FIRST DEVELOPMENTS IN VIROLOGY

VII. VIRUSES

 Mandatory intracellular parasites

 They carry incomplete genetic information, do not have the necessary genes for metabolic activities

 Virion cannot grow and divide

 Separate synthesized parts of the cell are brought together to form a virion

 They carry DNA or RNA, but not both

 They can infect new cells after they proliferate in a cell

 Virions have one or more uniform nucleic acids

FIRST DEVELOPMENTS IN VIROLOGY

 1798  Edward Jenner  Pox vaccine

 19th century Pasteur  virus

 1884  Charles Chamberland  bacterial filter

 1892  Dimitri Iwanowski  Tobacco mosaic virus

 1898  Friedrich Loeffler ve Paul Frosch  cattle  foot and mouth disease

 1900  Walter Reed  Yellow fever

 1911  Peyton Rous  chicken  Rous

sarcoma virus  tumor

FIRST DEVELOPMENTS IN VIROLOGY

 1915-17  Frederick W. Tworth ve Felix dHerelle

 bakteriophage

 1933  R. E. Shape  Papilloma virus  cancer in mammalia

 Production of viruses n embryo eggs (1920) and human cell cultures (1949)

 J. F. Enders et al. Produced the first time Poliovirus in this way.

 1935  Wendell M. Stanley  tobacco mosaic virus crystallization

 1940  Ruska  electron microskobe  structure of bakteriophage

 1981  DNA virüs hepatit B  revers transcriptase enzyme

 1983  HIV (Human Immunodeficiency Virus)  AIDS (Acquired immunodeficiency Syndrome =

METHODS USED IN VIROLOGY

Generation of Viruses Animal Viruses:

Embryoned egg

Laboratory animals Cell cultures

Plant Viruses:

In plants or plant tissue (cell and protoplast) cultures

Bacteriophages:

Active bacterial cells developing in liquid or

solid environments

Virus Purification

 Centrifugation

 Precipitation with chemicals

 Denaturation of contaminants

 Enzymatic digestion

Quantification of Viruses

 Determination of the total number of virions

 1. Virions are counted directly in the electron microscope.

 2. Hemagglutination test

 Determination of infective virion

number

Determination of viral structure

 Filtration (size),

 Ultracentrifuge,

 Electrophoresis (nucleic acid and proteins),

 Hybridization (nucleotide sequence),

 Nuclear magnetic resonance (atomic properties of viral molecules),

 Electron microscopy, SEM and TEM, x-ray

diffraction

CLASSIFICATION OF VIRUSES

 familia  viridae Poxviridae

 Subfamilia  virinae Chordopoxvirinae

 Genus  virus Orthopoxvirus

 Species  Vaccinia virus

STRUCTURAL PROPERTIES OF VIRUSES Virion Types:

 Virions with helical capsules: Tobacco Mosaic Virus

 Icyhedral (Polyhedral) capitulated

virions: 20 equilateral triangular faces, at least 3 different proteins in each structure, at least 60 proteins.

 Virions with complex structure: Pox virus and Tailed Bacteriophages

 Enveloped viruses

Viral enzymes

 Polymerase enzymes (RNA polymerase, reverse transcriptase)

 Neuraminidase

 Lysozyme

Virus Genome

 It consists of DNA or RNA.

 Linear, circular or segmented,

 Single strand (ss) or double strand (ds),

 Single-stranded genomes:

 Positive (+) significant, same as nucleotide sequence mRNA

 Negative (-) significant complement of nucleotide sequence mRNA

 Ambisens are grouped into three groups, both - and + significant regions.

Virss Genome

 mRNA 5’..GAC UCG AGC..3’

 +ssRNA  5’..GAC UCG AGC..3’

 -ssRNA  3’..CUG AGC UCG..5’

 +ssDNA  5’..GAC TCG AGC..3’

 -ssDNA  3’..CTG AGC TCG..5’

Genome Sizes of Some Organisms

 Viruses 3.500 (MS2) – 280.000 (CMV) nt

 Parazitic bacteria…….590.000 nt

 Bacteria……….4.700.000 nt (E. coli)

 Yeasts ………...10.600.000 nt

 Human…………6.000.000.000 nt