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Transport across cell membrane

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Transport Across Cell
Membrane
By: Areeba Qamar
Lecturer (Physiology)
Why do Substances Transport..?
• Nutrient supply
• Maintains cells environment
• Helps in exchange of materials
• Who is the barrier for transport across cell??
• The Cell Membrane
Barrier can be….
• Permeable
• Impermeable
• Partially Permeable
• Cell membrane is partially permeable
Transporting substance can be….
• Classified by its nature
• Lipid soluble
• Can pass through the membrane.
• Uncharged or nonpolar molecules (such as O2, CO2,
and fatty acids) are also highly lipid soluble.
• Water soluble
• Charged particles (ions such as Na and K) and polar
molecules (such as glucose and proteins).
• For water-soluble ions less than 0.8 nm in dia, the
protein channels serve as an alternative route.
• Classified by its size
2 Types of Energy
• Passive Energy
• Active Energy
Membrane
Transport
Passive
Simple
Diffusion
Facilitated
Diffusion
Active
Primary
Active
Transport
Secondary
Active
Transport
Cotransport
Countertransport
7
Diffusion
Molecules move
from area of
HIGH to LOW
concentration
8
Diffusion
Diffusion is a
PASSIVE process
no energy is used to make
the molecules move.
Trying to reach
EQUILIBRIUM
Same amount of particles
inside as outside
Factors Influencing the Rate of
Diffusion
• FICK’S LAW OF DIFFUSION
• The magnitude (or steepness) of the concentration
gradient
• The surface area of the membrane across which
diffusion is taking place
• The lipid solubility of the substance
• The molecular weight of the substance
• The distance through which diffusion must take place
• Temperature
10
Two Types of Diffusion
11
Simple Diffusion
Doesn’t require energy
Moves high to low
concentration
Example: Oxygen or water
diffusing into a cell and carbon
dioxide diffusing out.
12
Facilitated Diffusion
Doesn’t require energy
Uses channel proteins to move
high to low concentration
Examples: Glucose or amino
acids moving from blood into a
cell.
13
Carrier / Channel Protein Transporter
• Only ions fit through the narrow channels
• Small polar molecules, glucose and amino acids are
transported across the membrane by carriers
• Channels can be open or closed, but carriers are
always “open for business” (the number and kinds
can be regulated)
• Movement through channels is considerably faster
than carrier-mediated transport
• Carrier mediated transport exhibits
• Specificity
• Saturation
• Competition
17
Osmosis
• Diffusion of water
across a membrane
• Moves from
• HIGH water potential
(low solute)
• to
• LOW water potential
(high solute)
Diffusion across a membrane
Semipermeab
le membrane
18
Osmosis : H2O Across A Membrane
High H2O potential
Low solute concentration
Low H2O potential
High solute concentration
Tonicity
• Refers to the effect, the concentration of nonpenetrating solutes in a solution
has, on cell volume.
• Whether the cell remains the same size,
swells, or shrinks
20
Cell in Isotonic Solution
Equal salt inside and outside the cell
10% NaCL
90% H2O
ENVIRONMENT
CELL
10% NaCL
90% H2O
What is the direction of water
movement?
equilibrium
The cell is at _______________.
NO NET
MOVEMENT
21
Cell in Hypotonic Solution
Less salt outside the cell than inside the cell
10% NaCL
90% H2O
CELL
60% NaCL
40% H2O
What is the direction of water
movement?
22
Cell in Hypertonic Solution
more salt outside the cell than inside the cell
20% NaCL
80% H2O
ENVIRONMENT
CELL
5% NaCL
95% H2O
What is the direction of water
movement?
23
Isotonic Solution
NO NET MOVEMENT
OF H2O (equal
amounts entering &
leaving)
Hypotonic
Solution
CYTOLYSIS
Hypertonic
Solution
PLASMOLYSIS
24
Osmosis in Red Blood Cells
Isotonic
Equilibrium
Hypotonic
Cytolysis
Hypertonic
Plasmolysis
25
ACTIVE TRANSPORT
26
Requires energy or ATP
Moves materials from Low to
High concentration
EXAMPLE: Sodium/Potassium
pump Pumping Na+ out & K+ in
against strong concentration
gradients.
Na/Glucose Co-transport
Vesicular Transport
• Substances which are much too big for channels, and
no carriers exist for them (they would not even fit into
a carrier molecule)
• These large particles are transferred between the ICF
and ECF not by crossing the membrane but by being
wrapped in a membrane-enclosed vesicle, a process
• known as vesicular transport.
• Vesicular transport requires energy expenditure by the
cell, so this is an active method of membrane
transport.
Vesicular
Transport
Endocytosis
Phagocytosis
Exocytosis
Pinocytosis
31
Moving the “Big Stuff”
Large molecules move materials into the cell by one of two
forms of endocytosis.
Phagocytosis
Intake solid material
Pinocytosis
Intake particles suspended
in water
32
Molecules are moved out of the cell by vesicles that
fuse with the plasma membrane.
This is how many hormones are secreted.
33
Exocytosis
Large molecules that are manufactured in the cell are
released through the cell membrane.
Inside Cell
Outside the Cell
Thank You…
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