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Cell Membrane
Cell Membrane
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-Thin flexible layer around
cell
-Controls what goes in or out
of cell
-Provides protection and
support
-Made of a phospholipid
bilayer—two layers of lipids
-Proteins are embedded in
bilayer
-These help move materials
across the cell membrane
Phospholipids in cell membrane are
arranged in two layers with nonpolar
fatty acid “tails” together. The polar
“heads” face the watery environments
found inside and outside the cell.
 This structure
creates a barrier
that helps the cell
maintain homeostasis
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Cell Membrane Clip
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http://www.youtube.com/watch?v=G
W0lqf4Fqpg
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The cell membrane can be described as a
Fluid Mosaic Model.
– The phospholipids in the bilayer float
together like beach-balls on water. The lipids
are in constant motion, and can slide past
each other, and other molecules, like
proteins can move in between them.
Figure 7-12 The Structure of the
Cell Membrane
Section 7-3
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
Movement across Cell Boundaries
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Passive Transport
Does not require energy
Materials move from area of high
concentration to area of low
concentration until equilibrium * is
reached
Three types of passive transport
1.
Diffusion is the movement of particles
from where they are more concentrated*
to where they are less concentrated.
It occurs due to the random movement of
particles.
It continues until a dynamic equilibrium is
reached—the concentration is the same on
both sides of the membrane.
Particles still move in both directions across
membrane, but there is no further change
in concentration.
2. Osmosis is the movement of water through a
selectively permeable membrane.
This means that some substances can pass
through the membrane, and others can’t due to
their size or charge.
Isotonic: concentrations of the water are the same
both inside and outside the cell; water enters and
leaves cell at same rate; cell size doesn’t change
Hypotonic: lower water concentration inside the
cell than outside; water enters the cell; cell swells
Hypertonic: lower water concentration outside the
cell than inside; water moves out of the cell; cell
shrinks
3. Facilitated Diffusion is when large
molecules like glucose move across the cell
membrane through protein channels:
protein molecules embedded in the lipid
bilayer.
They are specific to different substances
and have carbohydrate marker chains on
them that act as identification cards.
The protein channels act like an open gate
for the substance they are marked for.
Section 7-3
Protein
channel
Passive Transport Clip
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http://www.youtube.com/watch?v=2U
PqLm-uDnI
Figure 7-12 The Structure of the
Cell Membrane
Section 7-3
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
Active Transport
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Requires energy from the cell
Materials move from an area of lower
concentration to an area of higher
concentration.
It is usually done by transport proteins
or “pumps” found in the cell
membrane
Three types of active transport
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Sodium/Potassium
Pump
In animal cell
membranes
Uses energy to
move Na+ out of cell
and K+ into cell
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Endocytosis:
Process of moving large molecules into a
cell
Materials enter the cell by making folds in
the cell membrane.
Requires energy
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Exocytosis:
Process of moving
large materials out
of the cell.
Materials leave the
cell by fusing
vesicles with the
cell membrane.
Requires energy
Video CLip
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http://www.youtube.com/watch?v=W
6rnhiMxtKU