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