Virus

Introduction
Classification of virus
Size of virus
Structure of Virus
Morphology of Virus
Effect of Physical and chemical agents on virus.
Life cycle of bacteriophages
Cultivation of viruses

1. VIRUS Prepared by , Mr. Snehal Patel, Assistant Professor, Sumandeep Vidyapeeth , Vadodara, Gujarat, India.

2. Content Introduction Classification of virus Size of virus Structure of Virus Morphology of Virus Effect of Physical and chemical agents on virus. Life cycle of bacteriophages Cultivation of viruses

3. 1. Introduction Viruses are infectious agents so small that they can only be seen by the electron microscope. They are 10 to 100 times smaller than most bacteria. Viruses are incapable of independent growth in artificial media. They can grow only in animal or plant cells or in microorganisms. Thus, viruses are referred to as obligate intracellular parasites. Viruses largely lack metabolic machinery of their own to generate energy or synthesis proteins. They depend on host cell to carry out this vital function.

4. The viral genetic material is either DNA or RNA, but virus does not have both DNA or RNA. Nucleic acid is enclosed in a highly specialized protein coat. The coat protects the genetic material when the virus is outside any host cell and serves as a vehicle for the entry into another specific host cell. The structurally complete, mature and infectious virus is called virion . They multiply by a complex process and not by binary fission. They are unaffected by antibacterial antibiotics.

5. Viral diseases ranges from minor ailments such as common cold to highly fatal diseases such as AIDS or yellow fever. Viruses may cause mumps, rabies, influenza, measles or herpex simplex.

6. 2. Classification of virus According to their pathogenicity on living kingdom. According to their nucleic acid. According to their pathogenicity on different system or organs of human beings. According to the capsid morphology. According to the presence or absence of envelop.

7. 1. According to their pathogenicity on living kingdom. Bacterial virus ( Phagineae ) They have DNA and are called bacteriophages or simply phages. Eg : T 1 to T 4 bacteriophages 2. Plant virus ( phytophagineae ) They have RNA and infect potato, sugarcane, tobacco, cucurbitis and any other higher plant. Eg : Tobacco necrosis virus (TNV) 3. Animal virus ( zoophagineae ) They usually have DNA but may also have RNA and infect man, pigeon, dog, cow, arthropods etc. Eg : Poxvirus, Herpes simplex virus.

8. 2. According to their nucleic acid. 1. Deoxy viruses Viruses contain DNA. Eg : Pox virus, Herpes simplex virus. 2. Ribo viruses Viruses contain RNA. Eg : Enterovirus .

9. 3. According to their pathogenicity on different system or organs of human beings. Neutrotropic viruses Viruses affect nervous system are called neutrotropic viruses. Eg : Polio and Rabies. 2. Dermatotropic viruses Viruses produces skin lesions. Eg : small pox, chicken pox and measles. 3. Pneumatotropic viruses Viruses affect respiratory tract. Eg : Rhinovirus.

10. 4. According to the capsid morphology. Polyhederal ( Icosahedral ) virus Viruses are polygonal in shape. Eg : Polio virus, Adenovirus. Helical (Spiral) virus Viruses are spiral in shape. Eg : Rabies virus

11. 5. According to the presence or absence of envelop. Enveloped Virus Viruses whose capsids are covered by an envelope are known as enveloped virus. Eg : Togavirus . 2. Non-enveloped or Naked Virus Viruses whose capsids are not covered by an envelope are known as non-enveloped or Naked virus. Eg : Microvirus , Adenovirus.

12. Size of viruses Viruses are much smaller than bacteria. As they are too small to be seen under the light microscope, they are called ultramicroscopic. Some of the larger viruses such as pox viruses can be seen under the light microscope when suitable stained. Some of the larger viruses such as pox viruses 300 nm are about the same size of small bacteria ( mycoplasmas ) The smallest viruses ( eg : parvovirus) measure about 20 nm.

13. 4. Structure of Virus Virus is composed of inner core which is surrounded by a coat that protects it from the environment. Viruses are not cellular and therefore do not have nucleus, cytoplasm or cell membrane.

14. Capsid and Envelope

15. Core The core contains nucleic acids. The virus contains only one type of nucleic acid. It may be either DNA or RNA. If virus contain DNA is called Deoxyvirus . If it contains RNA is called Ribovirus . The nucleic acid may be single stranded or double stranded.