Viral Replication Cycles

Viral replication proceeds through an ordered sequence of steps in which a virus commandeers a host cell to make and release new virus particles.

Definition

A viral replication cycle is the series of events by which a virus enters a host cell, directs the synthesis of new viral components, and produces progeny virions.

Scope

This topic covers the common stages of viral replication, namely attachment, penetration, uncoating, genome replication and gene expression, assembly, and release; the distinct replication strategies of DNA, RNA, and retroviruses; the role of reverse transcription; and the difference between lytic release and budding. It treats replication as the central process that defines viral biology.

Core questions

• What steps make up a viral replication cycle?
• How do replication strategies differ among DNA, RNA, and retroviruses?
• What is the role of reverse transcription in retroviruses?
• How are new virus particles released from the cell?

Key concepts

• Attachment and entry
• Uncoating
• Genome replication and gene expression
• Reverse transcription in retroviruses
• Assembly and release

Key theories

Genome-dependent replication strategies

The pathway a virus uses to express and replicate its genome and to generate messenger RNA depends on its genome type, so different classes of viruses follow distinct but predictable replication routes.

Mechanisms

A virus first attaches to specific receptors on a susceptible cell, then enters and releases its genome. Depending on the genome type, the virus produces messenger RNA and replicates its genome using viral and host enzymes; retroviruses reverse-transcribe their RNA into DNA that integrates into the host genome. New genomes and proteins are assembled into virions, which are released by lysis of the cell or by budding through a membrane.

Clinical relevance

Steps in the replication cycle are the targets of antiviral drugs, which may block attachment, genome replication, or maturation, and understanding replication strategies is essential for developing vaccines and antivirals and for interpreting how viruses cause disease.

History

The discovery of reverse transcriptase by David Baltimore and Howard Temin in 1970 revealed that retroviruses copy RNA into DNA, overturning the assumption that genetic information flows only from DNA to RNA and clarifying a distinctive viral replication strategy.

Key figures

• David Baltimore
• Howard Temin

Seminal works

• baltimore1971
• madigan2018

Frequently asked questions

Why do different viruses replicate in different ways?

A virus's replication strategy is shaped by its genome. Whether the genome is DNA or RNA, single- or double-stranded, determines how the virus must produce messenger RNA and copy its genome, leading to distinct replication routes among virus groups.