Download The plasma membrane

Standard B-2.2
THE PLASMA MEMBRANE
HOMEOSTASIS

The process of maintaining balance in an
organism’s internal environment .

Essential to the survival of a cell.

Maintaining homeostasis a primary job of the
plasma membrane. (does this by being
semipermeable)
PLASMA MEMBRANE

Defined as a flexible boundary between a cell
and it’s environment.
 ALL
prokaryotic and eukaryotic cells have a
plasma membrane to separate them from their
watery environment.
 The membrane allows nutrients into the cell
and allows waste and other products to leave
the cell.
PLASMA MEMBRANE
The plasma membrane has the property of
selective permeability.
 (also called semipermeable)
 This is how homeostasis is maintained.


Means:

Allows some substances to pass through to the inside
Does not allow some substances to pass though to the inside
Doesn’t allow just anything to leave the cell either.

It is selective in what it lets enter and leave the cell


Fish net
Coffee filter
Flour sifter
Gold Mining too
ANALOGIES FOR SELECTIVE PERMEABILITY
Most of the
molecules in
the PM are
phospholipids.
STRUCTURE OF THE PLASMA MEMBRANE
STRUCTURE OF THE PLASMA MEMBRANE

PM is composed of a phospholipid bilayer.

(2 layers of phospholipids are arranged tail-totail.)
THE PHOSPHOLIPID BILAYER
Each
phospholipid is
diagramed as a head with 2
tails.
PHOSPHOLIPIDS

Heads:
made polar by the phosphate group
 Is attracted to water bc water is polar too
 Hydrophilic = water loving

 Tails:
Nonpolar
Repelled
by water
Hydrophobic = water fearing
PHOSPHOLIPID BILAYER

The layers make a sandwich so that the fatty
acid tails make up the inner most portion of the
PM.
 Water
loving heads are in contact with the water
inside of the cell and the watery outside of the cell.
 Water fearing tails are farthest away from the water
they hate.
 Not
cell.
touching the water on the inside or the outside of the
OTHER COMPONENTS OF THE PM
Moving
with and among the
phospholipids are:
- cholesterol
- carbohydrates
- proteins
OTHER COMPONENTS OF THE PM
Cholesterol:
-prevents the fatty-acid tails from sticking
together.
- contributes to the fluidity of the pm.
(A high cholesterol diet is not advised, but
cholesterol plays a critical role in membrane
structure.)

OTHER COMPONENTS OF THE PM
Carbohydrates:
- Stick out from pm to define the cell’s
characteristics
- Helps cells identify chemical signals.
(Carbs in membrane might help disease-fighting
cells recognize and attack a potentially harmful
cell.)

OTHER COMPONENTS OF THE PM
Proteins:
-2 types of proteins found in PM
1. peripheral proteins
2. integral proteins
OTHER COMPONENTS OF THE PM

Peripheral proteins: proteins that do not
protrude from the inside of the cell to the
outside of the cell.
 Outer
surface: called receptors and they transmit
signals from outside the cell to the inside of the cell
 Inner surface: anchor the pm to the cells internal
support structure, gives the cell it’s shape.
OTHER COMPONENTS OF THE PM

Integral proteins: span the entire membrane,
creating tunnels through which certain
substances can enter and leave the cell.
 Move
needed substances in
 Move wastes out
Also called: Transport proteins
FLUID MOSAIC MODEL
The phospholipids in the bilayer create a “sea”
in which other molecules can float, like apples
floating in a barrel of water.
 “sea” concept is the basis for the fluid mosaic
model of the pm.
 The phospholipids can move sideways w/i the
membrane, just as the apples move around in
the barrel.

FLUID MOSAIC MODEL
At the same time, other components in the
membrane, like proteins, also move among the
phospholipids.
 Because there are different substances in the
pm, a pattern, or mosaic is created on the
surface.
 The components of the pm are in constant
motion, sliding past each other.

FLUID MOSAIC MODEL

Fluid: particles that can change position w/o
separating.

Mosaic: picture or pattern made of small pieces
of different colors and/or shapes.
REVIEW

What is the main function of the Plasma
Membrane?
REVIEW

What name has been given to the sea-like
movements of the plasma membrane?
REVIEW

What does hydrophobic mean?
REVIEW

Besides phospholipids, what is another
structure you may see in a plasma membrane
and what is that structures function within the
membrane?
REVIEW

What does hydrophilic mean?
REVIEW

What do we call the 2 layers of phospholipids
arranged tail to tail?