Transcript Cells and Membranes

Cell Membrane
The Door to the Cell
Structure of the Cell Membrane
1. PHOSPHOLIPID
Head region is outward facing
Tail region is inward facing
Naturally forms 2 layers in water known as a phospholipid
bilayer
It is fluid!
Permeable only to small molecules like H2O, O2, and CO2
2. CHOLESTEROL
imbedded in the phospholipid bilayer to add strength
and stability to the membrane
3. CYTOSKELETON
fibers in the cytoplasm of the cell that help support and
give strength to the phospholipid membrane
4. CHANNEL PROTEINS (blue)
• Create ‘doorways’ through the membrane for larger
molecules like C6H12O6
• Each protein is a specific shape and only allows
certain molecules into or out of the cell
• Semi-permeable
OTHER PROTEINS:
5. RECEPTORS – Pick up chemical messages from
other cells. This triggers a reaction from the cell.
(like antennae)
6. MARKERS (self-antigens) – identify cells
(like dog-tags)
A real cell membrane
• The arrow is
pointing to the
cell membrane
The dark black lines
are the two layers
of lipids
Outside
the cell
Inside
the cell
• SOME
SUBSTANCES, ARE
SMALL ENOUGH TO
MOVE THROUGH
THE SPACES
BETWEEN THE
LIPIDS.
• NAME 4 EXAMPLES.
• OTHER MATERIALS
ARE TOO LARGE
TO FIT THROUGH
THE SPACES.
• NAME 3 EXAMPLES.
Movement of Molecules
• Molecules are in constant motion.
• They naturally move from high concentration to
low concentration or you could say that molecules
like to spread out.
High
concentration
Here!
Low
concentration
here
• This type of
movement is called
PASSIVE
TRANSPORT.
• It does NOT require
any energy to move.
• Can you think of a
time you move but
do not require
energy?
Concentration Gradient
• This refers to a gradual change in
concentration from one area to another.
• When you hear this term think of the “hill”
A concentration gradient is what causes
passive transport to occur
3 TYPES OF PASSIVE
TRANSPORT
1. Diffusion: the process by which
molecules spread from areas of high
concentration to areas of low
concentration.
2. Facilitated Diffusion (to “facilitate” means
to help) diffusion helped by channel
proteins
3. Osmosis: movement of water through a
membrane
DIFFUSION
When the molecules are even throughout a
space
- it is called EQUILIBRIUM
• Why is it hard for
people to “sneak” a
cigarette?
• The smoke molecules
move from high
concentration (the
cigarette) to low
concentration
(out into the hallway)
• What about
perfume or
cologne?
Water will move across membrane
until the concentration of ‘free’
water molecules are equal
ISOTONIC SOLUTION
Since the solute
concentration is equal on
the inside and the outside of
the cell, the net movement of
water is equal.
Most cells exist in this type
of environment
How diffusion and osmosis effect cells:
What type of solution is this cell in?----
HYPOTONIC/HYPERTONIC/ISOTONIC?
Water will move into the cell until it
reaches equilibrium
If this happens long enough, an
animal cell explodes. This is called
cytolysis. (lysis means to break)
https://www.youtube.com/watch?v=OYoaLzobQmk
How diffusion and osmosis effect cells:
What type of solution is this cell in?----
HYPOTONIC/HYPERTONIC/ISOTONIC?
Since there are more solutes on the
outside of the cell water will move
out of the cell until it reaches
equilibrium
What happened to the cell wall and the cell membrane?
More Practice
• What type of passive
transport is this?
• Does it require energy?
More Practice
• Look at this one
carefully.
• What type of passive
transport is this?
• What side is hypotonic
and which is
hypertonic?
• Does it require energy?