Cell Signalling
Cell signalling is the fundamental process of communication among cells in multicellular organisms, crucial for regulating tissue development, cell growth, division, and overall function. This process often involves membrane trafficking, the continuous movement and recycling of cell membranes.
Key Mechanisms:
- Receptors on cell surfaces recognise extracellular molecular signals (ligands).
- Hydrophilic ligands bind to transmembrane receptors, initiating signal transduction via intracellular intermediaries. This often involves second messenger molecules (e.g., cAMP, DAG, IP3) that amplify the signal and lead to changes in gene expression or cell behaviour.
- Hydrophobic signalling molecules (e.g., steroids) diffuse through the plasma membrane and bind to intracellular receptor proteins, often moving to the nucleus to regulate gene transcription.
- Communicating junctions (gap junctions) allow direct exchange of ions and small molecules between adjacent cells for coordinated action.
Types of Signalling Routes: Signals reach target cells via various pathways:
- Endocrine signalling: Hormones travel through the blood to distant target cells.
- Paracrine signalling: Local chemical mediators act on nearby cells.
- Synaptic signalling: Neurotransmitters act on adjacent cells at specialized synapses.
- Autocrine signalling: Cells respond to their own secreted signals or signals from cells of the same type.
- Juxtacrine signalling: Signalling molecules on a cell surface or in the extracellular matrix bind to receptors on a directly contacting target cell.