Name: how viruses infect cells and multiply
Uploaded: 2019-03-11T09:21:23.000Z
Duration: 50 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

What are Viruses?

- [Narratore] Un virus è
una struttura che porta

il proprio materiale
genomico sotto forma di RNA

o il DNA da invadere e replicare

all'interno di una cellula ospite.

Dopo che un virus si lega
ai recettori di superficie

sulla cellula ospite,

entra e si smonta rapidamente,

decodificando il suo materiale genetico.

Nel caso dei virus del DNA,

il DNA virale dirige

le proteine di replicazione
della cellula ospite

per sintetizzare nuove copie
del genoma virale che sono

poi trascritte e tradotte
in proteine virali.

Infine, l'ospite riassembla
queste componenti virali

in progenie

che permette ad una
singola particella virale

di produrne migliaia che spesso conducono

alla morte della cellula ospite.

Yamauchi, Yohei e Ari Helenius. "Ingresso del virus a colpo d'occhio." J Cell Sci 126, n. 6 (15 marzo 2013): 1289–95. [<a href="https://doi.org/10.1242/jcs.119685" target="__blank">Sorgente</a>]

Lin, Derek M, Britt Koskella e Henry C Lin. "Terapia fagica: un'alternativa agli antibiotici nell'era della resistenza multifarmacologica". World Journal of Gastrointestinal Pharmacology and Therapeutics 8, n. 3 (6 agosto 2017): 162–73. [<a href="https://doi.org/10.4292/wjgpt.v8.i3.162" target="__blank">Sorgente</a>]

Nicaise, Valérie. "Immunità delle colture contro i virus: risultati e sfide future". Frontiers in Plant Science 5 (21 novembre 2014). [<a href="https://doi.org/10.3389/fpls.2014.00660" target="__blank">Sorgente</a>]

cosa sono i virus?

<h4>Panoramica</h4>

Un virus è una particella infettiva microscopica costituita da un genoma di RNA o DNA racchiuso in un guscio proteico. Non è in grado di riprodursi da solo: può fare solo più virus entrando in una cellula e utilizzando i suoi macchinari cellulari. Quando un virus infetta una cellula ospite, rimuove il suo strato proteico e dirige il macchinario dell'ospite per trascrivere e tradurre il suo materiale genetico. La cellula dirottata assembla i componenti replicati in migliaia di progenie virali, che possono rompersi e uccidere la cellula ospite. I nuovi virus poi vanno a infettare più cellule ospiti.

<h4>Perché studiare i virus?</h4>

I virus possono infettare diversi tipi di cellule: batteri, piante e animali. I virus che prendono di mira i batteri, chiamati batteriofagi (o fagi), sono molto abbondanti. La ricerca attuale si concentra sulla terapia del fago per trattare le infezioni batteriche multifarmacoresistenti negli esseri umani. Anche i virus che infettano le piante coltivate sono molto studiati poiché le epidemie portano a enormi perdite di colture ed economiche.

I virus furono scoperti per la prima volta nelXIX secolo, quando una coltura economicamente importante, la pianta del tabacco, fu afflitta da una misteriosa malattia, successivamente identificata come virus del mosaico del tabacco. I virus animali sono di grande importanza sia nella ricerca veterinaria che nella ricerca medica. Inoltre, i virus sono alla base di molte malattie umane, che vanno dal comune raffreddore, varicella, e herpes, alle infezioni più pericolose come febbre gialla, epatite, e vaiolo.

<h4>La struttura di un virus</h4>

I virus sono disponibili in una varietà di forme che sono specializzati nell'attaccare la loro cellula bersaglio. I due componenti principali di tutti i virus sono il genoma virale e il suo mantello proteico protettivo, noto come il capside. Il genoma virale è costituito da RNA o DNA a singolo o doppio filamento, e codifica le proteine che compongono il capside. Insieme, il genoma virale e il capside sono noti come nucleocapside.

Una caratteristica unica di molti virus eucarioti è la presenza di una membrana fosfolipidide, conosciuta come l'involucro che circonda il capside. Questa busta in genere proviene dalle membrane delle cellule ospiti precedentemente infette, ma può anche includere proteine virali (chiamate proteine della busta) ad esso collegate. Infine, alcuni virus animali hanno un gruppo di proteine codificate da virus, il tegumento virale, nello spazio tra la busta e il capside.

<h4>Infezione virale</h4>

Il ciclo di vita virale può essere suddiviso nei cinque passaggi seguenti: allegato, voce, replica, assemblaggio e rilascio. Le proteine sulla superficie del virus lo aiutano a riconoscere specifiche cellule ospiti. Alcuni virus utilizzano queste proteine superficiali per legare i recettori delle cellule ospiti e avviare l'internalizzazione mediante endocitosi, mentre i virus rivestiti di busta possono fondersi direttamente con la membrana cellulare ospite.

Alcuni batteriofagi non entrano nella cellula; iniettano il loro genoma (e gli enzimi virali) nella cellula ospite. Una volta all'interno della cellula, il virus non è rivestito e dirige i macchinari della cellula ospite per trascrivere e tradurre il suo genoma. La cellula ospite imballa le nuove copie del genoma virale in particelle virali per fare la progenie. I virus della progenie possono essere immagazzinati nella cellula ospite prima del rilascio o continuamente estrusi dalla cellula in erba dalla membrana cellulare. Il ciclo di infezione virale è classificato come litico o lisogenico. Nel ciclo litico, i nuovi virus esplodono dalla cellula ospite uccidendola. Nel ciclo lisogeno, il DNA virale viene incorporato nel genoma dell'ospite dove giace domenzato e viene copiato ogni volta che la cellula ospite si replica.

Cosa sono i virus?

Overview

A virus is a microscopic infectious particle that consists of an RNA or DNA genome enclosed in a protein shell. It is not able to reproduce on ...

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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. The released viruses can then infect other cells.

Viruses can attack bacteria, plants, and animals. Viruses that infect bacteria are called bacteriophages, or phages, and they are very abundant. Scientists also study phages as a possible therapy for multidrug-resistant bacterial infections in humans. Plant viruses matter because outbreaks can cause major crop and economic losses.

Animal viruses are important in both veterinary research and medical research. Viruses were first discovered in the 19th century during studies of tobacco plants with a mysterious disease. That disease was later identified as Tobacco mosaic virus. Viruses are also linked to many human illnesses, including the common cold, chickenpox, herpes, yellow fever, hepatitis, and smallpox.

Viruses vary in shape, but they share two main parts: the viral genome and the capsid. The genome can be single-stranded or double-stranded RNA or DNA, and it carries the instructions for making capsid proteins. The genome and capsid together form the nucleocapsid. Many eukaryotic viruses also have an envelope, which is a phospholipid membrane often taken from a host cell. Some animal viruses also contain a tegument, a layer of viral proteins between the envelope and the capsid.

A viral infection usually follows five stages: attachment, entry, replication, assembly, and release. Viral surface proteins help the virus recognize the right host cell. Some viruses bind to host receptors and enter by endocytosis, while enveloped viruses can fuse with the host cell membrane. Some bacteriophages do not enter the cell at all. They inject their genome and viral enzymes into the host cell instead.

Once inside, the virus is uncoated and directs the host cell to copy and read its genetic material. The host cell packages the new genomes into viral particles to form progeny viruses. These progeny may stay in the cell for a time or leave by budding from the cell membrane. Viral infection can be lytic or lysogenic. In the lytic cycle, new viruses burst out and kill the host cell. In the lysogenic cycle, viral DNA becomes part of the host genome, stays dormant, and is copied when the host cell divides.

How Viruses Infect Cells and Multiply

what are viruses?

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 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 viruses enter host cells, use cellular machinery to replicate, and spread through lytic and lysogenic cycles in plants, animals, and bacteria.

How Viruses Infect Cells and Multiply | JoVE K12

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HS-LS1-4

How Viruses Infect Cells and Multiply

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