1. TRANSPORT ACROSS
MEMBRANES (BCH 857)
ALUKO, Adeola
ADESEJI, Wasiu
AROGUNDADE,
Tolulope
GBADAMOSI, Ismail
Course Lecturer: Dr.
ARIISE
2. OUTLINE
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Introduction
The Cell Membrane
Types of Transport
Tonicity of Solutions
Diffusion
Facilitated Transport
Osmosis
Active Transport
Factors Affecting Transport Across a Membrane
Endocytosis and Exocytosis
Summary and Conclusion
4. THE CELL MEMBRANE
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Comprises phospholipids and
proteins in ratio 3:2;
Contains carbohydrate bound to
protein as glycoprotein;
Measures about 6.5-10nm in
thickness;
Has glycolipids and glycoprotein
projecting outwards as glycocalyx;
Contains pores measuring between
0.7-1.0μ in diameter;
Is selectively permeable.
6. 6
PASSIVE
ACTIVE
Passive diffusion is a spontaneous phenomenon that
increases the entropy of a system and decreases the free
energy. The transport process is influenced by the
characteristics of the transport substance and the nature
of the bilayer.
In active transport a solute is moved against a
concentration or electrochemical gradient, in doing so
the transport proteins involved consume metabolic
energy, usually ATP.
TYPES OF TRANSPORT
7. TRANSPORT PROTEINS
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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.
8. TONICITY OF SOLUTIONS
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The tonicity of a solution will affect the size & shape of cells:
ISOTONIC SOLUTION:
the solution concentration is equal on both sides of the membrane.
HYPERTONIC SOLUTION:
The solution outside the cell is more concentrated than inside.
HYPOTONIC SOLUTION:
The concentration inside the cell is more concentrated than outside.
12. DIFFUSION
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Molecules diffuse until
they are evenly
distributed.
EXAMPLES of molecules that
easily cross cell membranes by
simple diffusion are: oxygen,
carbon dioxide, alcohols, fatty
acids, glycerol, and urea.
13. FACILITATED TRANSPORT
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Molecules will randomly
move through the opening
like pore, by diffusion.
This requires no energy, it
is a PASSIVE process.
Molecules move from an
area of high concentration
to an area of low conc.
14. FACILITATED TRANSPORT
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Each protein
channel or protein
carrier will allow
only ONE TYPE OF
MOLECULE to pass
through it.
Many channels contain a
“gate” which control the
channel's permeability.
15. OSMOSIS
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Diffusion of water across a
membrane.
Moves from HIGH water potential
(low solute) to LOW water potential
(high solute).
16. OSMOSIS
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•To cross the membrane, water
must move through a protein ion
channel.
•In certain cellular conditions,
these protein channels can be
opened or closed (i.e. in the
kidneys, large intestines)
depending on how much water is
needed by the body.
17. ACTIVE TRANSPORT
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Molecules move against the concentration
gradient.
Requiresenergy
1. Solute Pumps (Na+-K+-ATPase pump)
mostly in nerve membranes.
2. Bulk Transport.
18. FACTORS AFFECTING MOVEMENT ACROSS MEMBRANES
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The rate of diffusion will be increased when there is :
1. Concentration: the difference in concentration between two areas (the
concentration-gradient) causes diffusion. The greater the difference in
concentration, the faster the diffusion.
2. Molecular size: smaller substances diffuse more quickly. Large
molecules (such as starches and proteins) simply cannot diffuse
through.
3. Shape of Ion/Molecule: a substance’s shape may prevent it from
diffusing rapidly, where others may have a shape that aids their
diffusion.
19. FACTORS AFFECTING MOVEMENT ACROSS MEMBRANES
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4. Viscosity of the Medium: the lower the viscosity, the more slowly molecules
can move through it.
5. Movement of the Medium: currents will aid diffusion. Like the wind in air,
cytoplasmic steaming (constant movement of the cytoplasm) will aid
diffusion in the cell.
6. Solubility: lipid - soluble molecules will dissolve through the phospholipid
bilayer easily, as will gases like CO2 and O2.
7. Polarity: water will diffuse, but because of its polarity, it will not pass
through the non-polar phospholipids. Instead, water passes though
specialized protein ion channels.
The cell membrane (or plasma membrane or plasmalemma) surrounds the cytoplasm of living cells, physically separating the intracellular components from the extracellular environment.
Permeable- ability to pass through a membrane
Impermeable- can’t pass through
Selectively Permeable (semipermeable)- some things can pass through and some can’t
The cell membrane is selectively permeable and able to regulate what enters and exits the cell, thus facilitating the transport of materials needed for survival.
The cell membrane thus works as a selective filter that allows only certain things to come inside or go outside the cell. The cell employs a number of transport mechanisms that involve biological membranes:
The movement of substances across the membrane can be either "passive", occurring without the input of cellular energy, or "active", requiring the cell to expend energy in transporting it.
A transport protein (variously referred to as a transmembrane pump, transporter protein, escort protein, acid transport protein, cation transport protein, or anion transport protein) is a protein that serves the function of moving other materials within an organism. Transport proteins are vital to the growth and life of all living things. There are several different kinds of transport proteins.
Some molecules are not normally able to pass through the lipid membrane, and need channel or carrier proteins to help them move across.
This does not require energy when moving from [H] to [L] (with the concentration gradient).
Molecules that need help to move through the plasma membrane are either charged, polar, or too large.
When the gate is open, the channel transports, and when the gate is closed, the channel is closed.
These gates are extremely important in the nerve cells
EXAMPLES of molecules that move this way are all of the things that require protein carriers to move across the plasma membrane.
ions (like Na+ and K+ in cells, and iodine) and sugars, amino acids, nucleotides...
Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails.
Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails.
Just like the whole organism needs some substances taken in to survive, so do cells too…
Everything that is transported across the cell membrane takes place by one of two fundamental processes.
