCA Practice Exam

What does the second messenger system refer to in hormone action?

1. Direct interaction with DNA.

2. Attachment of amino acid hormones to cell membranes.

3. Release of glucose from the liver.

4. Insulin binding directly to receptor cells.

The correct answer is: Attachment of amino acid hormones to cell membranes.

The second messenger system refers to a mechanism by which certain hormones, particularly water-soluble hormones like amino acid-based hormones, exert their effects on target cells. In this system, hormones bind to specific receptors on the surface of the cell membrane. This binding triggers a cascade of internal cellular processes through the activation of second messenger molecules, such as cyclic AMP (cAMP) or calcium ions, which ultimately lead to a physiological response within the cell. Choosing the option about the attachment of amino acid hormones to cell membranes is correct because it highlights the fundamental aspect of how these hormones communicate with target cells through membrane receptors. Once the hormone attaches to its receptor on the cell surface, it doesn't enter the cell but initiates a series of reactions inside that lead to the desired cellular response. The remaining options describe mechanisms that do not accurately represent the second messenger system. Direct interaction with DNA pertains to lipid-soluble hormones, which can cross the membrane and affect gene expression directly, while insulin binding directly to receptor cells is more about insulin’s action that does not primarily engage the second messenger pathway. The release of glucose from the liver is a result of hormone action, but it's not a part of explaining the second messenger concept itself.