Cell Membrane
Function of Cell Membrane
 Separates
the cell’s contents from
materials outside the cell
 Regulates what moves in and out of a cell
 *without the cell membrane to contain the
substances the cell needs for life, the cell
would die.
Structure of Cell Membrane
 -composed
of groups of organic
compounds (glycolipids,
glycoproteins, proteins, cholesterol,
and phospholipids)
 Phospholipid – shaped like a head
with 2 tails
 -made from a phosphate group
connected to 2 fatty acid tails (forms a
double layer called a lipid bilayer)
Structure of Phospholipid
Why are the phospholipids
arranged tail to tail?
 -b/c
water is inside and outside the
cell
 phosphate group is hydrophilic (polar)
end
-attracts water
 fatty acid tail end is hydrophobic
(nonpolar)
-repels water
Arrangement of phospholipids
“tail to tail”
Polar vs. Nonpolar
 Polar-
positive and negative ends (b/c
electrons are not shared equally)
Ex. Water
 Nonpolar- does not have oppositely
charged ends (atoms share electrons
equally)
Arrangement of phospholipids
“tail to tail” due to water inside &
outside the cell
Fluid Mosaic Model of Cell
Membrane
 -lipid
bilayer is not strong & firm like a
hard shell, but it is fluid like a soap
bubble (often called a fluid mosaic
model)
 -individual phospholipids, arranged
side by side, float within the bilayer
(cholesterol prevents phospholipids
from sticking together)
Structure of Cell Membrane
 -nonpolar
interior zone- true barrier
that separates the cell from its
surroundings
 many polar particles like sugars,
proteins, ions, & most cell wastes
cannot cross this zone b/c they are
repelled by the nonpolar region
What’s in the cell membrane?
 Solution?
 -passageways
through the barrier that
enable the cell to regulate what
substances go in and out.
 Cell Surface Proteins- proteins
embedded within the plasma
membrane of cells
 Proteins- 50% to 70% of cell
membrane
Types of Cell Surface Proteins
Proteins- act as “gates” to
the cell interior, transporting food &
other molecules (sugar, proteins,
ions) in & wastes out
 Channel
Types of Cell Surface Proteins
 Receptor
proteins- information receivers
they are the informers of the cell,
gathering information about the cell’s
surroundings
 *many hormones act by binding to specific
receptor proteins
 Ex. Glycoproteins- combination of protein
and carbohydrates
 Ex. Integral proteins- span entire range of
cell membrane
Types of Cell Surface Proteins
proteins- “name tags of the cell”
identifies what kind of cell it is (ex. Liver
cell, heart cell, or brain cell)
 marker proteins have long exterior arms
that often have carbohydrates attached to
them
Ex. Glycoproteins or glycolipids
 Marker
Arrangement of cell surface
proteins
Cell Membrane Structure