Second messenger

Definition

A second messenger is a small, intracellular signaling molecule that transmits signals from receptors on the cell surface to target molecules inside the cell, leading to a physiological response. These messengers play a crucial role in amplifying and relaying the effects of extracellular signals, such as hormones or neurotransmitters, thereby facilitating communication within the cell and regulating various cellular processes.

5 Must Know Facts For Your Next Test

1. Second messengers can be produced rapidly in response to receptor activation, allowing for quick cellular responses to external signals.
2. Common second messengers include cyclic AMP (cAMP), inositol trisphosphate (IP3), and calcium ions, each with distinct roles in signaling pathways.
3. The action of second messengers often involves the activation of specific protein kinases, which then phosphorylate target proteins to modulate their activity.
4. Second messenger systems allow for signal amplification; a single ligand binding to a receptor can trigger the production of many second messenger molecules.
5. Dysregulation of second messenger signaling can lead to various diseases, including cancer, diabetes, and heart disease.

Review Questions

• How do second messengers amplify the signals received by cells from external stimuli?
  • Second messengers amplify signals by acting as intermediaries between cell surface receptors and intracellular targets. When a ligand binds to a receptor, it activates a cascade of reactions that can produce multiple second messenger molecules. For instance, one activated G protein-coupled receptor can generate many cAMP molecules, each of which can activate protein kinases. This amplification allows a small external signal to produce a significant cellular response.
• Discuss the roles of different types of second messengers in cellular signaling pathways and provide examples.
  • Different types of second messengers have specific roles in cellular signaling pathways. For example, cyclic AMP (cAMP) primarily activates protein kinase A (PKA), leading to various physiological responses like glycogen breakdown. In contrast, calcium ions serve multiple functions including muscle contraction and neurotransmitter release. Inositol trisphosphate (IP3) can trigger the release of calcium from the endoplasmic reticulum. These diverse functions demonstrate how second messengers coordinate complex cellular responses.
• Evaluate the implications of second messenger dysfunctions on human health and disease.
  • Dysfunctions in second messenger systems can have serious implications for human health and are linked to various diseases. For example, mutations in components of these signaling pathways may lead to uncontrolled cell growth, contributing to cancer development. Similarly, altered calcium signaling is associated with heart disease and neurodegenerative disorders. Understanding these pathways provides insight into potential therapeutic targets for treating such conditions.

Related terms

G protein-coupled receptors:

A large family of membrane receptors that transmit signals through the activation of G proteins, leading to the production of second messengers.

cAMP:

Cyclic adenosine monophosphate, a common second messenger involved in signal transduction pathways that regulate various physiological processes.

calcium ions: Inorganic ions that serve as important second messengers in many signaling pathways, playing key roles in muscle contraction, neurotransmitter release, and other cellular activities.