A biological membrane or biomembrane is an enclosing or separating membrane that acts as a selectively permeable barrier within living things.

1. Biological Membranes And
Transport
Archana Soni...archi22ss@gmail.com

2. • The plasma membrane is an envelop
surrounding the cell.
• It separates and protect the cell from the
external environment.
• Plasma membrane also provide a connecting
system between the cell and its environment .

3. Detailed structure of the plasma membrane

4. • Chemical composition
• The membranes are composed of lipids, protein
and carbohydrates.
• The actual composition differ from tissue to
tissue.
• Among the lipids, amphipathic lipids
(containing hydrophobic and hydrophilic
groups) namely phospholipids, glycolipids and
cholesterol are found in animal membranes.
• Many animal cell membranes have thick coating
of complex polysaccharides referred to as
glycocalyx.

5. Membrane is a collage of proteins & other molecules
embedded in the fluid matrix of the lipid bilayer
Extracellular fluid
Cholesterol
Cytoplasm
Glycolipid
Transmembrane
proteins
Filaments of
cytoskeleton
Peripheral
protein
Glycoprotein
Phospholipids

6. • Structure of membranes
• Fluid mosaic model proposed by Singer and
Nicolson is a more recent and acceptable model
for membrane structure.
• The biological membrane usually have a
thickness of 5 – 8 nm.
• A membrane is essentially composed of a lipid
bilayer.
• The hydrophobic (nonpolar) region of the lipids
face each other at core of the bilayer while the
hydrophilic (polar) region face outward.

7. More than lipids…
• In 1972, S.J. Singer & G. Nicolson proposed
that membrane proteins are inserted into the
phospholipids bilayer
It’s like a fluid…
It’s like a mosaic…
It’s the
Fluid Mosaic Model!

8. Phospholipids
Fatty acid
Phosphate
• Fatty acid tails
– hydrophobic
• Phosphate group head
– hydrophilic
• Arranged as a bilayer
Aaaah,
one of those
structure–function
examples

9. 1. Extrinsic membrane proteins are loosely held
to the surface of the membrane and they can be
easily separated e.g. cytochrome c of
mitochondria.
2. Intrinsic membrane proteins are tightly
bound to the lipid bilayer and they can be
separated only by the use of detergent or
organic solvents e.g. hormone receptors.

10. Membrane is a collage of proteins & other molecules
embedded in the fluid matrix of the lipid bilayer
Extracellular fluid
Cholesterol
Cytoplasm
Glycolipid
Transmembrane
proteins
Filaments of
cytoskeleton
Peripheral
protein
Glycoprotein
Phospholipids

11. • Transport across the membranes
• The biological membrane are relatively
impermeable.
• The membrane, therefore forms a barrier for the
free passage of compounds across it.
1. Passive diffusion
2. Facilitated diffusion
3. Active transport

12. Passive transport
• Passive transport is the diffusion of substances
across a biological membrane.
• This occurs without the use of cellular energy.

13. 2.Facilitated diffusion: This is somewhat
comparable with diffusion solute moves along
the concentration gradient (from higher to lower
concentration) and no energy is required.
• But the most important distinguishing feature is
that facilitated diffusion occurs through the
mediation of carrier or transport protein.
• Specific carrier protein for the transport of
glucose, galactose, leucine, phenylalanine etc.
have been isolated and characterized.

14. • Mechanism of facilitated diffusion: A ping pong
model is put forth to explain the occurrence of
facilitated diffusion.
• According to this mechanism, a transport protein
exists in two conformation, in the pong
conformation it is exposed to the side with high
solute concentration.
• This allow the binding of solute to specific sites on
the carrier protein.
• The protein then undergoes a conformational
change(ping state) to expose to the side with low
solute concentration where the solute molecule is
released.
• Insulin increases glucose transport in muscle and
adipose tissue.

16. 3.Active transport: Active transport occurs
against a concentration gradient and this depend
upon the supply of metabolic energy (ATP).
• Active transport is also carrier mediated process
like facilitated diffusion.
• The most important primary Active transport
systems are ion pumps.

17.  Na+- K+ pump
 The cells have high intracellular K+
Concentration and low Na+ concentration.
 This is essentially needed for survival of cell.
 High cellular K+ is required for the optimal
glycolysis (pyruvate kinase is depend upon K+)
and for protein biosynthesis.
 Further Na+ and K+ gradients across plasma
membrane are needed for the transmission of
nerve impulses.

18. • Na+-K+ pump is responsible for the maintenance
of high k+ and low Na+ concentration in the cells.
• This is brought about by an integral plasma
membrane protein, namely the enzyme Na+-K+
ATPase.
• It consist of two α and two β subunits which may
be represented as [αβ]2 .
• Na+-K+ ATPase pump 3Na+ ions from inside the
cell to outside and bring 2k+ ions from outside to
inside with a concomitant hydrolysis of
intracellular ATP.
3Na+ (in)+ 2K+ ( out) +ATP 3Na+ (out)+ 2K+ (in)+ ADP+Pi

20. • Ouabain inhibit Na+-K+ ATPase pump.,
• Ouabain is a steroid derivative extracted from
the seed of an African Shrub.
• It is a poison used to tip the hunting arrows by
the tribal in Africa.

21. Transport summary
simple
diffusion
facilitated
diffusion
active
transport
ATP

22. Transport system
1. Uniport system: This involves the movement of
a single molecule through the membrane. E.g.
transport of glucose to the erythrocytes.
2. Symport system: the simultaneous transport of
two different molecules in the same direction.
E.g. transport of Na+ and glucose to the
intestinal mucosal cells from the gut.
3. Antiport system: The simultaneous transport of
two different molecules in opposite direction e.g.
exchange of Cl- and HCO-3 in the erythrocytes.

23. • Proton pump in stomach
• This is an antiport transport system of gastric
parietal cells.
• It is brought out by the enzyme H+ - K+ ATPase
to maintain highly acidic condition in the lumen
of stomach.
• Proton pump antiport two cytoplasmic proton
(2H+) and two extracellular potassium (2K+)
ions for a molecule of ATP hydrolyzed.
• The chloride ions secreted by Cl- channel
combine with proton to form gastric HCl.

24. • Passive transport of water-osmosis.
• Osmosis is phenomenon of movement of water
from low osmotic pressure (dilute solution) to
high osmotic pressure (concentrated solution)
across biological membrane.
• The movement of water in body occurs through
osmosis, and this process does not require
energy.
• Certain medical and health complication are due
to disturbance in osmosis e.g. edema, cholera,
diarrhea, inflammation of tissue.

25. OSMOSIS

26. • Transport of macromolecules
• The transport of macromolecule such as protein,
polysaccharides and polynucleotide across the
membrane is equally important.
1. Endocytosis : Intake of macromolecules by the
cells.
• It is estimated that approximately 2% of the
exterior surface of plasma membrane possesses
characteristic Coated-pits.
• The pits can be internalized to form coated
vesicles which contain an unusual protein called
Clathrin.
• The uptake of LDL molecules by the cells is a
good example of endocytosis.

27. • Endocytosis occurs when
the plasma membrane is
pulled inwards and will
form a “pocket” around a
particular substance.
• The substance will become
enclosed in the vesicle
which is then pinched off
and begins moving through
the cytoplasm.
• Cells can bring in solids and
liquids using this process.

28. 2.Exocytosis: Release of macromolecules from
the cells to outside.
• The release of macromolecules to the outside of
the cells mostly occurs via the participation of
Golgi apparatus.
• The macromolecules are transported to the
plasma membrane in a vesicles and let out.
• The secretion of hormone e.g. Insulin usually
occur by Exocytosis.

29. • Exocytosis is internal
vesicles will fuse with
the plasma membrane
and the contents of the
vesicle are released into
the external
environment of the cell.
• The cell can secrete
substances they
produced this way or
excrete waste products.

30. Diffusion

31. Active transport
• The movement of a substance across a
biological membrane against its concentration
or electrochemical gradient with the help of
energy input and specific transport proteins.
• This movement of particles occurs against the
concentration gradient or from an area of low
concentration to an area of high concentration
with the use of ATP.

32. Active Transport

33. Pinocytosis
• A type of endocytosis in
which the cell ingests
extracellular fluid and
its dissolved substances.

34. 10. Use the sodium-potassium pump to explain how active transport
can be used to move particles against a concentration gradient.
• The cell can hydrolyze ATP and use the energy
released to move substances across the plasma
membrane and against the concentration gradient.
The energy is used to change the shape of membrane
protein “pumps”.
• Each pump only transports particular substances.

35. 10. Use the sodium-potassium pump to explain how active transport can be
used to move particles against a concentration gradient.
• The particle will enter the pump on the side with a
lower concentration and bind to a specific site for that
type of particle.
• Energy from ATP is used to change the shape of the
pump, the particle is released on the side of higher
concentration, and the pump returns to its original
shape.

36. 9. Compare active and passive transport.
• Passive transport is the diffusion of particles
across a biological membrane. This occurs
without the use of cellular energy.

37. 9. Compare active and passive transport.
• Active Transport is the movement of particles
across biological membranes using energy
from ATP. This movement of particles occurs
against the concentration gradient or from an
area of low concentration to an area of high
concentration.

38. How about large molecules?
• Moving large molecules into & out of cell
– through vesicles & vacuoles
– endocytosis
• phagocytosis = “cellular eating”
• pinocytosis = “cellular drinking”
– exocytosis
exocytosis

39. Transport summary
simple
diffusion
facilitated
diffusion
active
transport
ATP

40. Membrane Proteins
• Proteins determine membrane’s specific functions
– cell membrane & organelle membranes each have unique
collections of proteins
• Membrane proteins:
– peripheral proteins
• loosely bound to surface of membrane
• cell surface identity marker (antigens)
– integral proteins
• penetrate lipid bilayer, usually across whole membrane
• transmembrane protein
• transport proteins
– channels, permeases (pumps)