Viruses are acellular, Lecture notes of Microbiology

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VIRUSES- MCB

MCB – MS CHOLA

VIRUSES

Virus is a Latin word meaning poison.

• They are ultramicroscopic particles containing RNA or DNA, which replicate inside other living cells,

Viruses are not cellular and

therefore are classified as neither prokaryotes nor

eukaryotes. Viruses are

obligate intracellular parasites of cellular organisms.

Complete virus particles, are called virions.

• Virions are very small and simple in structure

CHARACTERISTIC

PROPERTIES

Smallest infectious agent

• Obligate intracellular parasites due to lack of enzymes and so depend on the synthetic machinery of host cell

They possess either DNA or RNA – never both.

• The nucleic acid is enclosed in a protein shell
• Do not possess cellular organization

They depend on the ribosomes, enzymes and metabolites of the host cell for protein and nucleic acid production.

Fail to grow on artificial media

• Sensitive to interferon.
• Unaffected by antibiotics

Structure (morphology )

• Viruses are composed of nucleic acids and proteins.
• The genome stores all vital information required by the virus for its replication

The genome is surrounded by a shell or coat made of proteins called capsid

• The genome and capsid are collectively designated as nucleocapsid

Virus

• Nucleic acid co capsid Lipoprotein envelope

• Viruses are classified by the following characteristics:
• Type of genetic material (either DNA or RNA)
• Shape of the capsid
• Number of capsomeres
• Size of capsid

Categories of viruses According to genetic material

• The genetic material of most viruses is either double- stranded DNA or single- stranded RNA.

According to shapes

• The shapes varies in different groups of viruses most animal viruses are spherical, some are irregular and pleomorphic