RECEPTORS

Super Families of Receptor Proteins
1. Plasma Membrane
  1. ligand gate ion channels
    1. eg nicotine and acetyl choline receptors
  2. G Protein coupled receptors
    1. aka signal proteins structure: 7 helices with N terminal on outside
    2. Binding site on inside usually closed, ligand binding causes conformational change to open this
    3. G protein (alpha beta & gamma) binds to inner bindng site
      1. Alpha usually has GDP (guanosine diphospate) which is then replaced GTP on activation
        Gamma and beta separate
        alpha inactivated when its own phosphoryating GTPase or protein phosphotase activity turn GDP to GTP
        G protein subunits recombine and attach to cell membrane
    4. alpha activates adenylate cyclase to produce cyclic AMP
      1. (secondary messenger) can go on to activate protein kinase A which activates phosphorylation of theorine and serine in other enzymes( glycogen to glucose)
    5. DRUGS
      1. Beta adrenergic receptors switched on by adrenaline
        B1 open calcium channels
        B2 close channels - asthma - relaxing smooth muscles
      2. Muscuranic receptors -cholinergic receptors on smooth muscles and cardiac tissue
        agonists switching on GI after surgery
        antagonists close GI after surgery
        shaking in parkisons
  3. tyrosine kinase receptors
  4. contain intra, extra & transcellular membrane
2. cytosolic intracellular
  1. nucleur hormone receptors
    1. involved in every major organ and metabolic system eg bone, muscle, hormone mediated cancer, homeostasis, sexual and embryonic development
    2. 2. binds receptor- conformational change
    3. 1. ligand crosses membrane
    4. 3. dimerisation
    5. 4. proteinsythesis
    6. 5. binds to coactivator protein
    7. 6. complex transloacates to nucleus and binds to specific region of DNA
      1. initiates transcription- directly involved in gene expression
    8. single protein steroid binding region near C terminal and DNA binding region near N terminal
      1. DNA binding region = zinc fingers 9 cysteine residues, 8 contain zinc to stabilise structure
        dimer- both need to be activated- identifies particular nucleuotide sequence
    9. for steroids and thryroid
    10. DRUGS
      1. Glucocorticoid receptor: using adrenal gland extracts (cortisone) for allergy treatment. Abused by athletes.
      2. Progesterone Receptor: control ovulation
      3. Oestrogen receptor: using oestradiol for fertility control and breast cancers
        oestrodiol = steroid effect growth and development
        H12 folds across binding site which then exposes Activation Function AF2 (hydrophobic) after step two
        Tamoxifen for breast cancer- prevents binding of oestrogen to its receptor
3. can be classified based on pharmacological activity (drug/ligand) nature here classified by structural pathway
Signal transduction process
1. Receptors = proteins receive endo/exodogenous signals
  1. including hormones, neurotransmitters, local chemical mediators eg prostaglandins
2. Bind with high affinity, causing conformational change
3. Chemical signal transferred to intra cellular message
Drugs & Receptors
1. ANTAGONIST
  1. competitive or non competitive
    1. binds to receptor but does not exert effect on cell
2. AGONIST
  1. partial or full
    1. exerts effect on cell

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RECEPTORS

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