HISTOLOGY-Lecture 1-Movement Across Membranes

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lfield5
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HISTOLOGY-Lecture 1-Movement Across Membranes
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2011-01-29 15:34:17
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HISTOLOGY
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Lecture 1-Movement Across Membranes
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  1. Movement Across Membranes (types)
    • passive transport
    • simple diffusion
    • channel diffusion - ion channel proteins

    • active transport
    • ATP - carrier proteins
  2. Passive Transport
    NO USE OF ATP

    • simple diffusion
    • movement of particles from an area of high [ ]
    • to an area of low [ ]

    • channel diffusion
    • diffusion through aqueous channel proteins
    • carrier-mediated (uniport)
    • ion channel-mediated

    facilitated diffusion
  3. Simple Diffusion
    • movement of particles from an area of high [ ] to an area of low [ ] w/o ATP
    • non-polar molecules-
    • benzene
    • oxygen
    • nitrogen

    • uncharged-polar molecules-
    • H2O
    • glycerol

    • Factors
    • (1) [ ] gradient
    • (2) size of molecule involved
    • (3) distance the molecule has to travel
    • (4) temperature
    • (5) solubility of the molecule in lipid
    • (6) surface area of the membrane over which the molecule can work
  4. Channel Diffusion
    diffusion through aqueous channel proteins-can be regulated

    • particles involved-
    • ions
    • charged
    • particles
  5. Facilitated Diffusion
    • movement of ions & small molecules across a
    • membrane with the aid of transport proteins w/o ATP only in the direction of the [ ]

    • types-
    • (1) carrier-mediated – uniport
    • (2) ion channel mediated
  6. Active Transport
    movement of ions & small molecules from an area of low [ ] to an area of high [ ] using ATP

    requires – carrier proteins
  7. Ion Channel Proteins
    hydrophilic channels

    > 100 types

    • -specific – to one ion
    • -non-specific – 2(+) ions

    • ungated – always open
    • gated – regulate passage
    • aquaporins
  8. Ungated Ion Channel
    channel that is always open - ions/molecules follow diffusion gradient

    • ex.
    • K+ leak channel
    • sets up the resting membrane potential in neurons
  9. Gated Ion Channel
    regulate passage

    • Gross structure
    • a) channel domain
    • b) outer vestibule
    • c) selectivity filter
    • d) phosphorylation site
    • e) cell membrane

    • Molecular structure
    • a) typically four folded proteins
    • b) peripheral hydrophobic amino acids interact with hydrophobic acyl tails
    • c) hydrophilic amino acids face inward


    • Voltage-gated channels
    • Mechanically gated channels
    • Ligand-gated G-protein mediated
    • Ligand-gated intracellular phosphorylation mediated
  10. Voltage-Gated Ion Channel
    controlled by voltage - involved in action potentials

    • velocity-dependent
    • (1) fast channels
    • (2) slow channels

    • ex.
    • - Na+ channels
    • -Ca++ channels
  11. Mechanically Gated Ion Channel
    controlledby physical action

    • ex:
    • -movement of cilia - ear
    • -vibration
    • -pressure
  12. Ligand-Gated Ion Channel
    controlled by signal molecule (ligand) – gate remains open until ligand dissociates

    • types-
    • (1) extracellular
    • -ligand only
    • -ligand + G-protein
    • (2) intracellular

    • Ex:
    • - neurotransmitters
    • - hormones
    • - calcium ions
    • - hydrogen ions
  13. Ligand-Gated G-Protein Mediated Ion Channel
    controlled by signal molecule (ligand) – gate remains open until ligand dissociates

    • (1) chemical messenger attaches to cell membrane protein
    • (2) G protein activated
    • (3) activated nucleotide (2nd messenger) reacts with channel gate
    • (4) gate opens/closes

    • Ex:
    • -cardiac muscle cell
    • -vision (cGMP)
    • -smell (cAMP)
  14. Ligand-gated Intracellular Phosphorylation Mediated Ion Channel
    intracellular channel mediated by phosphate
  15. Aquaporins
    water channels impermeable to charged species (protons) preventing passage of ions/solutes

    12 types

    • a) allows flow of water into/out of cell
    • - water goes through single file- starts face-up – exits face-down

    • b) transports small uncharged solutes – pore size
    • (1) glycerol
    • (2) carbon dioxide
    • (3) ammonia
    • (4) urea
  16. Diseases & Disorders
    (relating to membrane transport)
    • ex:
    • Tetrodotoxin
    • Saxitoxin
    • Conotoxin
    • Lidocain/novcanine
    • Cystic fibrosis
    • Long QT syndrome
    • Brugada syndrome
  17. Brugada Syndrome
    blocks voltage-gated Na+ channels

    -genetic
  18. Long QT syndrome
    affects K+ channels

    -genetic
  19. Cystic Fibrosis
    • blocks Cl- channels
    • -genetic
  20. Lidocain & Novcanine
    blocks sodium channels

    -pain not transmitted
  21. Conotoxin
    – cone shells – various components

    • blocks
    • (a) voltage dependent Na+ channels
    • (b) voltage dependent Ca++ channels
    • (c) K+ channels
  22. Saxitoxin
    – dinoflagellate – red tides

    blocks voltage dependent Na+ channels
  23. tetrodotoxin
    – Puffer Fish

    blocks voltage dependent Na+ channels
  24. Carrier Proteins
    • multipass carrier proteins - can be active or passive
    • 1) solute binds to binding site
    • 2) reversible conformational change
    • 3) releases solute on other side
    • 4) returns to original conformation

    • primary active transport (Na+/K+ pump
    • secondary active transport (Co-transport)

    • carrying capacity
    • -uniport – one at a time
    • -coupled – two at a time
    • 1) symport – both in same direction
    • 2) antiport – opposite direction

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