Virus Structure(Genome)

LECTURE 5:

Viro100: Virology3 Credit hoursNUST Centre of Virology & Immunology

Capsid

Viral core

Envelope

• Out side their host cells, viruses survive as virus particles, also known as virions

• The virion is a gene delivery system; – it contains the virus genome,

• and its functions are – to protect the genome and – to aid its entry into a host cell, – where it can be replicated and packaged into new

virions

Genome

Gapped dsDNA

DNA

dsDNA ssDNA Gapped dsDNA

RNA

dsRNA ss (+) RNA Single s (-) RNA

Classes of viral genomes

The only RNA genomes on the planet today are viral genomes

ss (+) RNA with DNA intermediate

Topology of viral genomes

• It interesting to note that most– fungal viruses have dsRNA genomes, – most plant viruses have ssRNA genomes – and most prokaryotic viruses have dsDNA genomes.

The structure and composition of the genome is a reflection of the method of replication and packaging

What information is encoded in a viral genome

• Gene products and regulatory signals required for:– Replication of the viral genome– Assembly and packaging of the genome– Regulation and timing of the replication cycle– Modulation of host defense system– Spread to other cells and hosts

Virus infectionEpidermal

cells

Mesophyll cells

Bundle sheath cells

PhloemParenchyma

Companion cells

Phloem

Other host plants

Replication

Plant-to-plantmovement

Cell-to-cellmovement

Systemic

movement

Stages of viral infection cycle

Segmented genomes

• Most virus genomes consist of a single molecule of nucleic acid

• Genes of some viruses are encoded in two or more nucleic acid molecules

• The possession of a segmented genome provides a virus with the possibility of new gene combinations, and hence a potential for more rapid evolution

Repeat sequences

Secondary and tertiary structure• Genome encode the virus

proteins• Signals for the control of gene

expression• In ssDNA complementary

sequences may base pair through G–C and A–T hydrogen bonding

• In some ssRNAs intramolecular base pairing results in structures known as pseudoknots

Thank You!

1stAssignment:

Epidemiological profile of Viral diseases in Pakistan