Viruses

Er. Mohit Rawat B.Tech ,MBA,M.Tech

Assistant ProfessorDepartment 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…

T4 BacteriophageTobacco Mosaic

Virus Influenza Virus

Head

Tail sheath

DNA

Tail fiber

RNACapsid

Surfaceproteins Membrane

envelope

RNA

Capsidproteins

• 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

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!

virusInjecting DNA

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

Rabies: only nervous system cells of mammals

Common cold: infects cells on airway passage to lungs

Tobacco mosaic virus: only tobacco plants…not wheat or corn

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?

Bacteriophage enzyme lyses thebacterium’s cell wall, releasingnew bacteriophage particles thatcan attack other cells.

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 injects DNA into bacterium

Bacteriophage attaches to bacterium’s cell wall

Bacteriophage

Bacteriophage DNA

Bacteriophage protein

Bacteriophage protein coat

Bacteriophage DNA

Bacterialchromosome

Lytic Cycle

Section 19-3

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 tissue-regenerating 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, three-dimensional 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 self-assembly 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 voltage-controlled 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 site-directed 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