Cell Membrane
I.
HOMEOSTASIS: internal
“steady state” maintained
by the body
1. What is the cell membrane made of?
– Phospholipid bilayer
• Hydrophobic tails
• Hydrophilic head
II. Cell Membrane
• Homeostasis
– Steady state maintained by
the body
• Selectively Permeable
– Regulates what can come in
and out of the cell
1. Selectively Permeable
CAN EASILY PASS:
Breathing
Small, Nonpolar
– O2
– CO2
– Water (only through protein channels)
CANNOT EASILY PASS:
– Large (glucose)
– Polar ( exception is water because its so
small)
– Ion (charged)
III. Proteins in the Cell Membrane
• “Fluid Mosaic Model”
– Many proteins will help the
membrane
– Proteins drift freely
Membrane Proteins Embedded
1. Transport Proteins
2. Cell Recognition Proteinssugars hang off proteins
3. Receptors Proteinsreceive signals
4. Enzymes- proteins that
make reactions happen
Cell Recognition Proteins
• Sugars hang off of proteins in the cell
membrane
• Give us different blood types
Receptor Protein
Receptor
Protein- is a
cell membrane
protein that
receives a
signal
Transport
1. Passive Transport: Diffusion
• The movement of particles
HIGH concentration to LOW
concentration
Why?
• Molecules are always in
random motion
– Ex.
Perfume
Food coloring
Tea bag
b) Equilibrium- particles equally spread out
2. Passive Transport: Osmosis
- Diffusion of water from HIGH to LOW
concentration
Solute: Substance in solution that is dissolved
(ex. Sugar or Salt)
Solvent: Substance in solution that does the
dissolving ( ex. Water)
Hypotonic
Environment
TONICITY
Hypertonic
Environment
Isotonic
Environment
Isotonic
Diagram
97% H20
Where is the most water?
97%
H2H
O O
97%
2
Same
Which way does water go?
Inside and outside
Result?
Big words
Examples
Even, same concentration
overall
“dynamic equilibrium”
“homeostasis
contact lens
solution, Gatorade
Hypotonic
Diagram
92 % H20
Where is the most
water?
97% H2O
Outside
Which way does
water go?
Inside
Result?
Burst, get bigger; firm
Big words
Examples
“cytolysis”- to burst; “turgid”- get firm;
“turgor pressure” :pressure inside plant
cells to help stand upright
- Distilled water ( 100% Water)
- Plants standing upright
Hypertonic
Diagram
97% H20
Where is the most water?
Which way does water go?
Result?
Big words
Examples
80% Water
Inside
Outside
Smaller, shrink, go limp
“plasmolysis”- to wilt, shrivel, loss of
pressure; “flaccid”- go limp
Candy, sugar, salt on
bushes/grass, gargle with salt
water
Hypertonic
Red Blood Cells
Check Yourself
Is the lettuce in a hypertonic isotonic hypotonic
environment and why??
Poll
Passive Transport:
3. Facilitated Diffusion
Facilitated Diffusion
- diffusion across a
membrane through
transport proteins
a) Ex. sugars, ions ,
alcohol
b) NO ENERGY: From HIGH to LOW concentration
V. Active Transport
•
Movement of molecules across a membrane require
energy
• From LOW to HIGH concentrations!
a) Why?
• To maintain a certain internal environment
• To transport large molecules in/out
The water from soil
moves into roots
from HIGH to LOW.
But then eventually,
the roots will have
more water. To
prevent the water
from going back out,
the tree uses ACTIVE
TRANSPORT to keep
pumping more water
in.
H2O
H2O
H2O
H2O
H2O
H2O
Active Transport
C) Some Types of Active Transport
1. Exocytosis
- Removal of materials
- Vesicle fuses with membrane,
forcing contents out
Active Transport
2. Endocytosis
• process of taking in
materials by infolding of the
cell membrane, forming a
vesicle
• Ex.
• Phagocytosis: Large
particle/food
• Amoeba
VI. Concentration Gradient
measurement of how the concentration of
something changes from one place to another
Passive Transport:
molecules go DOWN concentration gradient
from HIGH to LOW concentration
Active Transport:
molecule go UP concentration gradient from
LOW to HIGH concentration
Example of DOWN
concentration gradient:
Example of UP concentration
gradient:
Students going from classrooms
into hallways for next class
At a concert, moving into the
crowd towards crowded stage
• Review Video of Transport
• Why does a plant like hypotonic but an animal
does not?
• http://www.phschool.com/science/biology_pl
ace/labbench/lab1/watpot.html
Elodea Plasmolysis
http://www.youtube.com/watch?v=2
Th0PuORsWY
“Egg”citing “Eggs”periment
Cell membrane
Egg Lab: Osmosis