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MEMBRANE
TRANSPORT
BY
D.SHEEBA
1ST M.SC
BIOCHEMISTRY

2. Introduction:
 It is the transport system by which various molecules
enter into & out of the cell across cell membrane.
Cells have various transport mechanism.
The molecules pass directly through lipid layer or via
membrane channel ,or not the molecules is altered it passes
through membrane.
 The process require energy or not the process require
energy.
 Membrane transport is categorized by 2 major groups.
 Passive transport.
 Active transport.

3. TRANSPORT
Passive transport
 Simple diffusion
 Osmosis
 Facilitated diffusion
Active transport
 Primary active transport
 Secondary active transport

4. PASSIVE TRANSPORT
 It does not require energy to transport
molecules across cell membrane.
Molecules are transported from its
higher conc. to lower conc. gradient .
 It does not work against concentration gradient.

6. i. Simple diffusion:
 Simple diffusion is the transport or movement of
molecules from higher concentration to lower concentration
without expenditure of energy.
 In this process, molecules simply diffuses through the pore of
Cell membrane.
 Simple diffusion do not require transporter protein.
 When the concentration of molecules is different inside and
outside of the cell membrane, concentration gradient is established
 Then the molecules moves from higher concentration to lower
concentration until equilibrium is maintained.

7. When the concentration of molecules becomes equal on both
side of the membrane, transport process stops.
The molecules after entering the cell transform metabolically,
preventing to build up concentration of transported molecules,
hence the concentration gradient remain established.
The rate of diffusion is determined by concentration gradient
and permeability of cytoplasmic membrane
Greater the concentration gradient and permeability of the cell
membrane, greater will be the rate of passive diffusion.
Examples: water or gases enter the bacterial cell by simple
diffusion.

8. ii. Osmosis:
The movement of solvent (water) across membrane in response
to the concentration gradient of solute is known as Osmosis.
Bacterial cytoplasm have generally higher solute concentration
than its surrounding.
There are 3 types of solution based on comparison to the
bacterial cytoplasmic concentration.
In isotonic solution: water move equally in both direction
inside and outside of cell.
In hypertonic solution: water moves out of the cell so that cell
shrinks. The process is known as plasmolysis.
In hypotonic solution: water moves inside the cell so that cell
swells up. The process is known as plasmotysis.

9. iii. Facilitated diffusion:
 The process of facilitated diffusion is similar to simple
diffusion as the molecules flows from higher concentration to
lower concentration but it is different from simple diffusion
because it requires transporter protein for the process.
The transporter protein is known as Permease or Porter or
carrier protein.
The transporter protein are specific , some can transport
multiple compounds.
At first solute molecule binds with the transporter protein and
changes the 3D structure of the transporter protein and this
change in shape allows the solute to carried across the
membrane.

10. 2. Active transport:
It requires transporter protein and continuous supply of cellular
energy for the transport of molecules across concentration gradien
t of the membrane.
It is very important to transport the molecules which are present
in very low concentration in the medium.
In active transport permease or transporter protein
carries the molecules across the membrane and the
energy required to transport is obtained by ATP or Ion gradient.
 Example: The uptake of glucose in the intestine of the human
body and also the uptake of minerals or ions into the root hair
cells of the plants

11. Types of Active transport
There are two types of active transport
 Primary active transport
secondary active transport.
Active transport

12. I. Primary active transport
In this process of transportation, the energy is utilized by the
breakdown of the ATP to transport molecules across the
membrane against a concentration gradient.
All the groups of ATP powered pumps contain one or more
binding sites for the ATP molecules, which are present on the
cytosolic face of the membrane.
Basically, the primary active transport uses external chemical
energy such as the ATP.
 Example: Sodium-potassium pump, the most important pump in
the animal cell.
 In this process of transportation, the sodium ions are moved to
the outside of the cell and potassium ions are moved to the inside
of the cell.

13. Secondary active transport
It is a kind of active transport that uses electrochemical energy.
 It takes place across a biological membrane where a transporter
protein couples the movement of an electrochemical ion (typically
Na+ or H+) down its electrochemical gradient to the upward
movement of another molecule or an ion against a concentration or
electrochemical gradient.
Electrochemical Gradient
 It exists whenever there is a net difference in charges.
 The positive and negative charges of a cell are separated
by a membrane, where the inside of the cell has extra
negative charges than outside.
The membrane potential of a cell is -40 to -80 millivolts.

14. Active Transport in Plants
 Like humans and animals, plants also require transport
systems which are mainly involved in the transport of materials,
such as water, minerals, and necessary nutrients to all parts of
the plant for its survival.
Active transport is a mode of transportation in plants, which
uses stored energy to move the particles against the
concentration gradient. In a plant cell, it takes place in the root
cells by absorbing water and minerals.
Active transport always leads to accumulation of molecules
are ions towards one side of the membrane. This mode of
transportation in plants is carried out by membrane proteins and
transports the substance from the lower concentration to higher
concentration