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The Plasma (Cell) Membrane
The Fluid Mosaic Model
TEM view of the
Plasma Membrane
Function of the Plasma Membrane
• A “selectively” or “semi” permeable
membrane that restricts the
movement of various molecules
into and out of the cell.
• Allows for communication between
cells.
• Provides the cell with a specific
“marker” that tells all of the other
cells who it is.
Membrane Composition
1.
Phospholipid molecules:
* make up most of the cell
membrane
* provides a barrier between
cytoplasm & outside the cell
2.
Carrier proteins:
* used to move molecules across the
membrane
* some require energy others do not
3.
Glycoproteins/ Glycolipids:
* used as cell markers
Phospholipids
• Hydrophilic (loves H2O )
head represents the
PHOSPHO part of the
molecule.
• Hydrophobic (hates H2O )
tail represents the LIPID part
of the molecule.
• Outside & inside the cell
there’s a lot of H2O ,
therefore the hydrophilic
part is in contact with
H2O but the hydrophobic
part is as far away as
possible from H2O.
Carrier Protein
• Passive Channel:
*Leakage channel
*Requires no cellular energy
• Active Channel:
* Open and close to let larger molecules through
* Uses Cellular energy (ATP)
• Channel Protein
Cell Membrane
Glycoproteins
Inside of cell
(cytoplasm)
Protein
channel
Phospholipid
Bilayer
Plasma (Cell) Membrane
• Animation # 1
• Animation # 2
• Animation # 3
Cellular Traffic Worksheet
• #1-4
Moving Materials Across The Cell
Membrane
Two ways :
1. Passive Transport (PT)
Requires no cellular energy
2. Active Transport (AT)
Requires cellular energy (ATP)
Particle Theory
• 1. All matter is made of particles
• 2. The particles are in constant motion
(Kinetic motion of particles)
• 3. The closer the particles are together,
the greater the attractiveness between
them.
Particle Theory
• Solids: definite shape and volume
• Liquids: definite volume but indefinite
shape
• Gases: indefinite shape and volume
• Matter
Three Types of Passive Transport
1. Diffusion
2. Osmosis
3. Facilitated Diffusion
Diffusion
• Molecules move from an area of high
concentration [ ] to an area of low [ ] until
Equilibrium is reached where [ ] levels are
equal.
Diffusion
• Small molecules like O2 and CO2 can diffuse
across the plasma membrane. Large
molecules (ex. Glucose) or ions (an ion is a
charged particle) can’t pass through by
diffusion.
Cellular Traffic Worksheet
• #5-7
Osmosis
• Special type of diffusion involving water
passing through a selectively permeable
membrane.
• Water always move from an area of high [ ]
to an area of low [ ].
How Osmosis Works
Dilute sugar
solution
(Water more
concentrated)
Concentrated
sugar solution
(Water less
concentrated)
Sugar
molecules
Selectively
permeable
membrane
Movement of
water
Osmosis & Cellular Environments
Hypotonic :water [ ] outside cell is greater than
water [ ] inside cell.
Hypertonic: water [ ] outside is less than water
[ ] inside.
Isotonic: water [ ] outside equals water [ ]
inside.
Animal Cell
Hypotonic Solution
high H2O [ ] outside ,
H2O flows into cell ,
pressure builds up ,
cell bursts which is
called cytolysis.
Animal Cell
Hypertonic Solution
low H2O [ ] outside ,
H2O flows out of cell
pressure drops , cell
becomes
dehydrated and
shrivels up.
Animal Cell
Isotonic Solution
The H2O [ ] outside
the cell equals the
H2O [ ] inside the
cell. NO change in
cell. H2O moves in
and out at the same
rate.
Another look:
Plant Cell
Hypotonic Solution
high H2O [ ] outside
the cell , H2O flows
in , pressure builds
up , cytoplasm
pushes against cell
membrane & wall.
This pressure is
Turgor Pressure.
The cell looks stiff
or Turgid.
Plant Cell
Hypertonic Solution
low H2O [ ] outside
cell , H2O flows out ,
pressure drops,
plasma membrane
may collapse which
is called
plasmolysis. The
cell is referred to as
being wilted or
flaccid.
Plant Cell
Isotonic Solution
The H2O [ ] outside
the cell equals the
H2O [ ] inside the
cell. NO change in
the cell. H2O moves
inside & outside at
the same rate.
Another look:
Cellular Traffic Worksheet
• #8-11
Facilitated Diffusion
• Form of PT (no ATP)
• Uses Passive Channel Proteins in cell
membrane to transport large molecules or
ions across cell membrane.
• These channel proteins act as ports ,
shielding these molecules from the cell
membrane.
• Still moving from an area of high [ ] to an
area of low [ ].
Glucose
molecules
Protein
channel
Cellular Traffic Worksheet
• #12-13
Active Transport (AT)
• AT requires ATP to move materials across the
cell membrane against the [ ] gradient.
• 3 Types of AT :
1. Endocytosis
2. Exocytosis
3. Active Channel Proteins
Endocytosis
• A cell extends its plasma
membrane around very
large items and engulfs
them , moving from an area
of decreased [ ] to an area of
increased [ ].
• 2 Types :
1. Pinocytosis
(small particles &
liquid)
2. Phagocytosis
(large particles)
Pinocytosis
Exocytosis
• Excreting materials from a cell packaged in
vesicles.
• The cell uses ATP energy.
Active Channel Proteins
• Proteins or “pumps” in the cell membrane bind to
small molecules or ions and by changing shape
move molecules from an area of low [ ] to high [ ] .
• Movement against the Concentration Gradient
• Particles are drawn against the concentration
gradient using active channels that open and close
using cellular energy ATP
• L to H
• L-H
Homeostasis
• All these examples of cellular traffic are
designed to help the cell maintain a state of
balance between the inside and the outside
of the cell.
Cellular Traffic Worksheet
• #14-18
Test Yourself
• #19-22