Cell Transport Mechanisms

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Cell Transport Mechanisms
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Moving molecules across the Cell Membrane
Two methods Passive Transport Active
Transport
Does not expend energy
Does expend energy
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Passive Transport
Allows molecules to move on their own according
to natural laws of physics
Everything tends towards disorder/chaos
Three types of passive transport
mechanisms Diffusion Osmosis Facilitated
diffusion
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Passive Transport Diffusion
Movement of molecules is random When they bump
into each other, they push each other away When
they are highly concentrated, they bump into each
other more often
This forces molecules to move from areas of high
concentration to areas of low concentration
High Concentration
Down a concentration gradient Down the hill
Low Concentration
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Passive Transport Diffusion

Equilibrium
When molecules have reached equal concentrations
in both locations, diffusion ends.
Molecules continue moving, but they move in both
directions equally. NO NET CHANGE.
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Diffusion across a Membrane
Examples small molecules (CO2,O2) small
lipids alcohol
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Passive Transport Osmosis
Moves water molecules across cell membrane (into
or out of cells) Molecules still move down the
concentration gradient
Purple dots are solutes, not water molecules
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Passive Transport Osmosis
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Passive Transport Osmosis
Osmotic Pressure Pressure created by the
presence of water in the cell cell shrinks or
expands
Example Blood cell in low/high salt solutions
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Passive Transport Osmosis
Hypertonic Solution Conc. of solutes outside
cell is higher
Animal Cell
5 salt
2 salt
Plant Cell
Water leaves cell
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Passive Transport Osmosis
Isotonic Solution Conc. of solutes outside cell
is equal to inside cell
Animal Cell
5 salt
5 salt
Plant Cell
Water leaves and enters cell at the same rate NO
NET MOVEMENT
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Passive Transport Osmosis
Hypotonic Solution Conc. of solutes outside cell
is lower
Animal Cell
2 salt
5 salt
Plant Cell
Water enters cell
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Passive Transport Facilitated Diffusion
Molecules still move down the concentration
gradient, but cannot pass phospholipids on their
own.
Rely on proteins imbedded in membrane to help
them across Proteins are specific to the type of
molecule that uses them
Protein Channels
Transport Proteins
Examples water salt ions glucose
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Active Transport
Moves molecules against the concentration
gradient from areas of low concentration to areas
of high concentration.
Restores order
Takes energy to go uphill
ATP
Protein pumps move molecules into or out of cell
against gradient.
Outside Cell
Inside Cell
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Active Transport
Exocytosis Moving molecules out of cells
Endocytosis Moving molecules into
cells Phagocytosis cellular eating Pinocytosi
s cellular drinking
Both processes involve moving large quantities of
materials with the use of vesicles (wrap
materials in membranes).
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Endocytosis
Molecules move into a pocket of the cell
membrane
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Endocytosis
Pocket pinches off the membrane into cytoplasm
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Endocytosis
Vesicle has now formed and can move around inside
cell
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Exocytosis
Vesicle pinches off Golgi Apparatus
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Exocytosis
Free vesicle migrates towards cell membrane
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Exocytosis
Vesicle contacts cell membrane and begins to fuse
with it
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Exocytosis
As vesicle becomes part of plasma membrane,
contents spill out of cell
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Endocytosis and Exocytosis
These two processes occur at roughly the same
rate

No overall change in cells size