Signal Transduction Mechanisms

Signal Transduction Mechanisms

1. Signalling Cascade

   • Describes the series of biochemical reactions involved in signal transduction

2. Intracellular Signalling Molecules

   • Phosphoinositide Derivatives
     • PIP3, DAG, IP3
   • Calcium Ions
   • Cyclic Nucleotides
     • cAMP, cGMP

3. Ion Channeled Coupled Receptors

   • Recognise their ligand and opens a gap in the membrane
     • The gap in the membrane is known as the channel
       • ions can pass through the channel
         • The signal is relayed in the ions
   • Can also be opened by a potential across the membrane
   • Found in fast responding cells like muscle or nerves
   • Entry of + ions into the channel causes depolarisation and activates the target cell

4. Acetylcholine Nicotinic Receptors

   • Tubocurarine
     • competitive reversible antagonist of Acetylcholine at nicotinic receptors
     • used to relax skeletal muscle cells in surgery
     • actions reversed by increasing ACh concentration
       • This is done by inhibiting the enzyme which destroys ACh
     • nicotinic receptors found on skeletal muscle cells
   • GABA
     • Gamma Amino Butyric Acid
     • Opens a Cl- channel
       • hyperpolarisation and cell inhibition
     • drugs acting here are classified as tranquilizers/anticonvulsants

5. G Protein Coupled Receptors (GPCR's)

   • largest known protein family involved in many pathological pathways
     • So big 40-50% of drugs target GPRCs
   • integral membrane proteins that have 7 membrane spanning domains or transmembrane helices
     • extracellular parts of the helix can be glycosylated
       • Glycosylated: Sugars chemically attached to proteins to produce glycoproteins
   • Physiological roles
     • Sense of smell
     • Visual Sense
     • Regulation of behaviour
       • receptors in the brain bind different neurotransmitters
         • Serotonin and Dopainic
     • Reguation of immune system and inflammation
       • chemokine receptors
         • bind ligands that mediate intracellular communication between immune cells
     • Autonomic Nervous System Transmission
       • Both parasympathetic and sympathetic systems regulated by GPRC's
         • responsible for the control of many body functions like BP and HR