Signaling Across Biomembranes

Signaling Across Biomembranes

• Signals from cells are mostly chemicals released into the extracellular fluid
• Signals can be transported to distant targets (endocrine), adjacent cells (paracrine), or the same cell (autocrine)
• Signaling conveys information to target cells, influencing processes like metabolism, gene expression, cell division, and differentiation
• Cell signaling has three stages: reception, transduction, and response
  • Reception: A cell recognizes a signal molecule (ligand) by a specific protein (receptor) on its surface or within the cytosol or nucleus
  • Transduction: The binding of ligand to receptor initiates a cascade of events that amplify or integrate the signal
  • Response: The final step in signal transduction that produces a cellular response, such as contraction, secretion, or metabolic reaction.
• Membrane receptors bind ligands outside the cell without crossing the plasma membrane. These include ligand-gated ion channels, G protein-coupled receptors, and enzyme-linked receptors.
• Ligand-gated ion channels allow ions to cross the membrane in response to ligand binding, rapidly changing cellular response.
• G protein-coupled receptors (GPCRs) are a large receptor family that use G-proteins to transmit signals inside the cell.
• Enzyme-linked receptors transmit signals through intracellular enzymes, like receptor tyrosine kinases (RTKs). These are involved in many cell growth and development processes.
• Receptor proteins can be categorized by their structure and methods of signaling.
• Phosphorylation/dephosphorylation regulate proteins involved in signal transduction.

Drug Modulation of Cell Signaling

• Drugs can modulate cell signaling through various mechanisms, including acting on receptors, enzymes, or ion channels.
• Drugs can act outside the cell membrane, on cell surface receptors, and on intracellular receptors.
• Drugs can modulate diverse cellular functions by binding in place of ligands, altering ion flow in ion channels, affecting intracellular second messengers, inhibiting/activating downstream signaling pathways, or directly regulating the receptor expression.
• Drugs can bind to receptors:
  • As agonists (mimicking natural ligands), triggering a cellular response
  • As antagonists (blocking natural ligands), preventing a cellular response
  • Drugs can also be inverse agonists (reverse the signaling).
• A graded dose-response curve plots the relationship between drug concentration and response.
• Drugs can be categorized as competitive reversible or competitive irreversible antagonists based on their binding.
• Drugs can also be non-competitive or allosteric antagonists that bind to a different site on the receptor.
• Important considerations about drug affinity and potency in targeting biological pathways are required.

Explore the intricate process of cell signaling, which involves the interaction of signals and receptors to influence cellular functions. This quiz covers the three stages of cell signaling: reception, transduction, and response, along with types of signaling pathways. Understand how these processes affect metabolism, gene expression, and more.