Virus replication
Contents
• Life cycle of virus
• Lytic cycle
• Lysogenic cycle
• Life cycle of animal virus
• Replication of DNA virus
• Replication of RNA virus
Intended
Learning objectives
At the end of this lecture, student will be able to:
• Describe the lytic and lysogenic life cycle of a virus
• Differentiate between the lytic cycle of a bacteriophage
and animal virus
• Explain the multiplication of DNA and RNA virus
Viral
multiplication
• For a virus to multiply, it must invade a host cell and
take over the host’s metabolic machinery.
• A single virion can give rise to several or even thousands
of similar viruses in a single host cell. This process can drastically change
the host cell and usually causes its death.
• In a few viral infections, cells survive and continue to
produce viruses indefinitely.
A viral one-step
growth curve – No new infective virions are found in a culture until after
biosynthesis and maturation have taken place
Multiplication
of Bacteriophages
Bacteriophages can multiply by two alternative mechanisms:
• The lytic cycle –
ends with the lysis and death of the host cell
• The lysogenic cycle
– the host cell remains alive in the lysogenic cycle
Lytic cycle
of bacteriophage
1. Attachment
2. Penetration
3. Biosynthesis –
Synthesis of Phage Nucleic Acids and Proteins
4. Maturation – The
Assembly of Phage Particles
5. Release of Phage
Particles
Replication
of animal virus
1. Adsorption of
Virions
– Through a random collision of the virion with a plasma
membrane receptor site protein, frequently a glycoprotein
2. Penetration
Entry of naked animal
virus
Entry of enveloped
animal virus
Entry of enveloped
virus by endocytosis
3. Uncoating
• The removal of the capsid and release of viral nucleic
acid
4. Replication and
transcription of DNA
5. Synthesis and
Assembly of Virus Capsids
6. Virion Release
• Naked virions appear to be released most often by host
cell lysis.
• Enveloped virus – budding
Release of virus by
budding
Summary
• Virus can multiple by lytic or lysogenic cycle
• Steps in lytic cycle – attachment, penetration,
biosynthesis, assembly and release
• Lysogeny involves the formation of a prophage
• DNA virus replicates in nucleus
• RNA virus replicates in cytoplasm
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