The Biology Project > Cell Biology > Cell Signaling > Overview

Essential Concepts Cell Signaling

  1. All cells are equipped with elaborate systems for receiving signals from their environment. The mechanisms involved in cell signaling are particularly crucial for understanding multi-cellular organisms, and are an important in many diseases. Signaling systems are providing new targets for treating disease.
  2. Cells receive signals from their environment (light, odor, sound, nutrients) and other cells (divide, differentiate, migrate, transmit signals).
  3. Signaling involves a receptor, the transduction of information from the cell surface to inside the cell, and subcellular systems that make a response.
  4. Receptors are proteins with specific binding sites for signaling molecules called ligands. Membrane soluble ligands include steroid hormones (estrogen) which bind to cytoplasmic receptors. Most other signaling molecules (peptides, proteins, gases, ions, nucleotides) bind to integral membrane proteins.
  5. Types of receptors include ion channels that can open or close (gated) allowing ions to enter or leave cells, enzyme linked that activate endogenous or exogenous protein kinases (phosphate transferring enzymes), and serpentine or G-protein-linked.
  6. Ligand binding to receptor results in the production of second messengers (cAMP, cGMP, IP3, Ca++, DAG, NO). Activation frequently involves protein kinase cascades, a series of amplification steps resulting in a rapid response.
  7. Cells can have similar receptors, but make very different responses to the same ligand. The response made depends on the availability of targets. One cell may have target proteins that leads to altered transcription, while another has target proteins that leads to cell differentiation or division.
  8. Animal and plant cells have membrane proteins that permit direct cell to cell communication by opening channels between cell cytoplasms. These are called gap junctions in animal cells and plasmodesmata in plant cells.

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