medicale microbiolojy

Definition of viruses
microscopic particles that can replicate only within a living cell, so widely considered not to be themselves truly living , and not possible to destroy directly without also destroying the host cells. For those that cause human diseases, antiviral drug treatment is limited (antibiotics have no effect) but vaccination can provide immunity and in the second half of the 20th century this eradicated smallpox worldwide and much reduced the incidence of poliomyelitis. Viral conditions include colds, influenza, chickenpox, measles, hepatitis and herpes of different types (e.g. cold sores, shingles). See also human immunodeficiency virus (HIV).
General Properties of Viruses
. Nucleic acid -contains 3-400 genes 1-

Deoxyribonucleic Acid (DNA) -unique features
Single and/or double stranded-
Glycosylated and/or methylated-
Gaps present in double stranded molecule-
Circular or linear-
Bound protein molecules-
Unique purine and/or pyrimidine bases present-
Ribonucleotides present-
Ribonucleic Acid (RNA) - Unique features
Single or double stranded-
Segmented or unsegmented-
Bound protein molecules-
Unique purine and/or pyrimidine bases present-
Folding pattern-

2- Capsid -The capsid accounts for most of the virion mass. It is the protein coat of the virus. It is a complex and highly
organized entity which gives form to the virus. Subunits called protomeres aggregate to form capsomeres which in turn aggregate to form the capsid.
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. 3- Envelope -this is an amorphous structure composed of lipid, protein and carbohydrate which lies to the outside of the capsid It contains a mosaic of antigens from the host and the virus. A naked virus is one without an envelope.


4- Spikes. These are glycoprotein projections which have enzymatic and/or adsorption and/or hemagglutinating activity. They arise from the envelope and are highly antigenic.