Download membrane potential

TRANSPORT ACROSS
MEMBRANES, MEMBRANE
POTENTIAL, OSMOSIS
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SIGNIFICANCE OF TRANSPORT ACROSS
MEMBRANES IN MEDICINE
Example:
• Membrane transporter: CFTR (cystic fibrosis transmembrane
regulator)
• Disease: cystic fibrosis
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TRANSPORT ACROSS MEMBRANES,
MEMBRANE POTENTIAL, OSMOSIS
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Basic types of membrane transport
Diffusion of substances across membrane
Passive vs. active transport mediated by transport proteins
Types of transport proteins
Transport mediated by carriers
Uniport
Symport
Antiport
Osmosis
Transport mediated by channels
Ligand-gated ion channels
Voltage-gated ion channels
Membrane potential
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1. BASIC TYPES OF MEMBRANE
TRANSPORT:
• Diffusion: it depends on membrane permeability, along
concentration gradient
• Transport mediated by transport proteins: specific [FIG.]
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2. DIFFUSION OF SUBSTANCES ACROSS
MEMBRANE:
Diffusion of substances across membranes is selective: small
hydrophobic molecules (including gas molecules) and small uncharged
polar molecules (including H2O) [FIG.]
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3. PASSIVE VS. ACTIVE TRANSPORT
MEDIATED BY TRANSPORT PROTEINS:
• Passive transport: along concentration gradient (without
expenditure of energy)
• Active transport: against concentration gradient (expenditure of
energy)
[FIG.]
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4. TYPES OF TRANSPORT PROTEINS:
• Carriers: binding of transported molecule on one side →
conformational change → transport to the other side
• Channels: channels in the membrane which enable passage of
transported molekule (mostly ion channels) [FIG.]
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5. TRANSPORT MEDIATED BY CARRIERS:
• Uniport: transport of one type of molecules
• Symport (coupled transport): cotransport of two types of
molecules in the same direction
• Antiport (coupled transport): contransport of two types of
molecules in opposite directions [FIG.]
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6. UNIPORT:
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Passive uniport (along concentration gradient): facilitated diffusion
(transport of amino acids, glucose: GLUT1) [FIG.] [FIG.]
Active uniport: ATPases (ATP-driven pumps: Ca2+ pump) [FIG.]
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6. UNIPORT:
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Passive uniport (along concentration gradient): facilitated diffusion
(transport of amino acids, glucose: GLUT1) [FIG.] [FIG.]
Active uniport: ATPases (ATP-driven pumps: Ca2+ pump) [FIG.]
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7. SYMPORT
• Passive symport (rare)
• Active symport (glucose pump)
[FIG.] [FIG.]
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8. ANTIPORT
• Passive antiport: exchange diffusion
• Active antiport (Na+-K+ pump) [FIG.]
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9. OSMOSIS
• Nature of osmosis: water diffusion from a region with lower solute
concentration to a region with higher solute concentration [FIG.]
• Osmotic pressure: definition, maintenance of osmotic balance
[FIG.] [FIG.]
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9. OSMOSIS
• Nature of osmosis: water diffusion from a region with lower solute
concentration to a region with higher solute concentration [FIG.]
• Osmotic pressure: definition, maintenance of osmotic balance
[FIG.] [FIG.]
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10. TRANSPORT MEDIATED BY CHANNELS:
• Ligand-gated ion channels: opening is regulated by ligand binding
• Voltage-gated ion channels: opening is regulated by the change of
voltage on the membrane [FIG.]
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11. LIGAND-GATED ION CHANNELS:
• Function in cells: neurotransmitters, intracellular signaling (IP3 &
calcium channels in ER membrane) [FIG.]
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12. VOLTAGE-GATED ION CHANNELS:
• Function in cell: voltage-gated Na+ channel
[FIG.]
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13. MEMBRANE POTENTIAL:
Nature of membrane potential: a difference in charge between two
sides of the membrane [FIG.]
Mechanism of membrane potential generation: a leakage of K+ from the
cell along concentration gradient [FIG.]
Electrochemical gradient: the sum of concentration gradient and
membrane potential representing driving force for ions to cross the
membrane [FIG.]
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13. MEMBRANE POTENTIAL:
Nature of membrane potential: a difference in charge between two
sides of the membrane [FIG.]
Mechanism of membrane potential generation: a leakage of K+ from the
cell along concentration gradient [FIG.]
Electrochemical gradient: the sum of concentration gradient and
membrane potential representing driving force for ions to cross the
membrane [FIG.]
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13. MEMBRANE POTENTIAL:
Nature of membrane potential: a difference in charge between two
sides of the membrane [FIG.]
Mechanism of membrane potential generation: a leakage of K+ from the
cell along concentration gradient [FIG.]
Electrochemical gradient: the sum of concentration gradient and
membrane potential representing driving force for ions to cross the
membrane [FIG.]
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LITERATURE:
• Alberts B. et al.: Essential Cell Biology. Garland Science. New York
and London, pp. 387-423, 2010
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