THE FLUID MOSAIC MODEL
Plasma Membrane – aka cell membrane
What is it?
What is it made of?
What is its function?
Cell Membrane Structure:
- A mosaic of lipids, proteins and carbohydrate,
embedded in a fluid bilayer of phospholipids
Cell Membrane Function:
a.Controls what enters/exits a
cell - maintains an internal
balance called homeostasis
b. Provides protection and
support for the cell
Structure of the Cell Membrane
Outside of cell
Proteins
Lipid
Bilayer
Transport
Protein
Animations
Go to
of membrane
Section:
Carbohydrate
chains
Phospholipids
Inside of cell
(cytoplasm)
Polar heads
love water
Fluid Mosaic
Model of the
cell membrane
Non-polar
tails hide
from water.
Carbohydrate cell
markers
Proteins
Membrane
movement
animation
HOW DOES THE MEMBRANE MOVE?
 A membrane is held in together by weak
hydrophobic interactions.
Most membrane lipids and some proteins can
drift laterally within the membrane
 Molecules rarely flip
transversely (flip-flop) across
the membrane, because
hydrophilic parts would have
to cross the membrane’s
hydrophobic core.
Why is fluidity important?
Membrane must be fluid to work properly.
Solidification may result in permeability changes
Unsaturated hydrocarbon tails enhance membrane
fluidity because kinks at the carbon-to-carbon double
bonds hinder close packing of phospholipids.
What else helps to keep membrane fluidity?
Cholesterol
Cholesterol allows the cell membrane to stay fluid (esp. when
temp drops), while at the same time keeping the cell from
becoming too fluid (when temp rises) that it can no longer hold
its shape