Second messengers

Definition

Second messengers are small, intracellular molecules that relay signals received by cell surface receptors to target molecules inside the cell, thus amplifying and facilitating the cellular response to external stimuli. They play a critical role in various physiological processes by translating hormonal signals into specific cellular actions, often affecting metabolism and growth.

5 Must Know Facts For Your Next Test

1. Second messengers are key in amplifying the effects of hormones by enabling cells to respond rapidly to external signals with minimal energy input.
2. Common examples of second messengers include cAMP, inositol trisphosphate (IP3), and diacylglycerol (DAG), each serving distinct signaling roles.
3. The action of second messengers is typically short-lived, allowing for rapid changes in cellular activity in response to fluctuating hormone levels.
4. Second messengers can activate protein kinases that then modify target proteins through phosphorylation, ultimately leading to diverse physiological responses.
5. These messengers are crucial in regulating metabolic pathways such as glycogen breakdown, lipid metabolism, and cellular growth processes.

Review Questions

• How do second messengers amplify the effects of hormones on target cells?
  • Second messengers amplify hormonal signals by acting as intermediaries that transmit the signal from cell surface receptors to internal target molecules. When a hormone binds to its receptor on the cell membrane, it activates an enzyme that produces a second messenger, which then propagates the signal within the cell. This process allows a single hormone molecule to elicit a large-scale response, affecting multiple cellular activities simultaneously.
• Discuss the role of cAMP as a second messenger and its impact on metabolic processes.
  • Cyclic adenosine monophosphate (cAMP) is a key second messenger that mediates the action of several hormones, such as epinephrine and glucagon. Upon hormone binding, cAMP levels increase within the cell, activating protein kinase A (PKA), which then phosphorylates target proteins involved in metabolic pathways. This results in enhanced glycogen breakdown and increased glucose release into the bloodstream, demonstrating cAMP's crucial role in regulating energy metabolism.
• Evaluate how calcium ions function as second messengers in relation to hormone signaling and physiological responses.
  • Calcium ions act as versatile second messengers that are integral to various signaling pathways triggered by hormones. When certain hormones bind to their receptors, they can lead to an influx of calcium ions into the cytoplasm or release from intracellular stores. This increase in calcium levels activates several downstream processes such as muscle contraction, neurotransmitter release, and secretion of other hormones. The ability of calcium ions to influence multiple cellular functions highlights their importance in translating hormonal signals into physiological responses.

Related terms

cAMP: Cyclic adenosine monophosphate (cAMP) is a well-known second messenger that transmits signals from hormones like epinephrine and glucagon, triggering various metabolic responses.

calcium ions: Calcium ions serve as another crucial second messenger involved in various signaling pathways, affecting processes such as muscle contraction, neurotransmitter release, and hormone secretion.

protein kinase: Protein kinases are enzymes activated by second messengers that add phosphate groups to specific proteins, leading to changes in activity and function within the cell.