1. Presented by : Saurabh Pandey
PALB-3252
Jr.M.Sc. (Agri) Plant Biotechnology
Submitted to: Dr. Dayal Doss
Professor
Dept. of Plant Biotechnology
27/11/13 1
4. INTRODUCTION
Biological membranes are thin, flexible surfaces separating cells and cell
compartments from their environments.
Different membranes have different properties, but all share a common architecture.
Membranes are rich in phospholipids, which spontaneously form bilayer structures in
water.
Membrane proteins and lipids can diffuse laterally within the membrane, giving it the
properties of a fluid mosaic.
Membranes are asymmetric; interior and exterior faces carry different proteins and
have different properties.
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5. HISTORY
1895-Charles Ernest Overton in his book on anesthesia called layers
surrounding cells as ”lipoids” made of lipids and cholesterol.
1925-Gorter and Grendel proposed lipid bilayer model of cell membrane
based on their experiment on RBCs extract of different animals.
1935-Danielli and Davson earliest molecular model of biomembranes
including proteins with lipids.
1958-Robertsons says two protein layers are adsorbed to lipid bilayer. All
membrane have same composition.
1972- The Fluid Mosaic Model of Singer and Nicolson.
1984-The Mattress Model by Mouritsen and Bloom.
In 1984, Mouritsen and Bloom (1984) proposed the mattress model that
suggests that proteins and lipids display interactions with a positive free
energy content due to variations in the hydrophobic length of the molecules
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6. The typical thickness of a lipid bilayer is about 5 nm.
If the hydrophobic core of a membrane protein is longer or shorter than this length, either some
hydrophobic protein or lipid segments are exposed to water, or the lipid membrane has to be deformed
to compensate for unfavorable hydrophobic interactions.
This effect is called as ‘hydrophobic matching’.
The hydrophobic matching give rise to interfacial tensions between lipids and proteins. These tensions
may result in accumulation of certain lipids around the proteins. And in the mutual attraction of proteins
due to capillary forces, leading to aggregation and clustering of proteins.
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8. S.J.SINGER AND G. NICHOLSON FLUID MOSAIC MODEL(1972)
Universally accepted model for all kinds of biological
membranes.
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9. Assembly of Phospholipid bilayer and Protein embedded in it
The relative amounts of protein and lipid vary significantly , ranging from
about 20%(dry wt.) protein(in myelin) to 80% protein(in mitochondria)
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14. 14
ALCOHOLS IN BIOLOGICAL MEMBRANES
Decide about the properties of the phospholipid
When cleaved become important signaling molecules
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15. 15
• Fatty acid end of a phospholipid
molecule is strongly nonpolar
(hydrophobic)
• Forms internal tails in the membrane
• Usually even number of carbons
• Myristate : 14
• Palmitate: 16
• Arachidonate: 20
• Double bonds in unsaturated fatty
acid create a bend and “loosen up”
membrane packing
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FATTY ACIDS
18. 18
Another class of
membrane lipids
All have four hydrocarbon
rings
Cholesterol has a hydroxyl
substituent on one ring
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Sterols
19. Fig: Cholesterol
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• Hydroxyl group can
interact with water what
makes the molecule
amphipathic.
• Cholesterol is very
abundant an necessary in
of eukaryotic cells
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Cholesterols
20. Fig: Phospholipid bilayer
20
In a bilayer Fatty acid tails
point inward
Alcohol heads point outward
Each phospholipid layer is
called a leaflet
Leaflets are different in
composition
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Phospholipid bilayer
21. How Do The Phospholipid Bilayers Form?
Driving force are hydrophobic interactions
between the fatty acid chains of phospholipids
and glycolipids molecules.
Hydrogen bonds between polar groups stabilize
the bilayer.
Phospholipids in biological membranes are
synthesized in 2-step enzymatic reaction.
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22. Synthesis Of Membrane Lipids
(A). Two fatty acids are added
to glycerol 3- phosphate to
produce phosphatidic acid
(acyl transferases)
• This steps enlarges lipid
bilayer.
(B). Phosphatase and
phosphotransferase attach
head groups
• This steps determines the
chemical nature of lipid
bilayer
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23. 23
Physical properties of the phospholipid bilayer
• Highly dynamic.
• Lateral mobility.
• Flipping between
leaflets.
• Imperfectly packed fatty
acid chains (double
bonds in fatty acid
chains) are responsible
for membrane
permeability.
• High electrical resistance
• Impermeable to ions
• Permeable to gases and small
lipid soluble
molecules
• Slightly permeable to water
• Ability to self seal (always form
closed
compartments)
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24. MEMBRANE PROTEINS
• Each cell membrane has a
set of specific membrane
protein .
• Membrane proteins allow
the membrane to carry out
its distinctive functions
• Membrane proteins are
either integral (intrinsic) or
peripheral
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25. 25
Integral (intrinsic) membrane Proteins
• Cross the bilayer
(transmembrane)
• Transmembrane segment is
usually α helix
• A segment of 25 hydrophobic
residues
• Examples: G protein coupled
receptors, ion
channels, pumps,
transporters
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26. 26
Examples of intrinsic membrane proteins
(A) Glycophorin
• Single transmembrane
domain protein
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(B) Bacteriorhodopsin
• Multiple transmembrane
domains protein
27. 27
• Do not interact with
hydrophobic core of
the bilayer
• Are associated with
membrane through
lipid anchors
• Interactions with
bilayer (but not
complete crossing) or
contact with integral
membrane proteins
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Peripheral membrane proteins
28. Functions of membrane proteins
• Transport of nutrients
• Passage of water
• Selective transport of molecules
(keep the unwanted molecules out,
secrete metabolic by products)
• Maintenance of proper ionic
composition inside the cell
• Reception of signals from the
extracellular environment
• Expression of cell identity
• Physical and functional
connection with other cells or
the extracellular matrix (in
multicellular organisms)
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29. Asymmetry Of The Membrane
The two faces of a membrane are asymmetrical in lipid and
protein composition
All integral and membrane bound proteins are distributed
asymmetrically
Each protein has a single, specific orientation with respect
to cytosolic and exoplasmic faces of the membrane
Glycolipids are located exclusively on the exoplasmic leaflet
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31. 31
Plasma membranes have different protein:lipid ratio
Protein: lipid ratio in the membrane
depends on the function
Mitochondrial membrane is 76% protein
(has many transporters and enzymes).
Also in purple membrane of halobacteria
Myelin (Schwann cell) membrane has
18% protein (phospholipids are great
insulators)
Fig: Light harvesting complex of purple bacteria
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32. FUNCTIONS
SELECTIVE PERMEABILITY
PINOCYTOSIS
CELL RECOGNITION
BIOGENESIS OF CELL ORGANELLES
OXIDATIVE PHOSPHORYLATION IN MITOCHONDRIA MEMRANE
ABSORPTION AND SECRETION IN INTESTINAL CELLS
AS A HORMONE RECEPTOR SITES
CELL ADHESION
TRANSMISSION OF NERVE IMPULSE
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40. WHAT ARE BIOFILMS
• Biofilms are colonies of
living micro-organisms (e.g.,
bacteria, fungi, algae, and/or
protozoa) growing on any
surface (e.g. metals, plastics,
tissue, soil particles, teeth, and
so forth)
• Biofilms are surface-attached
communities of bacteria,
encased in an extracellular
matrix of secreted proteins,
carbohydrates, and/or DNA,
that assume phenotypes
distinct from those of planktonic
cells
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41. HISTORY
In 1684 Anthony van Leeuwenhoek remarked on the vast
accumulation of microorganisms in dental plaque in a report to the
Royal Society of London: "The number of these animicules in the scurf
of a man's teeth are so many that I believe they exceed the number of
men in a kingdom
In a 1940 issue of the Journal of Bacteriology, authors H. Heukelekian
and A. Heller wrote, "Surfaces enable bacteria to develop in
substrates otherwise too dilute for growth. Development takes place
either as bacterial slime or colonial growth attached to surfaces."
Claude ZoBell described many of the fundamental characteristics of
attached microbial communities in the 1940s
The earliest use of “biofilm” in publication is in the Swedish
journal Vatten: Harremoës, P. 1977. “Half-order reactions in biofilm
and filter kinetics,” Vatten, 33 122-143
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42. CONTINUED...
The earliest use of “biofilm” in publication is in the Swedish
journal Vatten: Harremoës, P. 1977. “Half-order reactions in
biofilm and filter kinetics,” Vatten, 33 122-143
In 1990, recognizing the significance of microbial activity, as well
as the tremendous economic costs associated with microbial
communities on surfaces, the US National Science Foundation
founded the Center for Biofilm Engineering at Montana State
University in Bozeman (though, interestingly, NSF would not
initially accept the word “biofilm” in the Center’s name; instead
the award funded the “Center for Interfacial Microbial Process
Engineering”)
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43. FORMATION OF BIOFILMS
Form in places with
access to water
Attach to a solid
surface using several
means of Flagella,
Hydrophobic Cell Walls
& Sticky Polymers
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44. STEPS IN BIOFILM FORMATION
Interaction of cells with a surface or
with each other
(A)
• Initiation of biofilm
formation
(B)
• Films aggregate
(C)
• Cells form an
extracellular matrix
• Structure of biofilms are dramatically different due to the
specific organisms in the film and environmental conditions
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46. STRUCTURE OF BIOFILMS
Key components of the Biofilm
matrix are extracellular
polysaccharides and proteins
Dead cells have also been
identified in biofilms
Extracellular DNA is also
important
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47. Polysaccharides in Biofilms
Carbohydrates significantly impact bacterial
virulence
Bacteria have capsular polysaccharides and
exopolysaccharides
The polysaccharides are not soluble and do
not disassociate with the bacterial cells
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48. The biofilm associated protein (BAP)
Structurally similiar to the surface proteins
Esp of Enterococcus faecalis
mus20 of Pseudomonas aeruginosa
sty2875 of Salmonella typhi
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49. PATHOGENS THAT HAVE BEEN STUDIED FOR THE
FORMATION OF BIOFILMS
Staphylococcus aureus- for urinary catheters in medical industry
Staphylococcus mutans-In human dental caries
Salmonella typhi-For microbial cantamination of food in food industry
Enterococcus faecalis-Endocarditis and biofilm associated pili
Pseudomonas aeruginosa- tobramycin resistance and growing on urinary
catheters
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50. GENES AND BIOFILMS
In November 2005,Biologist Alejandro Toledo
Arana has identified two genes(arlRS,sarA)
that regulate the formation of biofilms in
Staphylococcus aureus
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51. Submerged biofilms seems to form columns and
mushroom like projections that are separated by water-filled
channels
Floating biofilms form a skin or pellicle at the air- liquid
interface – shows organization of cells with the matrix at
the outside
Films that form on the surface of solid media such as agar
or other surfaces
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52. CONTINUED……
Top to bottom gradient of decreasing antibiotic susceptibility
The gradient originates in the surface layers of the biofilms
where there is complete consumption of oxygen and glucose
There are patches of antibiotic resistance at the surface
Proximity of cells lead to horizontal transfer of genes for
resistance
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53. BIOFILMS –QUORUM SENSING
Certain species of bacteria
communicate with each other
within the biofilm. As their
density increases, the
organisms secrete low
molecular weight molecules
that signal when the population
has reached a critical threshold.
This process, called quorum
sensing, is responsible for the
expression of virulence factors.
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54. USES OF BIOFILMS
Often used to purify water in water treatment
plants
Used to break down toxic chemicals
Used to produce useful biological compounds,
including medicines
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56. Tend to clog pipes and
water filters
Can cause numerous diseases,
including many diseases
prevalent in hospitals
Extra-resistant to antibiotics
Can form almost anywhere that water is present, including
catheters, kitchen counters, etc.
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57. AGENTS FOR DESTRUCTION OF BIOFILMS (INDUSTRIAL BIOCIDES)
(Alexidine, Chlorhexidine, Polyhexamethylene
biguanides), monophenylethers
(Phenoxyethanol) and quaternary amonium
compounds (Cetrimide, Benzalkoniums) and
have demonstrated biochemical bases for the
activities and associated mammalian cell
toxicities of thiol interactive agents (bronopol,
isothiazolones).
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58. INDUSTRIAL APPLICATIONS
Bioremedation-Bacterial
degradation of polluting
environments.(Pseudomonas
aeruginosa)
Biofilteration-Selective removal
of chemicals in solution. Use of
Moving Bed Biofilm Reactor
Technology.
Biobarriers-Protection of objects
using extremely rugged
glycocalyx produced by
biofilms.(Grodonia
polyisoprenivorens)
Bioreactors-Production of
compounds using engineered
biofilms.
BIOFILMS IN MEDICAL DEVICES-
•Contact lenses
•Central venous catheters
•Endotracheal tubes
•Intrauterine devices
•Mechanical heart valves
•Pacemakers
•Dialysis catheters
•Urinary catheters
•Voice prostheses
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