OCR A Level Biology

Revision Notes

5.1.3 Cell Signalling

Cell Signalling

  • Cell signalling is the process by which cells communicate with each other
  • Cell signalling is very important as it allows multicellular organisms to control and coordinate their bodies and to respond to their environments
  • Cell signalling pathways coordinate the activities of cells, both between cells that are very close to each other and between cells that are large distances apart within the organism
  • The basic stages of cell signalling are:
    • A stimulus is received by a receptor cell
    • The stimulus is converted to a signal (nearly always a chemical) that can be passed on – this process is known as transduction
    • The signal is transmitted to a target cell (effector) that can detect it (via receptors in its cell membrane)
    • An appropriate response is made

Basic stages of cell signalling pathway, downloadable AS & A Level Biology revision notes

The basic stages of a cell signalling pathway

  • In animals, cell signalling pathways can be categorised into two types, depending on how far the signal must travel:
    • Paracrine signalling (signalling between cells that are close together)
    • Endocrine signalling (signalling between cells that are far apart, which involves the signalling molecule being transported in the circulatory system)
  • The signalling molecules produced by cells can belong to various chemical groups, including proteins, glycoproteins, amino acids, lipids and phospholipids
    • In endocrine signalling, however, the signalling molecules are always hormones

Cell membranes

  • Transmission of messages in cell signalling pathways requires crossing barriers such as cell surface membranes
  • Cell surface membranes are therefore very important in signalling pathways as the membrane controls which molecules (including cell signalling molecules) can move between the internal and external environments of the cell
  • Signalling molecules are usually very small for easy transport across cell membranes
  • The receptor molecules on or in the cell surface membrane are proteins or glycoproteins
    • Some receptors, such as oestrogen receptors, may be present in the cytoplasm (in this case, because steroid hormones can diffuse through the cell membrane)
  • The signalling molecule binds to the receptor molecule, causing specific changes in the receiving cell

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