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Receptors Bind Specific Ligands

Receptors Bind Specific Ligands. Signal Transduction. Common ligands for receptors include ….. hormones – alter target cell metabolic behavior neurotransmitters – lead to action potential of neuron. synapse. nt receptors. dendrites. axon. myelin sheath. Cell body. nerve endings

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Receptors Bind Specific Ligands

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  1. Receptors Bind Specific Ligands Signal Transduction Common ligands for receptors include ….. hormones – alter target cell metabolic behavior neurotransmitters – lead to action potential of neuron

  2. synapse nt receptors dendrites axon myelin sheath Cell body nerve endings nt release Neuron schematic

  3. Membranes are electrically polarized

  4. Ion Channels in Nerve Signaling

  5. Molecular Components of Nerve Transmission Acetylcholine: neurotransmitter Acetylcholine Receptor Na+ voltage-gated channel K+ channel – (efflux) choline acetyltransferse : enzyme Acetylcholine Esterase : enzyme Na+/K+ ATPase (Pump) : Transporter

  6. Synapse (50nm): ACh diffusion Along Cell : depolarisation very rapid Signal Transmission in Nerve Cells

  7. Na+ ACh A + Ch Na+ Synapse Area Na+ ACh

  8. Nerve Transmission Chronology Nerve cell depolarised (stimulus) Releases ACh into next synapse 10nM  300 mM in 1ms ACh binds AChRa2bgd Na+ channel opens - depolarisation. opens voltage gated Na+ channels & action potential Na+/K+ pump removes Na+ ACh-esterase destroys ACh

  9. The Acetylcholine Receptor • Nicotinic acetylcholine receptor: • Ion channel for influx of Na+, Ca2+ • Gate opened by acetylcholine

  10. AChR

  11. AChR a2bgd 268,000 MW

  12. acetylcholine O + || (CH3)3 – N - CH2 - CH2 – O – C – CH3

  13. S S ACh L L L S L L S S ACh L S L ACh S L S S L S L ACh open form closed form

  14. ACh binding to AChR Ka = 108 M-1s-1 binding time = 100 ms closed  open = 30 ms stays open ~ 1ms impulse rate ~ 1000 s-1 Acetylcholine Esterase kcat = 25,000 s-1 KM = 12.5 mM kcat/KM = 2 x 108 M-1s-1

  15. O || CH3-C-O-CH2-CH2-N-(CH3)3 + Acetylcholine esterase Acetylcholine O || CH3-C-O- + HO-CH2-CH2-N-(CH3)3 +

  16. ACh binding to AChR • Blocked by snake venom proteins • Curare has same effect • Antibodies in Myasthenia Gravis • Result is Paralysis • Tetrodotoxin blocks Na+ channel

  17. Bungarotoxin (a snake venom) Binding to segment of AChR (red)

  18. Acetylcholine Esterase Inhibitors Parathion: insecticide Sarin: Nerve Gas As Alzheimer’s Medication Huperazine A: plant alkaloid & Chinese folk medicine Aricept (Donepezil)

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