Name: how viruses swap genes and spread
Uploaded: 2019-03-11T09:21:24.000Z
Duration: 57 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

from-molecules-to-organisms-structures-and-processes

From Molecules To Organisms: Structures And Processes

HS-LS1-8

Viral Recombination

Some cells may be infected by two different strains of a virus at the same time causing a mix-up of both genetic sequences in a process called viral recombination. More specifically, after the virus has entered the cell&#39;s cytoplasm, they disassemble and begin to replicate their genomes.

Similar regions of each genome can pair together and exchange pieces, reconnecting the strands.&nbsp;Alternatively, the viruses can swap some of their segments in a process called reassortment, in which new viruses made inside the cell can have a mixture of the strains, such as half of their segments from strain one and the other half from strain two.

These newly formed viruses have now evolved from the two original viruses forming populations that may continue to change over time.

viral recombination

Cells are sometimes infected by more than one virus at once. When two viruses disassemble to expose their genomes for replication in the same cell, similar regions of their genomes can pair together and exchange sequences in a process called recombination. Alternatively, viruses with segmented genomes can swap segments in a process called reassortment.

<h4>Viral Recombination Can Create New Diseases</h4>

Some diseases can infect multiple species. For example, pigs can be infected by some human and bird viruses, in addition to the viruses that usually infect pigs. Because viruses can recombine when they co-infect the same cell, pigs can act like &ldquo;mixing vessels&rdquo; that recombine viruses from other species to create new viruses that can sometimes infect humans. This worrisome phenomenon represents a route through which infectious material from other species can enter the human population. Diseases that move from animals to humans are known as zoonoses. Humans can be highly susceptible to such viruses because we have no history of exposure that would have generated immunity.

Influenza A is a prime example of the &ldquo;mixing vessel&rdquo; theory of viral disease. Research has demonstrated that pig, bird, and human influenza A viruses have reassorted inside pig hosts. These events yielded &ldquo;double reassortant&rdquo; viruses that contained genes from human and bird viruses and &ldquo;triple-reassortant&rdquo; viruses that contained genes from human, bird, and pig viruses. In the Netherlands, a reassortant virus composed of human and bird flu genes was transmitted from pigs to humans.

Cells are sometimes infected by more than one virus at once. When two viruses disassemble to expose their genomes for replication in the same cell, ...

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KEY TERMS AND CONCEPTS

how viruses swap genes and spread

Viral gene swapping can happen when more than one virus infects the same cell. After the viruses break open and expose their genomes for replication, matching regions can pair up and exchange sequences. This process is called recombination. Viruses with segmented genomes can also swap whole segments, which is called reassortment.

These changes can help create new diseases. Some diseases can infect more than one species. Pigs can be infected by some human and bird viruses, along with the viruses that usually infect pigs. When different viruses co-infect the same pig cell, the pig can act as a mixing vessel and help produce new viruses that may infect humans.

This matters because diseases that move from animals to humans are called zoonoses. Humans can be highly susceptible to these viruses because we may not have previous exposure. Without that exposure, we would not have developed immunity. Influenza A is a clear example of the mixing vessel theory. Research has shown that pig, bird, and human influenza A viruses have reassorted inside pig hosts.

Some of those events produced double reassortant viruses with genes from human and bird viruses. Others produced triple-reassortant viruses with genes from human, bird, and pig viruses. In the Netherlands, a reassortant virus made from human and bird flu genes was passed from pigs to humans.

How Viruses Swap Genes and Spread

what are viruses?

How Viruses Infect Cells and Multiply

Viruses infect cells and make new copies by using a host cell’s own machinery. A virus is a tiny infectious particle with an RNA or DNA genome inside a protective protein coat. It cannot reproduce on its own, so it must enter a cell to make more viruses. After infection, the virus sheds its protein coat and uses the host cell to transcribe and translate its genetic material. The cell then assembles many new viral particles. In many cases, these new viruses rupture the host cell and kill it.

viral structure

How Virus Shapes Help Infection

Viruses have specific structures that help them infect host cells and trigger immune responses. Each virus has a core that contains either a DNA-based or RNA-based genome. That core is surrounded by a protective protein coat called the capsid. The capsid is made of smaller subunits called capsomeres. The capsid and the genome-containing core together are called the nucleocapsid. Viruses are often grouped by capsid design. Most viruses have either icosahedral or helical capsids, but some have...

lytic cycle of bacteriophages

How Phages Infect and Burst Bacteria

Bacteriophages, or phages, are viruses that infect bacteria. They have a distinctive head-tail shape. In the lytic cycle, a phage first attaches to the outside of a bacterial cell. Tail proteins bind to specific receptor proteins on the bacterium’s surface. After attachment, the phage tail injects its DNA genome into the bacterial cytoplasm. The phage then uses the bacterium’s cellular machinery to make proteins needed for replication and dispersal. When phage replication is complete, some of...

lysogenic cycle of bacteriophages

Prophage Integration in Bacteria

The lysogenic cycle shows how bacteriophages can infect bacteria without killing the host right away. In this cycle, the phage genome joins the bacterial genome. The integrated phage DNA is called a prophage, and the bacterium copies it each time it replicates. Some prophages can switch back into the lytic cycle. This change can happen after DNA damage or even without an obvious outside trigger. When the prophage is induced, the phage begins making new virus particles again. Prophages can...

retrovirus life cycles

How Retroviruses Replicate in Host Cells

Retroviruses replicate by copying their RNA genome into DNA inside a host cell. After entry, the viral enzyme reverse transcriptase makes a double-stranded DNA copy from the single-stranded RNA genome. The viral DNA is then carried into the nucleus and inserted into the host genome by integrase. Once integrated, the retroviral DNA is transcribed whenever the host genome is transcribed. This produces new viral RNA that can be copied and used again. The new RNA moves into the cytoplasm, where it...

Viral gene swapping can happen when more than one virus infects the same cell. After the viruses break open and expose their genomes for replication, matching regions can pair up and exchange sequences. This process is called recombination. Viruses with segmented genomes can also swap whole segments, which is called reassortment. These changes can help create new diseases. Some diseases can infect more than one species. Pigs can be infected by some human and bird viruses, along with the...

viral mutations

How Virus Mutations Drive Outbreaks

Virus mutations can change how quickly a virus evolves and spreads. A mutation is a change in the sequence of bases in DNA or RNA. Some mutations happen when the genome is copied. They are caused by errors made by polymerase enzymes, which replicate DNA or RNA. RNA viruses often change faster than DNA viruses because RNA polymerase does not proofread its work. That means RNA-based genomes, such as HIV, can gather mutations more quickly. Mutation and recombination give viruses the raw material...

key terms and concepts

Learn how viral recombination and reassortment happen when viruses infect the same cell, and how pigs can help new flu viruses spread to humans.

How Viruses Swap Genes and Spread | JoVE K12

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HS-LS1-4

How Viruses Swap Genes and Spread

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