Download Cell Membrane!

Cell Membrane!
Diffusion and
osmosis
The cell membrane
• Separates the cell from its surrounding
environment
• Controls movement of materials into and
out of the cell
• Makes it possible for cell contents to be
chemically different from environment
• Maintains homeostasis
Cell Membrane
Structure of cell membrane
• Two layers bilayer made of lipid (fat)
molecules
• Hydrophilic = water loving
• Hydrophobic = water hating (fear of)
Cell Membrane
A phosopholipid is the major lipid found in the
cell membrane.
A. Each molecule has a polar head and
two nonpolar tails.
1. Because of its hydrophilic nature,
the head will orient (point) toward water.
2. Because of it’s hydrophobic nature,
the tails will orient away from water.
CELL MEMBRANE
B. Because a cell is bathed inside
and out in a watery solution, the
phospholipid molecules form
two layers, a lipid bilayer.
C. Cholesterol, a steroid, fits
between the tails of the
phosopholipid to provide
support.
CHOLESTEROL
Proteins of the cell membrane
A. Peripheral proteins are located on the
interior and exterior.
B. Integral proteins are embedded in the bilayer.
1. Some I.P. extend across the
entire cell membrane.
2. Some I.P. protrude only on one side or the
other.
3. Some I.P. have carbohydrates attached which
serve to:
a. hold adjoining cells together.
b. act as a site where viruses can attach.
c. site where hormones can attach.
4. Some I.P. have channels or pores
through which substances can pass.
5. Some I.P. bind to a substance on one
side of the membrane and carry it to
the other side.
Integral proteins
•
•
•
•
Transport or move substances
through membrane
Receptors are sites that bind special
messenger molecules that tell cell to
start or stop some chemical activity
enzymes
Bind membrane to neighbor or other
cell structures
CELL MEMBRANE
Scientists use the term fluid mosaic model to
describe the cell membrane.
Because of this fluidity, membrane proteins
and lipids can move laterally (side to side) within
the bilayer.
DIFFUSION
THE MOVEMENT OF MOLECULES
FROM AN AREA OF:
HIGHER
CONCENTRATION
TO AN AREA OF
LOWER CONCENTRATION.
WHAT DRIVES THE
DIFFUSION PROCESS?
THE KINETIC ENERGY
OF THE MOLECULES!
DIFFUSION AND THE CELL
MEMBRANE!
SOME
SUBSTANCES
EASILY CROSS
THE CELL
MEMBRANE,
OTHERS
CANNOT CROSS
AT ALL.
THE CELL
MEMBRANE IS:
SELECTIVELY
PERMEABLE!
Selectively Permeable:
Some substances can pass through freely
Some can pass through only to a slight
extent or at certain times
Some cannot go through at all
A cell cannot survive in
isolation.
Nutrients and waste
must pass through the
cell membrane.
THE DIFFERENCE IN
CONCENTRATION OF
MOLECULES ACROSS A
SPACE IS CALLED:
CONCENTRATION
GRADIENT
WHAT CAUSES THIS TO
TAKE PLACE?
Concentration is
most at the top
of the hill
PASSIVE TRANSPORT
SOME SUBSTANCES CAN CROSS THE
CELL MEMBRANE WITHOUT ANY
IMPUT OF ENERGY BY THE CELL.
THE SIMPLIST TYPE OF PASSIVE
TRANSPORT IS:
EQUILIBRIUM
WHEN THE
CONCENTRATION OF THE
MOLECULES OF A
SUBSTANCE IS THE SAME
THROUGHOUT!
WILL MOVEMENT
STILL
CONTINUE?
IN WHICH
DIRECTION?
OSMOSIS
THE PROCESS BY WHICH WATER
MOLECULES DIFFUSE ACROSS A CELL
MEMBRANE FROM AN AREA OF HIGHER
CONSENTRATION TO AN AREA OF LOWER
CONSENTRATION!!!
PASSIVE TRANSPORT
DIRECTION OF OSMOSIS
DEPENDS ON THE CONCENTRATION OF THE
SOLUTES ON THE TWO SIDES OF THE
MEMBRANE.
HYPOTONIC
HYPERTONIC
Suppose you put a cell into a
glass of salt water.
NaCl above normal
NaCl normal
Water moves out of the cell
Cell shrinks
Suppose you put a cell into a glass of
less salt water (hypotonic)
NaCl below normal
NaCl normal
Water moves into cell
ANIMAL
PLANT
If the solution is isotonic relative to the cell, then
the solute concentrations are the same on both
sides of the membrane and water moves equally in
both directions
A hypertonic solution has increased solute, and a
net movement of water outside causing the cell to
shrink.
A hypotonic solution has decreased solute
concentration, and a net movement of water inside the
cell, causing swelling or breakage.