Download Bacteria and Viruses

Viruses
Er. Mohit Rawat
B.Tech ,MBA,M.Tech
Assistant Professor
Department of Nanotechnology
What is a Virus?
• A virus is a noncellular particle made up
of genetic material and protein that can
invade living cells
• Structure
– Core of nucleic acid surrounded by a protein
coat called a capsid
– Capsid can be DNA or RNA, but not both
– Core can be several to several hundred
genes
SO HOW BIG ARE
VIRUSES???
• Viruses are REALLY
small.
• They are much smaller
than bacteria.
• They can only be seen
with an electron
microscope.
Bacteriophage
• Bacteriophages are viruses that infect
bacteria
• Bacteriophage
– Head – capsid and DNA
– Tail – with fibers to attach to bacteria
T group
• Most commonly studied are T group – T1,
T2, T3, T4 etc...
• T4 has a DNA core within a protein coat,
and tail with tail fibers to attach to bacteria.
Viral shapes
• Variety of shapes
– Rod
– Tadpole
– Many sided, helical or cubelike
VIRUS SHAPES
• Round
• Rod-shaped
• Many sided
(icosohedral)
SHAPES MAY DIFFER BUT…
• All viruses have
• 1. Chromosome-like part that carries hereditary information – The Core
• 2. Protein coat: Protects hereditary information and provides the shape! The
Capsid
Tobacco Mosaic
Virus
T4 Bacteriophage
Head
DNA
Influenza
Virus
RNA
Capsid
proteins
Capsid
RNA
Tail
sheath
Tail
fiber
Surface
proteins
Membrane
envelope
ROUND VIRUSES
• Herpes virus
–There are
two types:
• Genital
• oral
ROD-SHAPED
• Tobacco
mosaic
virus
MANY SIDED
• bacteriophage
E coli bacteria
Is this why viruses infect us?
• YES!
• Viruses need
living
organisms in
order to
reproduce and
form more
viruses!
Injecting DNA virus
Virus Size
• Size – 20 to 400 nanometers (one
nanometer is one billionth of a meter)
• Specificity – usually infect specific
organisms
– Cannot infect animals if it infects plants
– Some can infect wider variety
– Rabies – all mammals, some birds
VIRUSES ARE SPECIFIC IN
THE CELLS THEY INFECT
Tobacco mosaic virus: only tobacco
plants…not wheat or corn
Rabies: only nervous system cells of mammals
Common cold: infects cells on airway passage to
lungs
Lytic Infection
•
Cause cells to lyse or burst
1. Infection – chance contact virus with right kind of bacterium. Virus
attaches to bacterium and injects its DNA. Most times, complete
virus particle does not enter.
2. Growth – Bacterium can’t tell difference between bacterial and viral
DNA. RNA polymerase causes mRNA to be made from cell for
virus. Viral DNA takes over and produces more DNA and viral
proteins.
3. Replication – Virus uses bacterial material to make thousands of
copies of the protein coat and DNA. Cell becomes filled with virus
particles. (All three stages can happen with E. coli within 25
minutes!)
4. DNA serves as central point for virus particles to be assembled.
Cells fill with virus and lyse (burst). New viruses can now infect new
cells.
SO HOW DO VIRUSES CAUSE
DISEASE?
Section 19-3
Bacteriophage
protein coat
Bacteriophage DNA
Bacterial
chromosome
Bacteriophage attaches to
bacterium’s cell wall
Bacteriophage enzyme lyses the
bacterium’s cell wall, releasing
new bacteriophage particles that
can attack other cells.
Lytic Cycle
Bacteriophage injects DNA
into bacterium
Bacteriophage proteins and
nucleic acids assemble into
complete bacteriophage
particles
Bacteriophage takes over
bacterium’s metabolism, causing
synthesis of new bacteriophage
proteins and nucleic acids
Bacteriophage
Bacteriophage DNA
Bacteriophage protein
Retroviruses
• RNA viruses
• When they infect a cell, they produce DNA
copies of their RNA genes.
• Retroviruses have their genetic information
copied backwards. RNA  DNA
• One retrovirus is HIV. Others cause cancer in
animals and humans.
• The theory is that viruses were not the first living
things. They are dependent on living things to
survive.
Viruses and Disease
• Examples are:
–
–
–
–
–
–
–
–
–
–
Small Pox
Polio
Measles
AIDS
Mumps
Influenza
Yellow Fever
Rabies
Common Cold
Ebola etc…
Vaccine
• The body’s own defenses must be used
• Vaccine – dead or weakened viruses that
stimulate the bodies defense system
• Symptoms can be treated sometimes, but
once someone is infected by a virus, there
is not much science can do
Engineering virus particles for new
technological materials
and nanostructures
• There is already a plethora of novel
nanomaterials and nanostructures that are
being developed for multiple biomedical,
mechanical, electrical, electronic, optical
or other nanotechnological applications.
Some novel hybrid nanostructures
include engineered viral particles
• One important goal in materials science is
the development of methods for the
spatially constrained formation of inorganic
nanoparticles or organic polymers.
• Engineered virus particles are being used
also as nanometric-sized building blocks
for the hierarchical assembly of hybrid
materials with distinct one-, two- or three
dimensional structures
• Amino acid residues on the viral particle surface, either
naturally occurring or introduced by protein engineering,
were functionalized with an appropriate chemical
group.The viral particle was engineered to display a
peptide able to bind a non-biologic ligand, including
inorganic materials. The peptides were chosen because
of their binding specificity (e.g. for a metal), or selected
by molecular display. These modifications are intended
to nucleate and control the organization and growth of
the structure. The nanostructured materials thus formed
may be further functionalized and or the eventual
construction of nanodevices
• A medically important application of the strategy
just outlined is the development of tissueregenerating materials. In one example, the long
rod-shaped phage M13 was engineered to
display cell signaling peptides, which allowed
their self-assembly in an organized, threedimensional array of viral nanofibers; these
scaffolds were able to support cell proliferation
and differentiation, as well as oriented cell
growth in three dimensions
• Another promising application is the development of
nanostructures that could be used as components of
future electronic devices For example, M13 phages were
engineered to display gold binding motifs on the capsid
and streptavidin-binding moieties at one end, and used
to assemble Au and CdSe nanocrystals into ordered
monodimensional
arrays
and
more
complex
nanoarchitectures .Such monodimensional arrays could
be used to nucleate electrically conductive nanowires.
Engineered M13 phages were also used for the selfassembly of gold-cobalt oxide nanowires
• that could be used as electrodes to fabricate thin, flexible
Li-ion batteries .
• M13 phages engineered to have specific, peptide based
recognition sites for ZnS, CdS, CoPt or FePt were used
as templates for ordering quantum dots nanometricsized
semiconductor crystals that can act as inorganic
fluorophores) in self-assembled, semi-conducting or
magnetic nanowires (
• Engineered cowpea mosaic virus (CPMV) has been also
used as a scaffold to build electrically conductive
molecular networks. Cysteine residues were introduced
by protein engineering at defined positions of the capsid
surface, which allowed the anchoring of gold particles
that were subsequently interconnected by molecular
wires, to create a three-dimensional conducting network
on each viral particle. The nanoparticles were then
interconnected using thiol terminated organic molecules.
Different structures were constructed, including voltagecontrolled switchable networks that could be used in
memory nanocircuits
• Tobacco mosaic viruses (TMV) with
platinum nanoparticles attached behaved
as memory elements that could be also
switched on and off electronically
• Materials-related application of engineered viral particles is the
development of nanobio sensors.
• Nanobiosensors are nanometric-sized sensors based on
immobilized biomolecules that specifically bind a target ligand
(analyte). As one example, virus particles were engineered by sitedirected mutagenesis to bind both nickel nanohairs and antibodies
against troponin I, a protein marker found in patients with a higher
risk of heart attacks. In this way, a regular threedimensional
array with a very high density of anti-troponin I antibodies could be
formed, and was used as an ultrasensitive biosensor to detect
extremely low levels of troponin I
M13 virus li Ion battery