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Mechanism of Transportation
in a cell
Or
Transportation of molecules in a cell
Presentation by: Mahendra Kandel
Email: [email protected]
For: Bachelor of Pharmacy, NIST
Date: December 31, 2012
presentation by: Mahendra Kandel
1
Functions of Cell Membrane
1. Protect cell
2. Control incoming and outgoing
substances
3. Maintain ion concentrations of various
substances
4. Selectively permeable - allows some
molecules in, others are kept out
presentation by: Mahendra Kandel
2
Phospholipid Bilayer
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3
Structure of the Cell Membrane
Outside of cell
Carbohydrate
chains
Proteins
Lipid
Bilayer
Transport
Protein
Phospholipids
Inside of cell
(cytoplasm)
Go to
Section:
presentation by: Mahendra Kandel
4
The Selectively Permeable
Nature
of Cell Membranes
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5
Membrane Proteins
• Each type of protein in a membrane has a
special function
– Adhesion proteins – hold to surface, cells
– Receptor proteins – receive messages
– Enzymes – speed up reactions
– Transport proteins (active and passive)
active – require energy to transport
passive – no energy required for transport
presentation by: Mahendra Kandel
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Concentration and Gradients
• Concentration
– The number of molecules (or ions) of
substance per unit volume of fluid
• Concentration gradient
– The difference in concentration between two
adjacent regions
– Molecules always move from a region of higher
concentrationpresentation
to one
of lower concentration 7
by: Mahendra Kandel
Types of Transportation
• Passive Transport
• Active Transport
• Endocytosis
(phagocytosis & pinocytosis)
• Exocytosis
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Passive Transport
• No energy required
• Move due to gradient
– differences in concentration, pressure, charge
• Move to equalize gradient
– High moves toward low
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Passive Transportation
Weeee!!!
high
low
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Types of Passive Transport
1. Diffusion
2. Osmosis
3. Facilitated diffusion
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Diffusion
• Movement of molecules from an area
of high concentration to an area of
low concentration.
• Movement from one side of a
membrane to another, un-facilitated
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Diffusion
• Molecules move to equalize concentration
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Diffusion
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Osmosis
• Special form of diffusion
• Fluid flows from lower solute concentration
• Often involves movement of water
– Into cell
– Out of cell
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Osmosis
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Tonicity is a relative term
• Hypotonic Solution - One solution
has a lower concentration of solute
than another.
• Hypertonic Solution - one solution
has a higher concentration of solute
than another.
• Isotonic Solution - both solutions
have same concentrations of solute.
presentation by: Mahendra Kandel
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Solution Differences in a
tissue/cells
• solvent + solute = solution
• Hypertonic
– Solutes in cell more than outside
– Outside solvent will flow into cell
• Isotonic
– Solutes equal inside & out of cell
• Hypotonic
– Solutes less than outside cell
– Fluid will flow out of cell
presentation by: Mahendra Kandel
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Facilitated Diffusion
• Differentially permeable membrane
• Channels (are specific) help molecule
or ions enter or leave the cell
• Channels usually are transport proteins
• No energy is used
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Types of Transport
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Process of Facilitated Transport
• Protein binds with molecule
• Shape of protein changes
• Molecule moves across membrane
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Active Transport
• Molecular
movement
• Requires
energy (against
gradient)
• Example is
protein pump
This is gonna
be hard
work!!
high
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low
23
1. Protein Pumps -transport proteins that
require energy to do work
• Example: Sodium / Potassium Pumps
are important in nerve responses.
presentation by: Mahendra Kandel
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• Active
transport in
two solutes
across a
membrane
• Na+/K+
pump
• Protein
shape
change
FLUID
OUTSIDE
CELL
Transport
protein
First
solute
1
First solute,
inside cell,
binds to protein
2
ATP transfers
phosphate to
protein
3
Protein releases
solute outside
cell
6
Protein releases
second solute
25
into cell
Second
solute
Phosphate
detaches from
presentation by: Mahendra Kandel
protein
4
Figure 5.18
Phosphorylated
transport protein
Second solute
binds to protein
5
Sodium-Potassium Pump
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Endocytosis
• Movement of large material
– Particles
– Organisms
– Large molecules
• Movement is into cells
• Types of endocytosis
– bulk-phase (nonspecific)
– receptor-mediated (specific)
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Bulk-phase endocytosis
Extracellular fluid is captured in a
vesicle and brought into the cell; the
reverse of exocytosis
• Receptor-mediated endocytosis
– Specific molecules bind to surface receptors,
which are then enclosed in an endocytic
vesicle
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Process of Endocytosis
• Plasma membrane surrounds material
• Edges of membrane meet
• Membranes fuse to form vesicle
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Forms of Endocytosis
• Phagocytosis – cell eating
• Pinocytosis – cell drinking
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Exocytosis
• Reverse of endocytosis
• Cell discharges material
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Exocytosis
• Vesicle moves to cell surface
• Membrane of vesicle fuses
• Materials expelled
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Summary of Methods of Transport
Across Membranes
1. Diffusion -passive transport - no energy
expended
2. Osmosis - Passive transport of water
across membrane
3. Facilitated Diffusion - Use of proteins to
carry polar molecules or ions across
4. Active Transport- requires energy to
transport molecules against a concentration
gradient – energy is in the form of ATP
presentation by: Mahendra Kandel
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• Thank you!
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