Week 4

Week 4

1. Chemical Communication Between Cells

   • Alzheimer's
     • dementia - serious deterioration in mental functions
     • most common type
     • symptoms caused by nerve cells dying and connections degenerating
     • memory is normally the first thing to be lost
     • over 0.5 million with alzheimer's
     • no drug currently cures or halts it
     • there is a build up of amyloid
     • amyloid aggregates and sticks to proteins on the nerve cell surface
   • Why Communicate?
     • mechanisms needed to control timing and release during development
     • mechanisms needed to allow monitoring and response
   • Cell to Cell Communication
     • extracellular signals secreted and act on target cells
     • ligands act as signals and bind to receptors
     • contact dependant - membrane bound signal
     • paracrine - local mediator reacts with local cells
     • autocrine - signal binds to the same cell
     • synaptic - neurotransmitter carries on electrical impulse
     • endocrine - hormone released into blood stream
   • gap junctions
     • pores between cells
     • allow free movement of ions and small molecules
   • Ligands
     • amino acids - neurotransmitters
     • amines - catecholamines, serotonin, hystamine and thyroid hormones
     • peptides
     • steriods
     • eicosanoids
     • classification
       • intracellular receptors - lipophilic ligands diffuse across plasma membrane and bind to receptors in the cytosol or nucleus
       • cell surface receptors - lipophobic ligands bind to receptors on the cell surface
   • Mechanism of Lipophilic Ligands
     • signal diffuses into cell
     • signal diffuses into nucleus
     • signal binds to hormone reponse element
     • gene expression is altered
   • Cell Surface Receptors
     • enzyme-linked
       • receptor and enzyme linked to same protein
       • signal binds to receptor causing a conformational change and the enzyme is activated
     • ion channel-linked
       • ligand gated channels
       • receptor binding causes ion channels to be opened
     • G protein-coupled
       • link signal to an enzyme or channel
       • receptors coupled to G proteins which are activated on signal binding
   • Secondary Messengers
     • intracellular signalling molecules
     • produced upon binding of first messenger
     • signal amplification
     • needs something to stop it being produced e.g. cAMP or gAMP
   • Cytosolic Calcium and Signal Transduction
     • Ca conc in cell - 0.1-1 micromolar
     • extracellular conc of Ca - 1 millimolar
     • gradient across cell membrane and ER membrane
     • active transport across cell membrane
     • Ca ion channels voltage dependant, IP3 gated or ryanodine receptors
     • sequestration
     • active transport into organelles
     • changes membrane potential - muscle contraction and exocytosis
   • Diversity of Reponses
     • different cells react differntly to the same receptor
     • can be more than one receptor per ligand
     • cells are specialised to respond to similar signalling systems

2. Electrical Communication Between Cells

   • Nerves
     • an electrical potential exists across the plasma membrane called the resting potential
     • in neural and muscles cells the potential changes
     • electrical impulses pass along the cells due to the permeability of Na and K
     • resting potential
       • K flows out of the cell through open K channels
       • Na tries to flow into the cell
       • K flowing out of the cell causes a negative charge in the cell so they stop flowing out
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3. Intracellular Signalling