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BIOL 331 CMMB
Cell membranes
Membrane transport
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methods of passive transport:
channels
,
simple diffusion
, through a
facilitative transporter
methods of active transport:
Pumps
Simple diffusion
allows small inorganic solutes such as
O2
,
Co2
, and
H2O
to pass through the
bilayer.
They also have a
high lipid solubility.
Hypertonic
solution:
higher
solute conc'
outside
of the cell
Hypotonic
sol'n:
lower
solute con'c
outside
of cell
Simple
diffusion
through a channel:
aquaporin
:
channel
protein that allows
water
through
quicker
than just by
diffusion
through the
bilayer
ion
channels:
transmembrane
structure
permeable
to a specific ion or ions.
most ion channels are
gated
: require a
change
in
conformation
to
open
/
close
Types of ion channels:
Voltage-gated
: open/close based on the
difference
in charge across the
2
sides of the membrane
ligand-gated
: open/close depending on the
binding
of a specific molecule (ligand) that is usually not the solute passing through the channel
Mechano-gated
: open/close depending on
mechanical
forces (eg, stretching, soundwaves, etc)
Is a facilitative transporter passive or active transport?
Passive
is transport through a channel or bilayer passive or active?
passive
Facilitative transporter
Binding of the solute triggers a
conformational
change in the
transmembrane
protein that exposes the solute to the other side.
the transporter is specific to the molecule transported
exhibits saturation-type kinetics because the have to undergo a
conformational
change
Practice question (select letter)
f
Primary active transport:
pumps
three types:
P-type
pump: pump becomes
phosphorylated
during active transport
V-type pump: transports
hydrogen
ions across organelles and
vacuoles
ABC
transporter:
ATP-binding-cassette
transporters; share a similar of
ATP
binding domain and transport
ions
, lipids, peptides, and nucleotides.
Per ATPin Na+/K+ ATPase
3
Na+ transported out of the cell
2
K+ ions pumped into cell
View source
Na+/K+ ATPase
Step 1:
E1
conformation:
high
affinity for Na+, pump faces the
cytosol.
ATP is bound.
Step 2: Ion is bound, protein
closes
(occluded E1)
Step 2-3: Hydrolysis of
ATP
, pump is
phosphorylated
with phosphate from ATP. ADP and
P
still bound.
Step 3-4: Release of
ADP
triggers change to
E2
conformation. Pump faces the
extracellular
side,
low
affinity of Na+ and
high
affinity for K+.
Step 5-6: Ion is bound, protein closes (occluded
E2).
Dephosphylation
.
Step 7-8: ATP binds, protein returns to
E1
and there is
high
Na+ affinity
View source
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