CELL MEMBRANE STRUCTURE
• Phospholipid Bilayer
• Proteins (peripheral and integral)
• Carbohydrates
FUNCTIONS OF THE CELL MEMBRANE
 Protective barrier that regulates transport in & out of
cell (selectively permeable)
 Provide anchoring sites for filaments of cytoskeleton
 Contains the cytoplasm (fluid in cell)
 Maintain homeostasis (balance between inside and
out)
FLUID MOSAIC MODEL
FLUID- because individual phospholipids and proteins
can move around freely within the layer, like it’s a
liquid.
MOSAIC- because of the pattern produced by the
scattered protein molecules when the membrane is
viewed from above.
WATER AND THE MEMBRANE
Polar heads are hydrophilic
“water loving”
Nonpolar tails are hydrophobic
“water fearing”
HOW THINGS ENTER AND LEAVE THE CELL
3 different ways
 Pass directly through the membrane
 Through a transport/ channel protein
 Transport Vesicles
TYPES OF TRANSPORT
Passive Transport-(no energy required)
 Diffusion
 Osmosis
 Facilitated Diffusion
Active Transport (energy required)
 Endocytosis
 Ectocytosis
 Sodium /Potassium Pump
DIFFUSION
• Requires no energy and is a passive movement.
• Molecules move from an area of high concentration to
an area of low concentration.
• Examples: Oxygen and water going in, carbon dioxide
going out.
DIFFUSION OF LIQUIDS
DIFFUSION ANIMATIONS
http://www.stolaf.edu/people/giannini/flashanimat/transport/diffusion.swf
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion
_works.html
OSMOSIS
• Diffusion of WATER across a
membrane
• Moves from HIGH water
potential (low solute) to LOW
water potential (high solute)
• No Energy Required
http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.
swf
OSMOSIS CONDITIONS
Isotonic solutions
 When the amount of solutes is equal inside and outside of cell (cell
will stay the same)
Hypotonic solution
 When solutes outside are lower than inside cell (cell will swell) *
more water outside
Hypertonic solution
 When solutes outside are higher than inside cell (cell will shrink) *
more water inside cell
CELL SHRIVEL AND BURSTING
• If a cell has too much water inside, it will burst open or
lyse. (cytolysis)
• If a cell has more water outside the cell, it will shrivel.
(plasmolysis)
OSMOSIS IN RED BLOOD CELLS
Isotonic
Hypotonic
Hypertonic
FACILITATED DIFFUSION
• Occurs when substances are not able
to pass directly through the
membrane. (glucose)
• They enter the cell with the aid of
transport proteins.
• It occurs along the concentration
gradient and does not require energy.
http://highered.mcgrawhill.com/sites/0072495855/student
_view0/chapter2/animation__how_f
acilitated_diffusion_works.html
FACILITATED DIFFUSION
TRANSPORT PROTEINS
• Channel proteins are
embedded in the cell
membrane & have a pore
for materials to cross
• Carrier proteins can
change shape to move
material from one side of
the membrane to the
other
ACTIVE TRANSPORT
• Requires energy
• Substances cannot pass directly
through the cell membrane.
• Moves against the gradient from LOW
to HIGH Concentrations.
• The proteins pump molecules through
the cell membrane. REQUIRES
ENERGY in the form of ATP.
ACTIVE TRANSPORT
Some molecules that are pumped across the membrane
include
 Sodium, Potassium, and Calcium Ions
ACTIVE TRANSPORT
SODIUM-POTASSIUM PUMP
Most common example of
active transport.
Uses energy to pump sodium
and potassium ions
through the membrane.
3 Na in; 2 K out
ENDOCYTOSIS/ EXOCYTOSIS
• If the molecules are too large to pass through the
membrane, they must use a vesicle to enter and exit.
BULK TRANSPORT
• Endocytosis – Big stuff entering
• Exocytosis- Big stuff leaving