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

- [Narratore] Anche se
i virus si presentano

in un'ampia varietà

di forme e dimensioni,

diverse caratteristiche
strutturali sono ricorrenti.

Una particella virale
completamente matura, un virione,

contiene un nucleo, il contenuto
genetico totale o genoma,

con DNA o RNA

circondato da un rivestimento
protettivo, il capside,

che è composto da una o più
sottounità proteiche diverse

chiamate capsomeri

che dettano le loro
dimensioni complessive.

Collettivamente,

il rivestimento proteico e
il genoma dell'acido nucleico

formano il nucleocapside.

Qui il virus non è avvolto
in una copertura lipidica,

quindi il nucleocapside e il
virione sono la stessa cosa.

Al di là di queste strutture,

i virus possono essere diversi,

ma la loro funzione principale

è quella di fornire materiale genetico

in una cellula ospite per
la replicazione virale.

Calil, Iara P. e Elizabeth P. B. Fontes. "Immunità delle piante contro i virus: recettori immunitari antivirali in primo piano." Annali di botanica 119, n. 5 (marzo 2017): 711–23. [<a href="https://doi.org/10.1093/aob/mcw200" target="__blank">Sorgente</a>]

struttura dei virus

I virus sono straordinariamente diversi per forma e dimensioni, ma tutti hanno diverse caratteristiche strutturali in comune. Tutti i virus hanno un nucleo che contiene un genoma basato sul DNA o sull'RNA. Il nucleo è circondato da un strato protettivo di proteine chiamato capside. Il capside è composto da sottounità chiamate capsomeri.. Il capside e il nucleo contenente genoma sono insieme noti come nucleocapside.

<h4>Classi strutturali di virus</h4>

Molti criteri vengono utilizzati per classificare i virus, inclusa la progettazione del capside. La maggior parte dei virus hanno capsidi icosaedri o elicoidali, anche se alcuni virus hanno sviluppato strutture di capside più complesse. La forma icosaedrica è una struttura quasi sferica a 20 lati. Il rinovirus, il virus che causa il raffreddore comune, è icosaedro. I capsidi elichi (cioè filamentosi o a forma di asta) sono sottili e lineari, simili a cilindri. Il genoma dell'acido nucleico si inserisce all'interno delle scanalature del capside elicoidale. Il virus del mosaico di tabacco, un agente patogeno vegetale, è un classico esempio di virus elicoidale. Alcuni virus hanno capsidi che sono racchiusi da un involucro di lipidi e proteine al di fuori del capside. Questa busta virale non è prodotta dal virus, ma viene acquisita dalla cellula dell'ospite. Queste molecole di busta proteggono il virus e mediano le interazioni con le cellule dell'ospite.

<h4>La struttura virale è fondamentale per l'infezione e l'immunità</h4>

Il capside virale non solo protegge il genoma del virus, ma svolge anche un ruolo fondamentale nelle interazioni con le cellule ospiti. Ad esempio, le proteine del capside consentono l'infezione riconoscendo e legandosi a specifiche proteine della membrana cellulare sulla cellula ospite. Anche le proteine di capside svolgono un ruolo importante nell'uncoating del genoma virale per consentire la replicazione all'interno dell'ospite.

Anche se le proteine e i lipidi del capside e dell'involucro consentono infezioni, queste stesse molecole sono uniche per i virus e possono quindi essere utilizzate dal sistema immunitario degli ospiti per rilevare la presenza di un virus. Tali elicitori di una risposta immunitaria sono generalmente noti come modelli molecolari associati ai microbi (MAMP). Nelle piante, i MAMP suscitano una cascata di risposte immunitarie che possono sia mitigare l'infezione attuale e preparare la pianta per una risposta immunitaria più robusta nel caso in cui venga infettata da un agente patogeno simile in futuro. I MAC inducono anche risposte immunitarie innate nell'uomo, tra cui l'infiammazione e la produzione di proteine antimicrobiche. Alcuni vaccini sfruttano la capacità del corpo di riconoscere i MAMP al fine di conferire l'immunità a specifici patogeni virali.

Struttura dei virus

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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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.

viral structure

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...

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

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How Virus Shapes Help Infection

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