Viruses are obligate intracellular agents that contain nucleic acids and have a protein capsid. They lack cell structures like cell walls and ribosomes. Viruses vary greatly in size and shape. The virus structure consists of the genome, capsid, and some have an envelope. The genome can be DNA or RNA. Capsids are protein shells that protect the genome and come in different symmetries like icosahedral or helical. Some viruses have an outer envelope of lipids and glycoproteins. Modern microbiology applies microbes to fields like medicine, biotechnology, food production, and more.

1. Microbiology seminar
Submitted by
MAYA.P.R

2. GENERAL STRUCTURAL
PROPERTIES OF VIRUS
&
MODERN AGE OF MICROBIOLOGY

3.  Virus is the obligate intracellular agents
contain one type of nucleic acid(DNA/RNA)
 Genome enlosed within capsid and it
surrounded by lipid containig membrane
called envelop
 The entire virus: nucleic acid capsid envelop
and glycoprotein spikes altogether call virion
 Virus donot have cellwall, ribosoms,cellular
enzymes, no sensitivity to antibacterial
angents
 It occupies in between living and non living
organisms

4.  Origin of virus is not known
 2 hypothesis on viral origin
 First hypothesis states that the virus derived
from the host cell that replicate
autonomously and it evolve independently
 Second hypothesis states virus derived from
intracellular parasites like bacteria
 On the basis of host specificity virus grouped
into 4:animal virus, plant virus,insect virus
and bacterial virus(bacteriophage)

5.  Viral size ranges from 20-400nm
 Largest virus-small pox virus -400nm
 Smallest virus –parvovirus -20nm
 Parvovirus smallest than bacteria it is
filterable and cannot observe under light
microscope only in ultra microscope
Parvo virus
Smallpox virus

6. Techniques used to identify size of virus
 Passing them in colloidal membrane filters of
different pore size
 Measured by centrifuge
 More accurate method is electron microscopy
 Shape of virus varies in different groups
 Most animal virus are sperical, but pox virus
is rectangular, rabies virus is bullet shaped
tobacco virus is rod shaped and some are
irregular also

7. Filament-shape Brick-shape Tadpole-shape
O
Spherical-shape Rod-shape Bullet-shape

8.  A simple virus consist of DNA/RNA packaged into
capsid called nucleocapsid
 Some virus have additional protective layer
called envelop
 Virus without envelop called naked
 genome
 either dna/rna as nucleic acid
 RNA virus single stranded and DNA virus double
stranded
 Genome can be linear or circular
 Most have linear genome except papova virus it
have supercoiled circular DNA

9. Capsid
it is protein shell that encloses
nucleic acid
It composed of protein subunit
capsomeres and capsomeres made
up of polypeptides called protomers
Function of capsid
Protect nucleic acid from nucleases
Helps in adsorbance and penetration

10. Symmetry of capsid
Capsid arrage symmetrically along
nucleic acid
Virus grouped based on capsid
symetry into 3
 icosahedral,helical,complex
 Icosahedral capsid
• It is a polygon with 12 corners and
20 faces
• Each face is a equilateral triangle
• Pentagonal capsomers and
hexagonal capsomeres found

11.  Pentagons touch 5nighbours and hexagonal touch
6 neighbours
 Always have 12 pentagons but hexagons may
vary
 Most icosahedral virus was naked
 It is most stable
 They have viral attachment proteins(vap’s)on the
surface binds to target cells
 Example;herpes,retro,adeno,flavi viruses

12. Helical capsid
Multiple copies of polypeptide
capsomers with nucleic acid together
form helical or spiral tube shape
 it is rod shaped
 nucleiocapsid coiled around envelop
All are rna virus and enveloped
example:rhabdovirus

13. Complex capsid
 Donot have icosahedral or helical structure
becz of its complexicity
 Example; pox virus,bacteriophage

14.  It is a lipid bilayer
 It have always virus encoding glycoproteins
protruding from envelop and exposed on the
external surface of virion
 These glycoprotein projection is called
peplomeres
 For many virus it seems like spikes
 A virus contain more than one type of
peplomer eg;influenza virus

15.  2 peplomeres of influenza virus is haemagglutin and
nueraminidase
 haemagglutin is triangular shaped and
nueraminmidase is mashrroom shaped
 Peplomeres have 2 function
 Promote interraction with nucleocapsid
 Act as VAP ,vap bind with erythrocytes called
haemagglutin

17.  Microbiology has long rich history
 It initially centered on causes of infectious
diseases but now it includes practical applications
of science
 Many individuals gave significant contributions
 Golden age of microbiology: at the first dacade of
1900s many agents of infectious diseases were
identified
 It leading to reduce the spreading of micro
organisms
 After world war II antibiotics is introduced to
medicine,it reduces the incidence of pneumonia ,
tuberculosis, meningitis, syphilis

18.  In 1940s electron microscope invented in that
decade cultivation of viruses are introduced and
knowledge of virus is developed
 Development of vaccines in 1950s were reduce
the incidence if viral diseases like polio ,
Measeles, mumps and rubella
 modern age of microbiology reaches into many
fields:-
 development of pharmaceutical
 quality control products in dairy and food
production
 Control of infectious micro organisms in
consumable water

19.  Industrial application of micro organisms
 To produce vitamines,amino acids,enzymes,
growth suppliments
 Manufacture foods like fermented dairy
products –sour cream, buttermilk,yogurt
 Fermented foods are pickles , bread , alcahol
 Major area of applied microbiology is
biotechnology
 In biotechnology micro organisms used as living
factories to produce pharmaceuticals include
insulin,interferons,blood clotting factors,clott
dissolving factors enzymes and vaccines.