Viruses are obligate intracellular parasites that are much smaller than bacteria, ranging from 20-300nm in size. They do not have cells and are composed only of nucleic acids surrounded by a protein capsid. Viruses can have either DNA or RNA, which may be single or double stranded. Viruses replicate only inside living host cells by using the host's cellular machinery. Viruses have different symmetries depending on their shape, including icosahedral, helical, and complex. Bacteriophages are viruses that infect bacteria and have a distinctive binal symmetry with an icosahedral head and helical tail. Viruses are inactivated by heat, chemicals, and lipid solvents depending on whether they have an

1. Structure of Viruses
Pharmaceutical Microbiology
and Immunology
S.Y. B.Pharm.
Mrs. V. A. Warad

2. Objectives
• Explain concept of viruses, in relation to other microorganisms
• Describe important morphological and chemical features of viruses
• Understand the salient features of viral replication cycle
• Understand methods of virus cultivation
• Describe role of viruses in cancer

3. Virus introduction – general
characters
Lecture I

4. Introduction
• Viruses are obligate intracellular parasites of human,
animals, plants, bacteria.
• They are 20-300 nm in size.
• Ultramicroscopic (seen only under electron
microscope)

6. Introduction
• Filterable (Pass through bacteria proof filter)
• They do not have their own metabolic machinery.
• They can not be cultivated in nutrient media.
• They reproduce only in living cells

7. Structure of virus
• They do not have cellular structure. - acellular
• They are nucleocapsids / nucleoproteins.
• They have only one type of nucleic acid, either DNA or RNA.

8. Structure of virus
• Nucleic acid is enclosed in capsid.
• Function of capsid:
• Protection to NA
• Attachment to host cell surface
• Capsid is made up of protein.
• Capsid is made up of morphological subunits called
capsomeres.

9. Single/Double - stranded DNA, nonenveloped viruses
• Parvovirus
• Fifths Disease
• Hepatitis B
• Hepatitis C
Tumors, Cancers,
Warts
• Smallpox
• Cowpox
• Herpes simplex cold sores
• Genital herpes
• Kaposi’s sarcoma
Common cold

10. SS or DS RNA, +/- strand, enveloped/nonenveloped
Polio virus
Rhinovirus (colds)
Hepatitis A virus
Hepatitis E virus
Norwalk gastroenteritis
Respiratory infections
Yellow fever,
Dengue, West Nile,
Hepatitis C virus
Rabies virus Ebola and Marburg
viruses
Mumps
Hepatitis D virus,
virulent Influenza
Hanta virus Lassa fever Colorado tick fever

11. Structure of viruses

12. Symmetries of viruses.
1. Icosahedral Symmetry (spherical viruses)
2. Helical symmetry (rod shaped)
3. Complex symmetry

13. Icosahedral Symmetry
• Spherical viruses
• It is a regular polyhedron with 12 vertices, 20
triangular faces and 30 edges.
• Faces – equilateral triangles
• Ex. – Poliovirus and Adenovirus.

14. Helical symmetry
• Rod shaped
• Its NA is covered by a capsid containing capsomeres arranged in
regular helix.
• Ex. – Measles, Mums, Influenza, Rabies virus and TMV.

15. Complex symmetry
A. Ex. - Poxviruses
• They consist of many layers of proteins and
lipoproteins.
• They are brick shaped.
B. Ex. - Bacteriophages
• Binal symmetry
• They have icosahedral head attached to
helical tail.

16. Bacteriophage

17. Nucleic acid of viruses
• They have only one type of nucleic acid.
• Viruses have either DNA or RNA never both.
• NA may be single or double stranded.
• RNA may be single or double stranded
• DNA may be single or double stranded.

18. Nucleic acid of viruses
Nucleic
acid
Examples of viruses
ssRNA Polio, Influenza virus, TMV
dsRNA Reovirus (ex. Rotavirus)
ssDNA Parvovirus
dsDNA Poxvirus

19. Nucleic acid of viruses
• NA may be circular or linear.
• Proportion of NA in viruses varies from 1 % -
(Influenza virus) to 50 % (certain bacteriophages)
• No. of genes in viruses vary from 3 - 4 (picorna virus)
to several hundred (poxviruses)
• All viruses are haploid except retroviruses are diploid.
(Contain 2 identical ssRNA)
• Some viruses have segmented NA (Influenza virus – 8
segments)

20. • RNA viruses:
• RNA positive strand - Picorna virus
• RNA negative strand – myxovirus

21. Envelope
• Some viruses have envelope around capsid.
• Envelope: lipoprotein
• Lipid: derived from host cell membrane
• Protein: virus coded
• Glycoprotein projections may be present on surface
of envelope
• Ex. - Influenza virus: Hemagglutination
prickles (spike like) and neuraminidase
(knob like )

22. • Enveloped viruses: sensitive to lipid solvents – ether, chloroform,
alcohol
• Examples: Influenza, HIV, herpes simplex virus, corona virus

23. If opportunity doesn't
knock, build a door.
Milton Berle

24. Bacteriophage
Lecture II

25. Bacteriophage
• These are viruses that infect bacteria. (Bacteria eater)
• Discovered by Twort and d’Herelle in 1917.
• There two main types of Bacteriophages.
• Virulent or Lytic bacteriophages
• Avirulent or Temperate bacteriophages

26. Bacteriophage

27. Bacteriophage
• Bacteriophages have binal symmetry.
• They have elongated polyhedral (Icosahedral) head.
• Head is attached to tail (Helical) by collar.
• Head encloses DNA.

28. Bacteriophage
• Tail has inner hard core tube which is covered by
contractile sheath.
• Contractile sheath contain 24 protein rings.
• At the end of tail base plate is present.
• Base plate is hexagonal.
• Tail fibers and tail pins are attached to 6 corners of
base plate.

29. Effect of physical and chemical agents
• Viruses are sensitive to physical and chemical agents
• They are easily killed by heat: 60oC for 30min
• Viruses are stored at: – 40oC to -70oC
• They are killed by – hydrogen peroxide,
formaldehyde, chlorine, iodine, ethylene oxide.
• Enveloped viruses are disrupted by lipid solvents
• Antibiotics have no effect on viruses

30. Gratitude is the fairest
blossom which springs from
the soul.
Henry Ward Beecher