Membrane Transport
Cell or Plasma Membrane
• Composed of double layer of phospholipids
•
•
•
and proteins (phospholipid bilayer)
Surrounds outside of ALL cells
Controls what enters or leaves the cell
Living layer
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
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Lipid bilayer
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Phospholipids
• Heads contain glycerol &
•
•
•
phosphate and are hydrophilic
(attract water)
Tails are made of fatty acids and
are hydrophobic (repel water)
Make up a bilayer where tails
point inward toward each other
Can move laterally to allow
small molecules (O2, CO2, & H2O
to enter)
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Cell Membrane Proteins
• 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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The Cell Membrane is also
referred to as the Fluid
Mosaic Model
Molecules in cell membranes are
constantly moving
and changing
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Structures Of The Plasma Membrane
• Phosphate Head: Made of a phosphate group (polar and
•
•
•
•
attracts water)
Carbohydrate: Used for cell recognition
Membrane Protein: Transports large particles across the cell
membrane
Cholesteral: Helps stabilize the phospholipids
Lipid Tails: Made of fatty acids (non-polar and does not attract
water)
Diffusion
• Movement of particles
– From high
– To Low
Diffusion
• Concentration: the mass of solute (what's being
•
dissolved) in a given volume of solvent (what’s doing
the dissolving)
Equilibrium: the concentration throughout a
solution is the same
Diffusion
• ● Concentration gradient: the difference in
•
concentration across a barrier/membrane
● Because diffusion depends upon random particle
movements, substances diffuse across membranes
without requiring the cell to use energy
Osmosis
• Movement of water
• From high
to low
• Across a
selectively
permeable
membrane
-selects what moves
in and out
Osmosis
Dynamic Equilibrium
• Equal
concentrations are
reached
– Not the same
volumes
• Continued
•
movement across
the membrane
Not gain or loss
Osmosis
• ● Osmosis is the diffusion of water through a
selectively permeable barrier. Water will tend to
move across the membrane until equilibrium is
reached, when this occurs the two solutions will
be isotonic, the same.
• ● When a solution is more concentrated with
solute it is said to be hypertonic, whereas a
dilute (less concentrated) solution is said to be
hypotonic.
Osmosis
Isotonic Solutions
• Iso- equal
• No change in concentrations
– Water still moves
– Same amount of water moves in as moves out
• Both sides of membrane are the same
Hypertonic Solution
• Hyper- Over
• Out side of cell
– More dissolved substance
– Less water
• Water moves out of cell
Hypotonic Solution
• Hypo- under
• Out side of cell
– Less dissolved substance
– More water
• Water moves into cell
Passive Transport
• Cell uses no energy
• From high to low
Plasma
membrane
Concentration
gradient
Facilitated Diffusion
• Type of passive
•
transport
Use transport
proteins
– Channel proteins
– Carrier proteins
• Changes shape
• From high to low
Facilitated Diffusion
• ● During facilitated diffusion molecules that
would not normally be able to cross through
the membrane, such as glucose, diffuse
across the membrane through selected
protein channels.
• It is dependent upon the concentration
gradient because it does not require the cell
to expend any energy.
Active Transport
• Cell uses energy
• Against concentration
gradient
– From low to high
• Carrier Proteins
– Molecule binds with carrier
protein
– Energy then used to
change shape
– Molecule released on other
side
– Carrier protein returns to
original shape
Active Transport
• ●The movement of material across a membrane and
•
against a concentration gradient is called active
transport.
Like facilitated diffusion this is carried out by protein
channels in the membrane called transport proteins,
however in this form of diffusion energy is expended in
the process of “pumping” the material “uphill” against
the gradient.
Active Transport
Molecule to
be carried
Energy
Molecule
being carried
Large Particle Transport
• ● Endocytosis is the process of taking material
•
into the cell by means of enfolding's, or pockets,
of the cell membrane. The pocket or enfold,
once it has surrounded the molecule, then closes
and breaks off from the membrane forming a
vacuole. Two examples of endocytosis are
phagocytosis (cell eating) and pinocytosis
(cell drinking).
● Exocytosis works the opposite of
endocytosis. It is a vacuole with material
designated to leave the cell which joins with the
cell membrane then releases its material outside
of the cell.
Large Particle Transport
(Exocytosis and Endocytosis)
Large Particle Transport
• Not through
•
•
membrane
Requires energy
Exocytosis- out
Large Particle Transport
• Endocytosis- in
Types of Endocytosis
Pinocytosis: liquid (into)
Phagocytosis: Solid (into)