Cell communication

• Types of stimuli cells can respond to

  • Growth factors
  • Death signals
  • Cell-cell contact
  • Cell-extracellular matrix contact
  • Hormones
  • Light (photons)
  • Odorants
  • Touch (mechanical stimulus)
  • Temperature
  • Oxygen levels
  • pH
  • Magnetic fields
  • Estrogen
• Cells can communicate over a range of distances through a variety of mechanisms
• Receptor protein


  Usually located in the plasma membrane and activated by a specific signaling molecule (ligand)
• Signal transduction


  1. Reception

  2. Activation

  3. Transmitting signal

  4. Cellular response
• Different types of receptor

  • Ligand-gated ion channels
  • G-protein coupled receptor (GPCR)
  • Enzyme linked receptors (receptor tyrosine kinases)
• Receptor activation


  Induces a conformation change that activates enzymes to relay the signal into the cell
• Enzyme-linked receptors


  Become activated following ligand binding and dimerisation
• The enzyme activity on one receptor molecule helps to phosphorylate and activate the other receptor molecule in the dimer
• This change in the receptor acts as a signal for other enzymes to be recruited to the receptor
• Signal amplification via second messengers allows a weak signal to be amplified so that the cell can respond rapidly
• Kinases


  A class of enzymes that attach phosphate groups to a target protein
• Phosphorylation


  Changes the protein structure leading to a change in activity i.e. it acts as an on/off switch
• Phosphatases


  A class of enzymes that reverse phosphorylation by removing the phosphate group
• Protein phosphorylation


  An example of a post-translational modification
• The addition of negative charges from the phosphate group to a protein can have significant effects on protein structure, leading to a conformational change
• Phosphorylation typically occurs on serine, threonine or tyrosine amino acids
• Humans have around 400 olfactory receptors
• Olfactory receptors bind to volatile odour molecules
• Individual odorant molecules can bind to many different receptors, but with different affinities
• Smells are made up of a number of odorant molecules triggering a pattern of receptor activation which is then interpreted by the brain
• Molecular recognition


  Recognition of ligand by the receptor, recognition of targets by kinases
• Molecular switches


  Phosphorylation/dephosphorylation by kinases/phosphatases, G-proteins
• Signal amplification


  Second messenger production, enzyme activity
• Cells are constantly being bombarded with multiple signals
• Sometimes these signals can send conflicting messages
• Cells need to process the information they receive and then make the correct response