Name: how virus shapes help infection
Uploaded: 2019-03-11T09:21:23.000Z
Duration: 56 s
Channel: JoVE

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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 Structure

Although viruses come in a wide variety of shapes and sizes, several structural features are consistent.

A completely mature virus particle, a virion, contains a core, the total genetic content, or genome, with either DNA or RNA, surrounded by a protective coat, the capsid, which is composed of one or more different protein subunits called capsomeres, that dictate their overall size.

Collectively the protein coat and nucleic acid genome form the nucleocapsid.&nbsp;Here, the virus is not enveloped in a lipid covering, so the nucleocapsid and virion are the same thing. Beyond these structures, viruses can differ, but their main function is to deliver genetic material into a host cell for viral replication.

viral structure

Viruses are extraordinarily diverse in shape and size, but they all have several structural features in common. All viruses have a core that contains a DNA- or RNA-based genome. The core is surrounded by a protective coat of proteins called the capsid. The capsid is composed of subunits called capsomeres. The capsid and genome-containing core are together known as the nucleocapsid.

<h4>Structural Classes of Viruses</h4>

Many criteria are used to classify viruses, including capsid design. Most viruses have icosahedral or helical capsids, although some viruses have developed more complex capsid structures. The icosahedral shape is a 20-sided, quasi-spherical structure. Rhinovirus, the virus that causes the common cold, is icosahedral. Helical (i.e., filamentous or rod-shaped) capsids are thin and linear, resembling cylinders. The nucleic acid genome fits inside the grooves of the helical capsid. Tobacco mosaic virus, a plant pathogen, is a classic example of a helical virus. Some viruses have capsids that are enclosed by an envelope of lipids and proteins outside of the capsid. This viral envelope is not produced by the virus but is acquired from the host&rsquo;s cell. These envelope molecules protect the virus and mediate interactions with the host&rsquo;s cells.

<h4>Viral Structure Is Critical for Infection and Immunity</h4>

The viral capsid not only protects the virus&rsquo;s genome, but it also plays a critical role in interactions with host cells. For instance, capsid proteins enable infection by recognizing and binding to specific cell membrane proteins on the host cell. Capsid proteins also play an important role in uncoating the viral genome to enable replication inside the host.

Although the proteins and lipids of the capsid and envelope enable infections, these same molecules are unique to viruses and can, therefore, be used by the hosts&rsquo;s immune system to detect the presence of a virus. Such elicitors of an immune response are generally known as microbe-associated molecular patterns (MAMPs). In plants, MAMPs elicit a cascade of immune responses that can both mitigate the current infection and prepare the plant for a more robust immune response in the event that it becomes infected by a similar pathogen in the future. MAMPs also induce innate immune responses in humans, including inflammation and the production of antimicrobial proteins. Some vaccines take advantage of the body&rsquo;s ability to recognize MAMPs in order to confer immunity to specific viral pathogens.

Viruses are extraordinarily diverse in shape and size, but they all have several structural features in common. All viruses have a core that contains a ...

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KEY TERMS AND CONCEPTS

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 more complex structures. An icosahedral capsid is a 20-sided, quasi-spherical shape. Rhinovirus, which causes the common cold, is an example. A helical capsid is thin and linear, with a rod-like or filament-like shape. Its nucleic acid genome fits inside the grooves of the capsid. Tobacco mosaic virus, a plant pathogen, is a classic helical virus.

Some viruses also have an envelope outside the capsid. This envelope contains lipids and proteins. The virus does not make this envelope itself. It acquires it from the host cell. These envelope molecules help protect the virus and support interactions with host cells.

Viral structure is important for infection. Capsid proteins can recognize and bind to specific proteins on the host cell membrane. They also help uncoat the viral genome so replication can begin inside the host. The same proteins and lipids that help infection can also act as unique markers for the immune system. These markers are called microbe-associated molecular patterns, or MAMPs. In plants, MAMPs can trigger immune responses that reduce the current infection and prepare the plant for future attacks by a similar pathogen. In humans, MAMPs can also activate innate immune responses such as inflammation and the production of antimicrobial proteins. Some vaccines use the immune system's response to MAMPs to build protection against specific viral pathogens.

How Virus Shapes Help Infection

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.

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 recombination

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...

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 virus structure, capsids, envelopes, and MAMPs help viruses infect cells and trigger immune responses in plants and humans.

How Virus Shapes Help Infection | JoVE K12

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How Virus Shapes Help Infection

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