This document discusses viruses, including their structure, classification, and discovery. It notes that viruses consist of nucleic acid and a protein coat, and are able to multiply only within host cells. It describes some of the early discoveries of viruses in the late 19th century. It also summarizes different classification systems for viruses, including those based on nucleic acid type, structure, and genome, such as the Baltimore classification system. The document provides an overview of viruses with relevant details on their composition, life cycles, and taxonomic organization.

1. VIROLOGY
DISCOVERY OF VIRUS NOMENCULTURE,
CLASSIFICATION
MUSKAN
M.SC 1ST SEM

2. VIRUS
 Virus that mans poisonous that infect to all other organism.
 Viruses are a unique group of infectious agents that typically consist of nucleic acid
molecules in a protein coat.
 Viruses are too small to be seen by light microscopy.
 Viruses are able to multiply only within the living cells of a host.
 Viruses vary in shape from the simple helical and icosahedral to more complex
structures.
 Viruses range in size from 20 to 300 nm.
 Genes made from DNA or RNA, long molecule that carry genetic information.
 Protein coat that protects the genes, and in some viruses, an envelope of fat.
 They occur in bacteria, algae, protozoa, and higher plant and animals.
 Virus spread in many way:- by vactor, by air droplet nuclei , by body fluid during sex—

3. BASIC KEY POINT OF VIRUS
 Obligate intracellular parasite.
 their simple, acellular organism.
 Do not independently fulfill the characterstic of life.
 Basic str. Consists of a protein coat + nucleic acid(DNA or
RNA) but not both either can be double stranded DNA , single
stranded DNA, double stranded RNA, single stranded RNA.
 Virus are very specific to which host for own multiplication ,
protein synthesis, bcz that have no ability to introducing to
them self.

4. VIRUS STRUCTURE
 Virus are consists of protein coat ( capsid) and nucleic acid .
 These additional layers may be very complex and contain carbohydrates, lipids and and
additional protein also known as envelop.
CAPSID:-- capsid are made up of capsomere unit
.Capsid are provided the arrengment in different different shape of size in virus.
 Helicle structure
 Complex structure
 isohedral structure

5. LIFE CYCLE OF VIRUS
 Virus are life cycle completed in two phages
1. Lytic cycle 2. lysogenic cycle

6. DISCOVERY OF VIRUS
 In 1884 the French microbiologist Charles Chamberland invented a filter, known today as the
Chamberland filter or Chamberland-Pasteur filter, that has pores smaller than bacteria. Thus
he could pass a solution containing bacteria through the filter and completely remove them
from the solution.
 In the early 1890s the Russian biologist Dmitri Ivanovsky used this filter to study what became
known as the tobacco mosaic virus. His experiments showed that extracts from the crushed
leaves of infected tobacco plants remain infectious after filtration.
 In 1899 the Duch microbiologist Martinus Beijerinck observed that the agent multiplied only
in dividing cells. Having failed to demonstrate its particulate nature he called it a contagium
vivum fluidum a soluble living germ.
 In the early 20th century the English bacteriologist Frederick Twort discovered viruses that
infect bacteria.
 With the invention of the electron microscope in 1931 by German Engineers Ernst Ruska and
Max Knoll came to the first images of viruses.
 In 1935, American biochemist and virologist Wendell Meredith Stanley examine the tobacco
mosaic virus and found it to be mostly made from protein.

7. NOMENCULTURE OF VIRUS
 Various approaches, (do not obey the binomial nomenclature) derived from:
 1. Named after the diseases e g. Measles virus, smallpox virus
 2. Name after the places where the disease first reported e g. Newcastle
disease virus, Ebola virus, Norwalk virus,
 3. Host and signs of disease e g. Tobacco mosaic virus, cauliflower mosaic virus.
 4. Latin and Greek words e g. Coronaviridae – “crown” Parvoviridae – “small”
 5. Virus discovers e g. Epstein-Barr virus
 6. How they were originally thought to be contracted eg. dengue virus (“evil
spirit”), influenza virus (the “influence” of bad air)
 7. Combinations of the above e g. Rous Sarcoma virus

8. NOMENCULTURE OF VIRUS
 Till 1950, viruses were named based on the diseases they caused or on the
place of their isolation. They were grouped according to assumed tropisms or
affinity to different systems or organs of the body.
 Thus human viruses were classified as :
 Dermotropic-Viruses those producing skin lesions (smallpox, chicken pox,
measels).
 Neurotropic – Viruses those affecting the nervous system (Poliomyelitis,
rabies).
 Pneumotropic- Viruses those affecting the respiratory tract (influenza, common
cold).
 Viscerotropic- Viruses those affecting visceral organs (yellow fever, hepatitis).

9. CLASSIFICATION OF VIRUS
 Viruses are not classified as members of the kingdoms.
 Viruses do not obey the biological taxonomy.
 THE CLASSIFICATION OF VIRUS IS GENERALLY BASED ON:-
 CLASSICAL
 GENOMIC
 SEROLOGY
 Holmes (1948) followed the Linnean system of binomial nomenclature and put the
viruses into an order virales and three suborders:
(i) Phaginae: Viruses attacking on bacteria.
(ii) Phytophagine: Viruses attacking on plants.
(iii) Zoophaginae: Viruses attacking on animals.

10. LHT SYSTEM OF CLASSIFICATION
 In 1962, A. Lwoff, R. Horne and P. Tournier proposed a system of
classification of viruses which is commonly referred to as LHT system of
classification. It was adopted by the provisional committee on
Nomenclature of viruses (PNCV) formed by the International Association of
Microbiological society. The LHT system of classification is based on:
 (i) The nature of nucleic acid (DNA or RNA)
 (ii) Symmetry of viral particle ( helical, icosahedral, cubic, cubic tailed)
 (iii) Presence or absence of envelope
 (iv) Diameter of capsid
 (v) Number of capsomers forming the capsid.

11. BALTIMORE CLASSIFICATION
 The Baltimore classification (2008) of viruses is based on genome type and
mode of replication and transcription.
 Suggested by David Baltimore – Seven Baltimore classes. The Nobel prize
winning biologist David Baltimore devised the Baltimore classification system.
 The ICTV classification system is used in conjugation with the Baltimore
classification system in modern virus classification.
 Major groups of viruses are distinguished first by their nucleic acid content as
either DNA or RNA.
 RNA and DNA viruses can be single-stranded (ssRNA, ssDNA) or double
stranded (dsRNA, ssDNA) and may or may not usecan be single-stranded
(ssRNA, ssDNA) or double may or may not use reverse transcriptase. ssRNA
may be either (+) sense or (-) antisense.

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