Download Plama Membrane

PLASMA MEMBRANE
FUNCTIONS OF THE PLASMA MEMBRANE
1. Provides a boundary between a cell and its
environment
2. Controls the flow of material in and out
of the cell
A. The membrane is selectively permeable,
which means that it lets some substances pass
through, but not everything. (selective)
3. Maintains homeostasis: balance within the cells
A. Allows more water and food to come in when
needed, gets rid of what is not needed
RELATING THE STRUCTURE TO ITS
FUNCTION
1. The membrane is a bilayer (2 layers).
 2. Made up molecules which are a glycerol
backbone, 2 fatty acids, and a phosphate group;
called the phospholipid bilayer.
 3. The polar head and nonpolar tail – fatty areas
that attract and repel water.



A. make the membrane behave like a fluid
4. Embedded proteins: determine which
molecules can go in and out of the cell.
A. Proteins serve as recognition markers
 B. Carbohydrates serve as cell identification tags

THE FLUID MOSAIC MODEL

The phospholipid bilayer allows other molecules
to “float” in the membrane.

Think of the phospholipids in the bilayer as creating
a “sea” where other molecules can float on top, like a
barrel of apples floating on top of the water.
PROTEINS IN THE PLASMA MEMBRANE
Transmit signals inside the cell
 Act as a support structure
 Provide pathways for substances to enter and
leave.

CHOLESTEROL IN THE PLASMA
MEMBRANE

Prevents fatty acid tails from sticking together
CARBOHYDRATES IN THE PLASMA
MEMBRANE

Identify chemical signals
PASSIVE TRANSPORT
1. Passive Transport - Particles move from
an area of high concentration to an area of
low concentration.
A. Cell does not require an input of energy .
B. “Facilitated diffusion”
C. Ex. When you leave the classroom you will
all go the same direction down the hallway
(ex. Diffusion)
•There
•
•
•
are 3 modes of passive transport:
1. Diffusion
2. Facilitated Diffusion
3. Osmosis
DIFFUSION

Diffusion – the net movement of particles from an
area of high concentration to an area of low
concentration

A. Difference in the concentration is called a gradient
Initial Conditions:
Diffusion takes
place:
DIFFUSION IN A CELL
FACILITATED DIFFUSION
FACILITATED DIFFUSION -THE MOVEMENT OF
MATERIALS ACROSS THE PLASMA MEMBRANE USING PROTEINS.
Channel Proteins
Carrier Proteins
OSMOSIS
OSMOSIS

Osmosis – the diffusion of water across a
selectively permeable membrane.
3 TYPES OF
SOLUTIONS:
1. Isotonic
2. Hypotonic
3. Hypertonic
ISOTONIC SOLUTIONS
A. Solutions where the concentration of solutes
and water is equal to/the same as the normal
cells of the body and the blood
 B. Movement into the cell = movement out of the
cell: water moves in both directions (in and out)

HYPOTONIC SOLUTION
A. Concentration of solute (salt) is lower in
normal cells of the body and blood.
 B. Water will move into the cell to equalize
 C. Increases osmotic pressure: pressure that’s
generated as the water flows through the plasma
membrane
 D. Cell could burst if it takes in too much water.

HYPERTONIC SOLUTIONS
A. Concentration of the solute outside of the cell
is higher than inside the cell.
 B. Water rushes out of the cell
 C. Can result in the cell shrinking – water goes
out of plant cell causing it to wilt

ACTIVE TRANSPORT
Move from an area of low
concentration to an area of high
concentration – transport against the
gradient
A. Requires energy to move items into
the cell
B. Ex. Everyone going down the
hallway in the same direction except
for you, must exert energy to get past
everyone.
ACTIVE TRANSPORT USING CARRIER
PROTEINS
TYPES OF ACTIVE TRANSPORT
PUMPS
Na+/K+

ATPase pump
Moves three Na+ ions out of the cell and
two K + ions into the cell to maintain the
level of these ions inside and outside of
the cell.
 ADD
DEMONSTRATION OF NA/K
PUMP HERE
Active Transport: Na+/K+ Pump
ATPase pump protein
gets phosphorylated by
ATP.
Protein’s conformation
changes...
causing binding & then
release of ions.
ENDOCYTOSIS
 The
process by
which the cell
surrounds and
takes particles
into the cell.
 Phagocytosiscellular eating
 Pinocytosiscellular drinking
EXOCYTOSIS
 Secretion
of
material out of
the cell through
the plasma
membrane
 Example: when
you yawn or cry,
the tear ducts
export salt from
the glands
COMPARING ENDOCYTOSIS AND
EXOCYTOSIS
Endocytosis:
Surrounds and
takes
substances into
the cell
Transports
substances
too large to
move across
the plasma
membrane
Exocytosis:
Surrounds and
expels or
secretes
substances