PowerLecture:
Chapter 5
A Closer Look at Cell
Membranes
Impacts, Issues: One Bad
Transporter and Cystic Fibrosis
 CFTR
is a protein channel for chloride ions
 CFTR is a type of ABC transporter in all
prokaryotic and eukaryotic cells
ATP
ATP
Fig. 5.2, p.75
Impacts, Issues: One Bad
Transporter and Cystic Fibrosis
 Cystic
fibrosis, the most common fatal
genetic disorder in the U.S., results from a
mutation in CFTR gene
Section 5.1: Lipid Bilayer

Basic framework

Selectively permeable

Two layers of
phospholipids
http://www.bioteach.ubc.ca/Bioindustry/Inex/graphics/lipidbilayer.gif


Hydrophilic heads
Hydrophobic tails
Fluid Mosaic Model
 Every
cell membrane has a mixed
composition of phospholipids, glycolipids,
sterols, and proteins
 Most
phospholipids and some proteins can
drift through membrane
Overview of
Membrane Proteins
Receptor
Proteins
Recognition
Proteins
Passive
Transporters
Active
Transporters
Fig. 5.6, p.79
Overview of
Membrane Proteins
Adhesion
Proteins
Communication
Proteins
Fig. 5.6, p.78
Transport Proteins
 Span
the lipid bilayer
 Passive


Ion selective (nerve and muscle cells)
Change shape when they interact with solute
• GluT1 (glucose transporter)

Cotransporter
 Active

Pump solute (calcium pump, ATPase)
Other Proteins
 Receptor
-- Bind an extracellular substance
that triggers changes in cell activity

Antibody
 Recognition

HLAs for tissue defense
 Adhesion

– ID tags for species
– one cell bind to another
collagen
 Communication

– channel between 2 cells
Cardiac gap junction
Section 5.3:
Concentration Gradient
 Different
in #/unit
volume of a
substances
between 2 regions
 Will move down
“down” gradient
Diffusion
 Movement
of like
molecules or ions
down a gradient
 Molecules
move on
their own gradient
Factors Affecting
Diffusion Rate

Steepness of concentration gradient


Molecular size


Smaller molecules, faster diffusion
Temperature


Steeper gradient, faster diffusion
Higher temperature, faster diffusion
Electrical or pressure gradients
Cell Membranes Show Selective
Permeability
 Some
substances
enter, but not others
 Vital to maintaining
homeostasis
 Allows NP
 Impermeable to ions
& lg Polar
Section 5.5:
Osmosis

Diffusion of water molecules across a
selectively permeable membrane
• Direction of net flow is
determined by water
concentration gradient
• Side with the most
solute molecules has
the lowest water
concentration
water molecules
semipermeable membrane
between two compartments
protein molecules
Tonicity
Refers to relative solute concentration of
two fluids
Hypotonic - having fewer solutes
Hypertonic - having more solutes
Isotonic - having same amount
Tonicity and
Osmosis
2%
sucrose
solution
1 liter of
distilled water
1 liter of
10% sucrose
solution
Hypotonic
Conditions
Hypertonic
Conditions
1 liter of
2% sucrose
solution
Isotonic
Conditions
Fig. 5-13, p.85
What type of solution are these cells in?
A
B
C
Hypertonic
Isotonic
Hypotonic
Pressure and Osmosis
 Hydrostatic


Pressure exerted by fluid on the walls that
contain it
The greater the solute concentration of the
fluid, the greater the hydrostatic pressure
 Osmotic

pressure
pressure
Amount of pressure necessary to prevent
further increase of a solution’s volume
How Organisms Deal
with Osmotic Pressure
•A protist like paramecium has contractile vacuoles that
collect water flowing in and pump it out to prevent them
from over-expanding.
How organisms deal with
Osmotic Pressure
•
•
Salt water fish pump salt out of their
specialized gills so they do not dehydrate.
Animal cells are bathed in blood. Kidneys
keep the blood isotonic by remove excess
salt and water.
 Bacteria and plants have cell walls that
prevent them from over-expanding. In
plants the pressure exerted on the cell wall
is called tugor pressure.
Increase in Fluid Volume
first
compartment
hypotonic
solution
second
compartment
hypertonic
solution
membrane
permeable to
water but not to
solutes
fluid volume
rises in
second
compartment
Fig. 5.14, p.85
Section 5.4:
Passive Transport
 Flow
of solutes through the interior of
passive transport proteins down their
concentration gradients
 Passive
transport proteins allow solutes to
move both ways
 Does
not require any energy input
Passive Transport
glucose transporter
solute (glucose)
high
low
Stepped Art
Fig. 5.10, p.80
Facilitated Diffusion
 Help
move specific solutes down the
gradient
 Can be gated
Active Transport
 Net
diffusion of solute is against
concentration gradient
 Transport
protein must be activated
 ATP
gives up phosphate to activate
protein
 Binding
of ATP changes protein shape
and affinity for solute
Active
 Help
specific solutes diffuse against the
gradient
Active Transport
higher calcium
concentration
ATP
Pi
ADP
Stepped Art
Fig. 5-11, p.83
Active Transport
 ATP
gives up phosphate to activate
protein
 Binding
of ATP changes protein
shape and affinity for solute
Types of Cellular Transport
Passive Transport
cell doesn’t use energy

1.
2.
3.
Diffusion
Facilitated Diffusion
Osmosis
high
low
Active Transport
cell does use energy

1.
2.
3.
Protein Pumps
Endocytosis
Exocytosis
•Animations of
Active Transport
& Passive
Weee
Transport
e!!!
high
This is
gonna
be
hard
work!!
low
Other types
Endocytosis (vesicles in)
Exocytosis (vesicles out)
Fig. 5-9, p.81
Section 5.6:
Endocytosis and Exocytosis
 Exocytosis:
A cytoplasmic vesicle fuses
with the plasma membrane and contents
are released outside the cell
Endocytosis
A
small patch of plasma membrane sinks
inward and seals back on itself, forming a
vesicle inside the cytoplasm – membrane
receptors often mediate this process
Macrophage engulfing
Leishmania mexicana
parasite
macrophage
Fig 5.17, p.87
endocytosis
a
exocytosis
5.6 Traffic to
and From the
Cell
coated pit
b
d
e
c
f
Endocytosis
and Exocytosis
Fig. 5-15, p.86
How Proteins Get to the Surface
vesicle membrane
fuses with plasma
membrane
Golgi body
endoplasmic reticulum
Fig. 5.18, pg. 87
Endocytosis of cholesterol
plasma membrane
cholesterol