Download The Cell Membrane

THE CELL
MEMBRANE
ONLY 2
MOLECULES THICK, THIS MEMBRANE
ALLOWS THE PASSAGE OF ESSENTIAL MOLECULES
IN AND OUT OF THE CELL.
DEFINITION:
A cell membrane functions as a selective barrier
that allows sufficient passage of oxygen,
nutrients, and wastes to service the entire
volume of the cell.
 The cell membrane is located at the boundary of
every cell. It is composed of phospholipids and
proteins
 The membrane building blocks are phospholipids
containing hydrophilic and hydrophobic parts.
 Every cell has a plasma membrane.


Maintain a steady environment: Homeostasis
THE CELL MEMBRANE

The fluid mosaic model (S.J Singer)
it is semi-permeable (some items are allowed in,
others aren’t..it’s picky!)
 fluid portion is a double layer of phospholipids, called
the phospholipid bilayer

JOBS OF THE CELL MEMBRANE
(THINK OF A POLICE OFFICER!)
1.
To isolate the cytoplasm from the external
environment.
2.
Regulate the exchange of substances into and
out of the cell.
3.
To communicate with other cells.
4.
To identify proteins required by the cell.
WHAT THE CELL
MEMBRANE IS MADE UP OF
Composed of a phospholipid bilayer with a collage of
many different proteins, lipids and carbohydrates.
 A Phospholipid is composed of 1 glycerol molecule, 2
fatty acids and 1 phosphate group. This structure
causes hydrophilic and hydrophobic regions.

Phospholipids contain a hydrophilic head and a nonpolar hydrophobic tail.
 Hydrophobic interactions force the "tails" to face
inward.

The heads are hydrophillic (like water)
 The tails are hydrophobic (afraid of water)

DRAW AND LABEL!
LAYER MAKE-UP!

The phospholipids are not bonded to each other,
instead the heads line up beside each other
packed together like sardines. Because the
heads are close together, the membrane is said
to be fluid...it can bend and twist and break off
to form vesicles.
LAYER MAKE-UP!

The membrane is also super strong thanks to
cholesterol molecules that are embedded in the
membrane makes it stronger.
SO HOW DO MOLECULES GO FROM THE
CYTOPLASM TO THE EXTRACELLULAR FLUID?
5 VERY IMPORTANT PROTEINS!
1.
Channel Proteins - form small openings for
molecules to diffuse through. There are two
types of channel proteins (open channel
proteins and gated channel proteins). Similar to
a tunnel water slide...if the slide is open and you
can fit...you can go through!
PROTEINS PROTEINS
PROTEINS! WOW!
AND
MORE
2. Carrier or Transport Proteins- binding site on
protein surface "grabs" certain molecules and
pulls them into the cell.
PROTEINS PROTEINS
PROTEINS! WOW!
AND
MORE
3. Receptor Proteins - molecular
triggers that set off cell responses
(such as release of hormones or
opening of channel proteins). Must
be activated on one side of the cell
membrane, to release something on
the other side.
PROTEINS PROTEINS
PROTEINS! WOW!
AND
MORE
4. Cell Recognition Proteins - ID tags, to identify
cells to the body's immune system. Very similar
to security at the dance.
THE LAST IMPORTANT PROTEIN
FOR NOW!
5. Enzymatic Proteins - carry out metabolic
reactions. There are different protein enzymes
for every biochemical function in the body.
These special proteins need to be activated
before they are turned on.
Construction of a Cell Membrane
http://www.wisconline.com/objects/index_tj.asp?objID=AP1101