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Transportation of Materials Across the Cell Membrane
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Composed of double layer of phospholipids and proteins
Controls what enters or leaves the cell
Surrounds outside of ALL cells
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
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The cell membranes of all cells are selectively permeable
This means that some materials can pass easily through
the membrane
Examples: H20, CO2 and O2
This also means that some materials cannot pass easily
through the membrane
Examples: glucose and salts
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Proteins help move large molecules or aid in cell recognition
Peripheral proteins are attached on the surface (inner or
outer)
Integral proteins are embedded completely through the
membrane
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Provide a binding site for enzymes
Interlocking surfaces bind cells together (junctions)
Contains the cytoplasm (fluid in cell)
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Phospholipid bilayer makes up the cell membrane
 Contains a polar head (attracts H2O) and 2 non-polar fatty
acid tails (repels H2O)
How is a phospholipid different from a triglyceride?
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Fluid: individual phospholipids and proteins can move side-toside within the layer, like a liquid.
Mosaic: the pattern produced by the scattered proteins on the
surface of the cell when the membrane is viewed from above.
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Materials that are soluble in lipids can pass through the cell
membrane easily
Ex: Oxygen, carbon dioxide, and water
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Passive Transport
 Does not require
cellular energy
 Types:
1. Simple
Diffusion
2. Osmosis
3. Facilitated
Diffusion
Active Transport
 Does require
cellular energy
 Types:
1. Membrane
Pumps
2. Endocytosis
3. Exocytosis
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 Movement
of materials from a region of high
concentration to a region of low concentration
 Materials are moving down/with
their concentration gradient
 Example:
Oxygen diffusing
into a cell and carbon dioxide
diffusing out using kinetic
energy
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Osmosis is the passive transport (diffusion) of water across
a membrane
Moves from a region of HIGH water potential (low solute) to
a region of LOW water potential (high solute)
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The purpose of osmosis is to
balance out the concentration of
materials between the
environment inside of the cell and
the environment outside the cell
Water moves because the other
materials cannot
This allows the cell to be in
equilibrium - balance
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1.
2.
3.
Solution - a liquid mixture in which the minor component
(the solute) is uniformly distributed within the major
component (the solvent).
Examples – salt water or glucose solutions; solutes are salt
or glucose, solvent is water
Types of solutions:
Isotonic
Hypotonic
Hypertonic
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10% NaCL
90% H2O
ENVIRONMENT
CELL
10% NaCL
90% H2O
Q: What is the direction of water movement
in an isotonic solution?
A: No net movement (water molecules moving equally back and forth)
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10% NaCL
90% H2O
ENVIRONMENT
CELL
20% NaCL
80% H2O
Q: What is the direction of water movement
in a hypotonic solution?
A: Water moves into the cell
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15% NaCL
85% H2O
ENVIRONMENT
CELL
5% NaCL
95% H2O
Q: What is the direction of water movement
in a hypertonic solution?
A: Water moves out of the cell.
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Hypotonic solution will result in
cytolysis – cell bursts from build up
of water inside cell
Hypertonic solution will result in
plasmolysis – cell membrane pulls
away from the cell wall in plant,
fungal or bacterial cells
Plant cells prefer a hypotonic
environment
Animal cells prefer an isotonic
environment
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Uses transport
proteins to move
materials from high to
low concentration
Examples: Glucose or
amino acids moving
from blood stream into
a cell.
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Types of Membrane Proteins:
Structural
Cell recognition
Communication
Transport:
a.
b.
Channel proteins are embedded in the cell membrane & have
a pore for materials to cross
Carrier proteins can change shape to move material from
one side of the membrane to the other
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Channel proteins act
as bridges to allow
materials to pass
across
the membrane
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Some Carrier proteins
do not extend through
the membrane.
They bond and drag
molecules through the
lipid bilayer
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Cells need a steady supply of sodium (Na+), potassium (K+),
calcium (Ca2+) and hydrogen (H+) in order to function
correctly
Protein pumps that span the cell membrane are powered by
ATP and supply these materials to the cell on demand
This requires a steady supply of ATP
Materials are moving from and area of low concentration to
an area of high concentration
They are moving up/against their concentration gradient
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3 Na+ pumped out for every 2 K+ pumped in
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Q: What is a vesicle?
A: A small bubble within a cell surrounded in its own lipid
bilayer.
Q: What is the function of a vesicle?
A: Vesicles are involved in:
• Metabolism
• Transport of materials
• Enzyme storage
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Types of active transport using vesicles:
• Exocytosis
• Endocytosis
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Exocytosis -using a vesicle to move big stuff out
of the cell
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How it works:
Vesicle is formed around some sort of material made by
the cell (like proteins or hormones)
Vesicle is released and travels toward cell membrane
Vesicle fuses with cell membrane
Vesicle expels materials to the outside of the cell
membrane
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Large amount of materials move into the cell by one
of two forms of endocytosis:
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Pinocytosis  Materials dissolve in water to be brought into cell
 Called “Cell Drinking”
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Phagocytosis - Used to engulf large particles such as food,
bacteria, etc. into vesicles.
 Called “Cell Eating”
 White blood cells eat foreign substances in your body this way
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Pinocytosis
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