The document discusses virus replication, detailing the mechanisms of bacteriophage multiplication through the lytic and lysogenic cycles. It covers the steps of the lytic cycle, including attachment, penetration, biosynthesis, maturation, and release. Additionally, it explains animal virus replication processes and highlights the differences in replication locations for DNA and RNA viruses.

1. UNIT III
3.1 Virus replication
Presented by:
Mohammad Abuzar(M. Pharm)
Assistant Professor School of
Pharmacy AIKTC, New Panvel.

2. CONTENTS
2
Bacteriophage multiplication
Lytic cycle
Summary
References
Introduction
Viral Multiplication

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INTRODUCTION

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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

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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
Bacteriophage infecting E. coli

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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

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Phage adsorption and DNA injection
Assembly of bacteriophage

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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

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Entry of enveloped animal virus
Entry of enveloped virus by endocytosis

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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

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Release of viruses by Budding

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Replication of Animal Virus

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Multiplication of Animal cells

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Multiplication of DNA containing Virus

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Biosynthesis of RNA Virus

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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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1. W.B. Hugo and A.D. Russel: Pharmaceutical Microbiology, Blackwell Scientific publications, Oxford London.
2. Prescott and Dunn., Industrial Microbiology, 4th edition, CBS Publishers & Distributors, Delhi.
3. Pelczar, Chan Kreig , Microbiology, Tata McGraw Hill edn.
4. Malcolm Harris, Balliere Tindall and Cox: Pharmaceutical Microbiology.
5. Rose: Industrial Microbiology.
6. Probisher , Hinsdill et al: Fundamentals of Microbiology, 9th ed. Japan
7. Cooper and Gunn’s: Tutorial Pharmacy, CBS Publisher and Distribution.
8. Peppler : Microbial Technology.
9. I.P., B.P., U.S.P.- latest editions.
10. Ananthnarayan : Text Book of Microbiology, Orient-Longman, Chennai
11. Edward: Fundamentals of Microbiology.
12. N.K.Jain: Pharmaceutical Microbiology, Vallabh Prakashan, Delhi
REFERENCES

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