Introduction to virology
Virus: infectious, obligate intracellular parasite containing genetic material. It must also have nucleic
acid within it – either RNA or DNA, never both.
Virus particles assemble of pre-formed components.
• Genome (RNA or DNA; segmented)
• Capsid (protein)
• Nucleocapsid = capsid+genome
• Envelope (sometimes) – non-enveloped are stronger.
• Glycoproteins
• Exploit metabolism of host cell.
Viruses are classified using the Baltimore classification system. The type of viral nuclei determines
the method of replication and transcription e.g. HIV via reverse transcriptase and integrase as it has
reverse RNA present.
, Viruses vary in size of genome:
Human Virus:
Hepatitis B: 3 kb
HIV: 10 kb
Adenovirus: 35kb
Vaccina: 185kb
CMV 235kb
Capsids and Envelopes:
• Capsid
o Protects nucleic acid
o Must also be easy to disassemble
o Helical (e.g. flu)
o Icosahedral (e.g. Adenovirus)
o Complex (e.g. poxvirus)
• Enveloped
o Surrounded by lipid envelope derived from the host cell
o Contains viral glycoproteins
o Sensitive to drying out
o Will not survive the gut
Generic Virus Replication Cycle:
o There are 2 ways a virus can be released: budding or via lysis of host cell.
o Viruses grow by assembly of pre-formed components e.g. envelope.
Virus: infectious, obligate intracellular parasite containing genetic material. It must also have nucleic
acid within it – either RNA or DNA, never both.
Virus particles assemble of pre-formed components.
• Genome (RNA or DNA; segmented)
• Capsid (protein)
• Nucleocapsid = capsid+genome
• Envelope (sometimes) – non-enveloped are stronger.
• Glycoproteins
• Exploit metabolism of host cell.
Viruses are classified using the Baltimore classification system. The type of viral nuclei determines
the method of replication and transcription e.g. HIV via reverse transcriptase and integrase as it has
reverse RNA present.
, Viruses vary in size of genome:
Human Virus:
Hepatitis B: 3 kb
HIV: 10 kb
Adenovirus: 35kb
Vaccina: 185kb
CMV 235kb
Capsids and Envelopes:
• Capsid
o Protects nucleic acid
o Must also be easy to disassemble
o Helical (e.g. flu)
o Icosahedral (e.g. Adenovirus)
o Complex (e.g. poxvirus)
• Enveloped
o Surrounded by lipid envelope derived from the host cell
o Contains viral glycoproteins
o Sensitive to drying out
o Will not survive the gut
Generic Virus Replication Cycle:
o There are 2 ways a virus can be released: budding or via lysis of host cell.
o Viruses grow by assembly of pre-formed components e.g. envelope.
