Cell Membrane
What is it made of?
How does it work?
Cell Membrane
• Cell membrane is made up of two parts
– It is made up of lipids (fat molecules) and proteins.
Phospholipid part (75-95%)
Protein part (5-25%)
• Protein Part of Cell provides
 Communication
 I.D. tags
 Anchors
 Gates to exchange large molecules
 Pumps
Cell membrane proteins
– Channel proteins- allow molecules or ions to enter
cell
– Receptor proteins-relay information from outside
the cell to inside the cell
– Marker proteins-act as the name tags of the cell
Questions?
• What type of proteins
would you expect to
be present in the
following cells?
• Red blood cell
• Brain cell
• Kidney cell
• Tongue cell
• Marker proteins
because of the blood
group antigens
• Receptor proteins for
transferring
information
• Channel proteins to
help filter out wastes
• Receptor proteins for
detecting food
molecules
• Cell Membrane is
– Known as the Fluid Mosiac Model
 All of the molecules “float” around, exchanging
positions
 Membrane has flexibility
 Tiny spaces between membrane molecules allow
certain materials to enter or leave the cell
 http://www.stolaf.edu/people/giannini/biological%20anamations.html
 The membrane is "selectively permeable", meaning it selects what
substances enter or leave.
 In other words, not all substances are allowed to pass through
the membrane.
Transportation of Molecules
• Passive Transport
-no energy required
-Molecules move high to low conc.
1. Diffusion
2. Facilitated Diffusion
3. Osmosis
a. Hypoonic
b. Hypertonic
c. isotonic
•Active Transport
-needs ENERGY
-Molecules move low to high conc.
A. Endocytosis
1. Pinocytosis
2. Phagocytosis
B. Exocytosis
•
Diffusion
Molecules moving from an area of
high concentration to an area of low
concentration
– Random motion drives diffusion
– Movement is based on kinetic
energy (speed), charge, and
mass of molecules
– Equilibrium is reached when
there is an even distribution of
solute molecules
Review:
-Solute is the substance being
dissolved (example salt)
-Solvent is the substance doing the
dissolving (example water)
(water)
Osmosis:
The net movement of water
molecules along a concentration
gradient from an area of high water
concentration to an area of low water
concentration through a selectively
permeable membrane.