Learn How Virus Replication Occurs

Influenza Virus Particle
This image shows an influenza virus particle. CDC/Frederick Murphy

Viruses are intracellular obligate parasites, which means that they cannot replicate or express their genes without the help of a living cell. A single virus particle (virion) is in and of itself essentially inert. It lacks needed components that cells have to reproduce. When a virus infects a cell, it marshals the cell's ribosomes, enzymes and much of the cellular machinery to replicate. Unlike what we have seen in cellular replication processes such as mitosis and meiosis, viral replication produces many progeny, that when complete, leave the host cell to infect other cells in the organism.

Viral Genetic Material

Viruses may contain double-stranded DNA, double-stranded RNA, single-stranded DNA or single-stranded RNA. The type of genetic material found in a particular virus depends on the nature and function of the specific virus. The exact nature of what happens after a host is infected varies depending on the nature of the virus. The process for double-stranded DNA, single-stranded DNA, double-stranded RNA and single-stranded RNA viral replication will differ. For example, double-stranded DNA viruses typically must enter the host cell's nucleus before they can replicate. Single-stranded RNA viruses however, replicate mainly in the host cell's cytoplasm.

Once a virus infects its host and the viral progeny components are produced by the host's cellular machinery, the assembly of the viral capsid is a non-enzymatic process. It is usually spontaneous. Viruses typically can only infect a limited number of hosts (also known as host range). The "lock and key" mechanism is the most common explanation for this range. Certain proteins on the virus particle must fit certain receptor sites on the particular host's cell surface.

How Viruses Infect Cells

The basic process of viral infection and virus replication occurs in 6 main steps.

  1. Adsorption - virus binds to the host cell.
  2. Penetration - virus injects its genome into host cell.
  3. Viral Genome Replication - viral genome replicates using the host's cellular machinery.
  4. Assembly - viral components and enzymes are produced and begin to assemble.
  5. Maturation - viral components assemble and viruses fully develop.
  6. Release - newly produced viruses are expelled from the host cell.

Viruses may infect any type of cell including animal cellsplant cells, and bacterial cells. To view an example of the process of viral infection and virus replication, see Virus Replication: Bacteriophage. You will discover how a bacteriophage, a virus that infects bacteria, replicates after infecting a bacterial cell.

01
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Virus Replication: Adsorption

Bacteriophage Infecting a Bacterial Cell-1
Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 1: Adsorption
A bacteriophage binds to the cell wall of a bacterial cell.

02
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Virus Replication: Penetration

Bacteriophage Infecting a Bacterial Cell - 2
Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 2: Penetration
The bacteriophage injects its genetic material into the bacterium.

03
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Virus Replication: Replication

Bacteriophage Infecting a Bacterial Cell - 3
Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 3: Viral Genome Replication
The bacteriophage genome replicates using the bacterium's cellular components.

04
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Virus Replication: Assembly

Bacteriophage Infecting a Bacterial Cell - 4
Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 4: Assembly
Bacteriophage components and enzymes are produced and begin to assemble.

05
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Virus Replication: Maturation

Bacteriophage Infecting a Bacterial Cell - 5
Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 5: Maturation
Bacteriophage components assemble and phages fully develop.

06
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Virus Replication: Release

Bacteriophage Infecting a Bacterial Cell - 6
Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 6: Release
A bacteriophage enzyme breaks down the bacterial cell wall causing the bacterium to split open.

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Your Citation
Bailey, Regina. "Learn How Virus Replication Occurs." ThoughtCo, Apr. 5, 2023, thoughtco.com/virus-replication-373889. Bailey, Regina. (2023, April 5). Learn How Virus Replication Occurs. Retrieved from https://www.thoughtco.com/virus-replication-373889 Bailey, Regina. "Learn How Virus Replication Occurs." ThoughtCo. https://www.thoughtco.com/virus-replication-373889 (accessed March 28, 2024).