Unformatted text preview: and Cl-, by shuttling them across the membrane. • Substances do not move across the barrier
indiscriminately; membranes are selectively
10:25 Gardiner 2013 27 9 !permeability&depends&on&interaction&of&molecule&at&the& • Permeability of a molecule through a
membrane depends on the interaction of
that molecule with the hydrophobic core of
the membrane. hydrophobic&core – Hydrophobic molecules, CO2, and O2, can
dissolve in the lipid bilayer and cross easily.
– Ions and polar molecules pass through with
– Proteins can assist and regulate the transport 10:25 Gardiner 2013 28 • Specific ions and polar molecules can
cross the lipid bilayer by passing through
transport proteins that span the
– Some transport proteins have a hydrophilic
channel that certain molecules or ions can use
as a tunnel through the membrane.
– Others bind to these molecules and carry their
passengers across the membrane physically. !transport&proteins&are&necessary&to&get&things&across&
!Each&transport&protien&is&speci:ic&to&ONE&thing • Each transport protein is specific as to the
substances that it will translocate (move).
10:25 Gardiner 2013 29 • For example, Paramecium, a protist, is
hypertonic when compared to the pond
water in which it lives.
– In spite of a cell membrane water still
continually enters the Paramecium cell.
– Paramecium have a
the contractile vacuole,
that functions as a bilge
pump to force water out
of the cell. 10 Specific proteins facilitate passive
transport of water and selected solutes Facilitated*diffusion:
membrane • Many polar molecules and ions that are
normally impeded by the lipid bilayer of the
membrane diffuse passively with the help of
transport proteins that span the membrane.
• The passive movement of molecules down
its concentration gradient via a transport
protein is called facilitated diffusion.
10:25 Gardiner 2013 !N...
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