Week 4

Week 4

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

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