The plasma membrane, also called the cell membrane, is the membrane found in all cells that separates the interior of the cell from the outside environment. . The plasma membrane consists of a lipid bilayer that is semipermeable. The plasma membrane regulates the transport of materials entering and exiting the cell.

1. Plasma Membrane
&
Transport System
By
Dr. Rachana Choudhary
Asstt. Prof. Microbiology
Shri Shankaracharya Mahavidyalaya
Junwani Bhilai

2. Introduction
 The plasma membrane is an envelop
surrounding the cell, also known as a boundary
for the Cytoplasm.
 It separates and protect the cell from the
external environment.
 Plasma membrane also provide a connecting
system between the cell and its environment
 Term Plasma Membrane was introduced by nageli
in 1855.
 Occurrence
 Thickness -75 A0

3. • Chemical composition
• The membranes are composed of
• Lipids
• Protein
• Carbohydrates
• Salt
• Water

4. Ultrastructure
 Bimolecular Leaflet Model (Danielli &
Davson 1935)
 Lattice Model(Wolpers 1941)
 Micellar Model(Hilleir & Hofmann 1953)
 Trilaminar Model(Robertson 1960)
 Fluid Mosaic Model (Singer & Nicolson
1972)

5. • 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.

6. 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!

7. Phospholipids
Fatty acid
Phosphate
• Fatty acid tails
– hydrophobic
• Phosphate group head
– hydrophilic
• Arranged as a bilayer

8. 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.

9. 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

10. Function of Plasma Membrane
 Mechanical Support
 Biogenesis of Cell Organelles
 Cell Recognition
 Antigenic Specificity
 Transmission of Nerve Impulses
 Exchange of material or Cell Permeability

11. Transport across the membranes
there are two main types of cellular transport
distinguished by palade (1966)
PERMEATION
BULK Transport
1. Simple or 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.

15. 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.

16. 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.

17. • Na+-K+ pump is responsible for the maintenance
of high k+ and low Na+ concentration in thecells.
• This is brought about by an integral plasma
membrane protein, namely the enzyme Na+-K+
ATPase.
• 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

18. Neutral Na+-K+ Pump

19. Electrogenic Na+-K+ Pump

20. Transport summary
simple
diffusion
facilitated
diffusion
active
transport
ATP

21. 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.

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

23. • Transport of macromolecules(Bulk Transport)
• 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.

24. Phagocytosis
Phagocytosis Cell eating is
the process by which a cell
uses its plasma membrane to
engulf a large particle (≥ 0.5
μm), giving rise to an internal
compartment called the
phagosome. It is one type of
endocytosis.

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

26. 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.

27. • 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.
substances
• The cell can secrete
they
produced this way or
excrete waste products.

28. Reference
 Text book of microbiology –R.P.Singh
 General Microbiology –Pawar & Doginawala Vol -1
 Botany – Y.D. Tyagi
 Text book of microbiology –Dubey and Maheshwari
 Google search

29. THANK YOU