Transport across cell membrane

TRANSPORT ACROSS CELL
MEMBRANE
Name :Y.Vamsi Krishna
Reg No :17BCB0054
3/11/2018Y.Vamsi Krishna 17BCB0054
1

CELL MEMBRANE
1.All cells have a cell membrane
2. Functions:
a.Controls what enters and exits the cell to
maintain an internal balance called homeostasisb.
Provides protection
2

FUNCTIONS OF CELL MEMBRANE:
 Protective Function
 Selective permeability
 Absorptive function
 Excretory function
 Exchange of gases
 Maintenance of shape and size of the
cell
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TRANSPORT – WHAT IT MEANS?
 Its highly selective filter, Its highly selective filter,
permits nutrients and permits nutrients and leaves the
waste products leaves the waste products from the cell.
from the cell.
 Maintain Homeostasis. Maintain Homeostasis.
 Makes Cytosol Makes Cytosol environment to different
environment to different
 Play an important role in Play an important role in cell
to cell communication. cell to cell communication.
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TRANSPORT MECHANISMS
Active process
 Primary Transport
 Secondary Transport
Passive process
 Simple diffusion Simple diffusion
 Facilitated diffusion Facilitated
diffusion
 Osmosis Osmosis
 Bulk flow Bulk flow
 Filtration
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PASSIVE TRANSPORT
cell doesn’t use energy
1. Diffusion
2. Facilitated Diffusion
3.Osmosis
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7

FACTORS THAT INFLUENCE DIFFUSION
RATES
 Distance –
The shorter the distance, the more quickly [ ] gradients are eliminated
Few cells are father than 125 microns from a blood vessel
 Molecular Size
Ions and small molecules diffuse more rapidly
 Temperature –
↑ temp., ↑ motion of particles
 Steepness of concentrated gradient –
The larger the [ ] gradient, the faster diffusion proceeds
 Membrane surface area –
The larger the area,the faster diffusion proceeds
8

DIFFUSION ACROSS MEMBRANES
Simple Diffusion
 Lipophilic substances can enter cells
easily because they diffuse through the
lipid portion of the membrane
 Examples are fatty acids, steroids,
alcohol, oxygen, carbon dioxide, and
urea,
Channel-Mediated Diffusion
 Membrane channels are
transmembrane proteins .Only 0.8 nm
in diameter
 Used by ions, very small water-soluble
compounds
 Much more complex than simple
diffusion
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DIFFUSION THROUGH THE PLASMA
MEMBRANE
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OSMOSIS
Osmosis is the process of moving water
across a semi permeable membrane
towards ion or solut
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OSMOSIS AND CELLS
 Important because large volume changes caused by water movement
disrupt normal cell function
 Cell shrinkage or swelling
Isotonic: cell neither shrinks nor swells
Hypertonic: cell shrinks (crenation)
Hypotonic: cell swells (lysis)
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ACTIVE TRANSPORT
cell does use energy
1. Endocytosis
2. Exocytosis
3. Protein Pumps
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WHAT IS ACTIVE TRANSPORT ?
 Active transport is the Active transport is the transport
of substances from transport of substances from a
region of lower a region of lower concentration to
higher concentration to higher concentration using
energy, concentration using energy, usually in the form
of usually in the form of ATP ATP. .
 Examples: Na, K and Ca Examples: Na, K and Ca active
transport. active transport.
 1.sodium-potassium pump
 2.Calcium pump
 3.Potassium hydrogen pump
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ACTIVE TRANSPORT NEEDED FOR
1. Maintaining the 1. Maintaining the
Chemical and Electrical Chemical and
Electrical Charge at rest. Charge at rest.
2. Intake of Substances through gated
Channels.
3. Collecting of ions with more
concentration
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ACTIVE TRANSPORT - WHY ?
Cells cannot rely solely on passive
movement of substances across their
membranes.
In many instances, it is necessary to
move substances against their electrical
or chemical gradient to maintain the
appropriate concentrations inside of
the cell or organelle.
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PUMPS INVOLVED IN ACTIVE TRANSPORT
1.Sodium-potassium pump Found in
many cells
2.Calcium pump Found in membrane
of Sarcoplasmic reticulum
3.Potassium hydrogen pump Found
in Gastrointestine cell membrane
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SECONDARY ACTIVE TRANSPORT
The transport of substances against a concentration gradient involving
energy to establish a gradient across the cell membrane, utilizes the
gradient to transport a molecule of interest up its concentration
gradient .
THE TRANSPORT MAY BE
In the same direction (SYMPORT)
In the opposite direction (ANTIPORT)
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MECHANISMS OF SECONDARY ACTIVE TRANSPORT
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CARRIERS TYPE PROCESSES
Carriers are transport proteins that binds ions and other molecules and
then change their configuration moving the bound molecules from one
side of cell membrane to the other.
 Types of carriers :
1.Uniporters
2.Symporters
3.Antiporters
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UNIPORT
The movement of a single Substance.
 It requires no energy from the cell.
 Examples.
Simple diffusion.
Facilitated diffusion.
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MECHANISM OF UNIPORT
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SYMPORT (CO-TRANSPORT)
Transport of two substances using the
energy produced by concentration
difference developed by primary active
transport
 Substances are moving in the same
direction.
 Example: transport of amino acids,
Glucose,
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MECHANISM OF CO-TRANSPORT
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ANTIPORT (COUNTER-TRANSPORT)
In this process, the two
substances move across the
membrane in opposite
directions.
Example: Exchange of H+
and Na+ in Renal tubule.
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MECHANISM OF COUNTER-TRANSPORT
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VESICULAR TRANSPORT
1.Endocytosis 2.Exocytosis
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ENDOCYTOSIS
 It is a process by which the large number of particles
are taken with forming the vesicle into the cell
 It is classified into:
 1. Phagocytosis
It is a process by which the large number of particles
are engulfed into the cell.
 2. Pinocytosis
It is a process by which the large number of particles
which are soluble in water are taken into the cell
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EXOCYTOSIS
Exocytosis is a process in which an intracellular vesicle
(membrane bounded sphere) moves to the plasma
membrane and fused the substance into the Extra cellular
fluids For example a few of the processes that use Exocytosis
are:
1. Secretion of proteins like enzymes and antibodies from
cells.
2. Release of neurotransmitter from presynaptic neurons
3. Arosome reaction during fertilization
4. Recycling of plasma membrane
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BULK TRANSPORT
The movement of large number of ions, molecules or
particles that are dissolved or carried in a medium such
as a fluid or air is called bulk flow.
Rate of Bulk transport is determined by the differences in
hydrostatic pressure or air pressure.
Eg: 1. Flow of blood within the vessels.
2.Movement of air into and out of the lungs.
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Active transport
Energy is utilised
Movement of ions takes
place against conc. gradient
Specific carrier is required
Cellular respiratory rate is
high
Enzymes are involved
Passive transport
No Energy is utilised
Movement of ions takes
place favouring conc.
gradient
No carrier is required
No change
No Enzymes are involved
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Transport across cell membrane

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