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Chapter 2

BIOL 361 Chapter Notes - Chapter 2: Second Messenger System, Potassium Channel, Cytoskeleton

Course Code
BIOL 361
James( Jim) Cooke

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Week 2B Learning Objectives
Ion channels are membrane proteins that form pores for specific ions to pass when the channel is open. The
channels are specific to one or sometimes two ions. The specificity of transport is due to a structural
component of the channel: selectivity filter.
LO1. Differentiate between leak ion channels and gated ion channels
Leak ion channels
Gated channels
Always open
Determines the resting membrane
potential of cells
Can be opened and closed in
response to stimulus
Three types, can be opened by
changes in voltage (voltage-gated),
binding of chemical messengers
(ligand-gated), changes in mechanical
force echaogated…etc.
LO2. Identify the types of ion gated channels (leak channels & voltage-, ligand-mechano- gated channels
Leak channels
Cell membranes have intrinsic permeability to ions, even at rest, due to the presence of leak channels. Ions
will move down their electrochemical gradients (toward their equilibrium potential) through these leak
channels. Active pumping by the Na+/K+ ATPase is needed to compensate for the leakage of Na+ and K+ ions.
Voltage-gated channels
Change in Vm open and/or close the channels
Ligand-gated channels
Ligand binds to the channel and causes a conformational change which opens an ion channel within the
proteina route for the ion to move across the membrane. When the ion channel opens, the ions move into
or out of the cell as dictated by electrochemical gradients.
Receptor site: made of amino acids located on folds of subunits; high affinity for ligand
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