AN SC 310 - 2

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AN SC 310 - 2
2012-09-19 22:44:41
AN SC 310

Lecture 2 - Communication Between Cells
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  1. What are the 2 mechanisms of intercellular communication?
    • 1. Direct Communication through Gap Junctions
    • 2. Indirect Communication through Chemical Messengers
  2. Describe Gap Junctions
    • Channels formed between 2 cells
    • - Protein channels made of connexin
    • - 6 connexins = 1 connexon
    • Allow flow of ions
    • Direct electrical and metabolic coupling
    • Common in smooth and cardiac muscles
  3. What are the functional classifications of chemical messengers?
    • Paracrines
    • Autocrines
    • Neurotransmitters
    • Hormones
    • Neurohormones
    • Cytokines
  4. Describe Paracrines
    Released by cell, moves to target cell by diffusion, act on neighboring cells

  5. Give an example of a Paracrine

    Released with tissue damage and causes dilation of local blood vessels
  6. Describe Autocrines
    Subclass of Paracrines

    Act on same cell that releases it/source and target are the same

  7. Describe Neurotransmitters
    Messenger of the nervous system; released into the ECF of synaptic cleft from neurons, diffuses to very close target cell

    Also called Synaptic Transmission

  8. Describe Hormones
    Messenger of endocrine system; released from endocrine cells into blood, transported in blood to target cell (cell with specific receptor)

    Examples: Insulin, estrogen, thyroxin

  9. Describe Neurohormones
    Special class of hormone; produced by neurons, secreted into blood via ISF, transported to target cell

    Examples: ADH, oxytocin

  10. What are the solubility classifications of messengers?
    • Lipophobic (hydrophilic)
    • Lipophilic (hydrophobic)
  11. Describe Lipophobic Ligands
    • Not lipid soluble (is water soluble)
    • Does not easily cross cell membrane, may require pumps/channels
    • Receptors on cell membrane
    • General action of target response is enzyme activation, and membrane permeability changes
  12. Describe Lipophilic Ligands
    • Lipid soluble (not water soluble)
    • Easily crosses cell membrane
    • Receptor location intracellular
    • General action of target response is via gene activation
  13. What are the chemical class classifications of messengers?
    • Amino Acids
    • Amines
    • Peptides & Proteins
    • Steriods
    • Eicosanoids
  14. Describe Amino Acid Messengers
    • Lipophobic
    • 4 AA are chemical messengers, all neurotransmitters
    • 1. Glutamate
    • 2. Aspartate
    • 3. Glycine
    • 4. GABA
  15. Describe Amine Messengers
    • Lipophobic (except thyroid hormones)
    • Derived from AA
    • Contains amine group (NH2)
  16. Give examples of amine messengers
    1. Catecholamines - derived from tyrosine, includes Dopamine, Norepinephrine, Epinephrine

    2. Thyroid Hormones - derived from two tyrosine AA

    3. Histamine - derived from histadine

    4. Serotonin - derived from tryptophan
  17. Describe Peptide & Protein Messengers
    • Most abundant ligand
    • Lipophobic
    • Made of chains of AA
    • Peptide ligand < 50 AA
    • Protein ligand > 50 AA
  18. Describe Steroid Ligands
    • Lipophilic
    • Derived from cholesterol
    • All function as hormones
  19. Describe Eicosanoid Ligands
    • Lipophilic
    • Derived from arachidonic acid (cell membrane phospholipid)
  20. What are the methods of synthesis and release in chemical messengers?
    • Lipophilic Messengers - Diffusion
    • - Released upon synthesis
    • - Cannot be stored, synthesized on demand

    • Lipophobic - Exocytosis
    • - Stored in vesicles prior to release
    • - Regulate rate of exocytosis
  21. Which functional classes are transported via diffusion?
    • Paracrines
    • Autocrines
    • Neurotransmitters
  22. Which functional classes are transported via blood?
    • Hormones
    • Neurohormones
  23. What affects a messenger's half life?
    Whether it is dissolved in the plasma or bound to a carrier protein.

    • Dissolved - short HL, ex. insulin (10 min)
    • Bound - long HL, ex. cortisol (90 min)
  24. Define Receptor
    Protein with specific binding sites for messengers
  25. What are properties of receptors?
    Specifity to messenger

    Often more than one type of receptor for one messenger

    One cell may have receptors for diff messengers or diff types of receptors for one messenger
  26. What affects the magnitude of response?
    • # of receptors with messengers bound to them
    • Concentration of messenger
    • # of receptors on target cell
    • Affinity of receptor for messenger
  27. Define Signal Transduction
    Process by which messenger binding to receptor produces response in target cell
  28. What does Signal Transduction depend on?
    Messenger and Receptor Types

    • Lipophilic messenger - Receptor inside cell
    • Lipophobic messenger - Receptor on plasma membrane
  29. Describe Lipophilic Messengers
    • Bind to receptor in cytoplasm or nucleus
    • If cytoplasm, rec/mes complex enters nucleus
    • Alters transcription
  30. Describe Lipophobic Messengers
    • Bind to membrane-bound receptors
    • Channel-linked Receptors
    • Enzyme-linked Receptors
    • G Protein-linked Receptors
    • "Cascade" of events
  31. Define Channel-linked Receptors
    Receptor that opens/closes ion channels in response to messenger binding

    • 1. Fast ligand-gated channels
    • 2. Slow ligand-gated channels
  32. What is the difference between fast and slow ligand-gated channels?
    Fast ligand-gated channels - receptor and channel are on the same protein

    Slow ligand-gated channels - receptor and channel are on seperate proteins, linked by G Protein, changes in transport of ians through channel causes target response
  33. Describe Enzyme-linked Receptors
    • One protein for receptor and enzyme
    • No channels

    Examples: Tyrosine kinase, Guanylate cyclase
  34. Describe G Protein-linked receptors
    • G Proteins are regulatory proteins
    • G Proteins link ECF messenger to ion channels or amplifier enzymes
  35. Define First Messenger
    Extracellular messenger
  36. Define Second Messenger
    Intracellular messenger
  37. How are second messengers produced? List the steps.
    • First messenger binds to receptor and activates G protein
    • G protein activates amplifier enzyme
    • Amplifier enzyme activates production of second messenger
  38. What are the 2 types of G Proteins?
    Gs - stimulatory; activates amplifier enzyme

    Gi - inhibitory; inhibits amplifier enzyme
  39. What is the purpose of the second messenger?
    Signal amplification
  40. List types of second messengers
    • Cyclic AMP - cAMP (most common)
    • Cyclic GMP - cGMP
    • Inositol triphosphate - IP3
    • Diacetylglucerol - DAG
    • Calcium ions