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Transcript
CELL MEMBRANE
FUNCTION
PASSIVE DIFFUSION, OSMOSIS,
FACILITATED DIFFUSION AND ACTIVE
TRANSPORT
The Cell Membrane
Question of the Day:
How Is the Structure of a Membrane
Related to Its Function?
MEMBRANE PROTEINS
Signaling molecule
Enzymes
ATP
(a) Transport
Receptor
Signal transduction
(b) Enzymatic activity
(c) Signal transduction
(e) Intercellular joining
(f) Attachment to
the cytoskeleton
and extracellular
matrix (ECM)
Glycoprotein
(d) Cell-cell recognition
N-terminus
C-terminus
 Helix
EXTRACELLULAR
SIDE
CYTOPLASMIC
SIDE
Importance
ER
1
1. Acquire
molecules &
Ions
2.Transport
into and out
of cell
through
membrane
Transmembrane
glycoproteins
Secretory
protein
Glycolipid
Golgi
2
apparatus
Vesicle
3
4
3.Transport
WITHIN the
cell
Secreted
protein
Plasma membrane:
Cytoplasmic face
Extracellular
face
Transmembrane
glycoprotein
Membrane glycolipid
Cell Membrane Function
Problems and Solutions
1. Relative concentrations
Passive Transport
Active Transport
2. Lipid bilayers are impermeable to most
essential molecules and ions
permeable to:
small non polar molecules
Cell membrane function, con’t
b. impermeable to:
-
DIFFUSION
SIMPLE DIFFUSION REQUIRES A
CONCENTRATION GRADIENT
FACILITATED DIFFUSION REQUIRES A
CONCENTRATION GRADIENT AND A PROTEIN
TRANSPORTER
Use you membrane models to show diffusion
Molecules of dye
Membrane (cross section)
WATER
Net diffusion
(a) Diffusion of one solute
Net diffusion
Equilibrium
Net diffusion
Net diffusion
(b) Diffusion of two solutes
Net diffusion
Net diffusion
Equilibrium
Equilibrium
Use your EXTRACELLULAR
models to FLUID
show
facilitated
diffusion.
Channel protein
Solute
CYTOPLASM
(a) A channel protein
What
molecules
would you
want to
transport
this way?
Carrier protein
(b) A carrier protein
Solute
ACTIVE TRANSPORT
REQUIRES A PROTEIN TRANSPORTER
AND ATP ENERGY
Active transport:
ATP
EXTRACELLULAR
FLUID
Na+
[Na+] high
[K+] low
Na+
Na+
Na+
Na+
Na+
Na+
Na+
CYTOPLASM
1
Na+
[Na+] low
[K+] high
P
ADP
2
ATP
P
3
P
P
6
5
4
–
ATP
EXTRACELLULAR
FLUID
+
–
+
H+
H+
Proton pump
H+
–
+
H+
H+
–
+
CYTOPLASM
–
H+
+
–
+
H+
ATP
–
H+
+
H+
Proton pump
H+
–
H+
+
–
H+
+
H+ Diffusion
of H+
Sucrose-H+
cotransporter
H+
Sucrose
–
–
+
+
Sucrose
REVIEW
Passive transport
Active transport
ATP
Diffusion
Facilitated diffusion
Osmosis
Passive Diffusion of Water
Vocabulary:
Hypertonic, hypotonic, isotonic, osmotic
pressure, tonicity, turgid, flaccid, lyse.
Hypotonic solution
H2O
Isotonic solution
H2O
H2O
Hypertonic solution
H2O
(a) Animal
cell
Lysed
H2O
Normal
H2O
Shriveled
H2O
H2O
(b) Plant
cell
Turgid (normal)
Flaccid
Plasmolyzed
What would happen to the animal
cells in each beaker?
100% Distilled Water
80% Water
20% Dissolved
Substances
70% Water
30% Dissolved
Substances
Which way did the water move?
80% H2O
20% “stuff”
100% Distilled Water
0% dissolved
substances
Hypotonic solution
Why did the cell get so
big?
Which way did the water move?
80% H2O
20% “stuff”
80% Water
20% Dissolved
Substances
Isotonic solution
Why did the cell stay
the same size?
Which way did the water move?
80% H2O
20% “stuff”
70% Water
30% Dissolved
Substances
Hypertonic solution
Why did the cell get so
small?
• Let’s look at what happens to your blood cells
in the three different solutions:
– Isotonic (equal)
– Hypertonic (high)
– Hypotonic (low)
“Cell”
0.03 M sucrose
0.02 M glucose
Environment:
0.01 M sucrose
0.01 M glucose
0.01 M fructose
Lower
concentration
of solute (sugar)
Higher
concentration
of sugar
H2O
Selectively
permeable
membrane
Osmosis
Same concentration
of sugar
Additional transport Mechanisms
• Bulk Transport
• Endocytosis
– Phagocytosis
– Pinocytosis
• Receptor-mediated
endocytosis
http://www.youtube.com/watch?v=PsrnMeu6sIY&feature=related
PHAGOCYTOSIS
EXTRACELLULAR
FLUID
1 µm
CYTOPLASM
Pseudopodium
Pseudopodium
of amoeba
“Food” or
other particle
Bacterium
Food
vacuole
Food vacuole
An amoeba engulfing a bacterium
via phagocytosis (TEM)
Phagocytosis
Amoeba
• Your white bloods cells also do this.
• This is the ingestion of large particles.
PINOCYTOSIS
0.5 µm
Plasma
membrane
Pinocytosis vesicles
forming (arrows) in
a cell lining a small
blood vessel (TEM)
Vesicle
Pinocytosis
• Tiny pockets form along cell membrane, and pinch
off into vacuoles inside the cell. Sometimes called
“Cell Drinking”
RECEPTOR-MEDIATED ENDOCYTOSIS
Coat protein
Receptor
Coated
vesicle
Coated
pit
Ligand
A coated pit
and a coated
vesicle formed
during
receptormediated
endocytosis
(TEMs)
Coat
protein
Plasma
membrane
0.25 µm
Exocytosis
• This is how the cell gets rid of waste.