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

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High School

Life Sciences

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

From Molecules To Organisms: Structures And Processes

HS-LS1-8

What are Viruses?

Um vírus é uma estrutura que carrega seu próprio material genómico na forma de RNA ou DNA para invadir e replicar dentro de uma célula hospedeira. Depois que um vírus se liga à recetores de superfície na célula hospedeira, ele entra e desmonta rapidamente, descodificando seu material genético. No caso dos vírus de DNA, o DNA viral direciona as proteínas de replicação das células hospedeiras para sintetizar novas cópias do genoma viral que são então transcritas e traduzidas em proteínas virais.Finalmente, o hospedeiro remonta estes componentes virais em progénie, permitindo que uma única partícula de vírus produza outras milhares, frequentemente levando à morte da célula hospedeira.

Yamauchi, Yohei e Ari Helenius. "Entrada de vírus em resumo." J Cell Sci 126, nº 6 (15 de março de 2013): 1289–95. [<a href="https://doi.org/10.1242/jcs.119685" target="__blank">Fonte</a>]

Lin, Derek M, Britt Koskella e Henry C Lin. "Terapia fágica: uma alternativa aos antibióticos na era da resistência a múltiplos medicamentos." Jornal Mundial de Farmacologia e Terapêutica Gastrointestinal 8, nº 3 (6 de agosto de 2017): 162–73. [<a href="https://doi.org/10.4292/wjgpt.v8.i3.162" target="__blank">Fonte</a>]

Nicaise, Valérie. "Imunidade de culturas contra vírus: resultados e desafios futuros." Fronteiras na ciência das plantas 5 (21 de novembro de 2014). [<a href="https://doi.org/10.3389/fpls.2014.00660" target="__blank">Fonte</a>]

o que são vírus?

<h4>Visão Geral</h4>
 
 Um vírus é uma partícula infecciosa microscópica que contém um genoma de RNA ou DNA fechado em uma cápsula de proteína. Ele não é capaz de se reproduzir por conta própria: só pode produzir mais vírus entrando em uma célula e usando as suas maquinarias celulares. Quando um vírus infecta uma célula hospedeira, ele remove a sua cápsula de proteína e direciona a maquinaria do hospedeiro a transcrever e traduzir o seu material genético. A célula sequestrada monta os componentes replicados em milhares de descendentes virais, que podem romper e matar a célula hospedeira. Os novos vírus passam então a infectar mais células hospedeiras.
 
 <h4>Porquê Estudar Vírus?</h4>
 
 Os vírus podem infectar diferentes tipos de células: bactérias, plantas e animais. Vírus que visam bactérias, chamados bacteriófagos (ou fagos), são muito abundantes. A investigação atual concentra-se na terapia por fagos para tratar infecções por bactérias resistentes a múltiplos fármacos em humanos. Vírus que infectam plantas cultivadas também são altamente estudados, uma vez que epidemias levam a enormes perdas agrícolas e económicas.
 
 Os vírus foram descobertos pela primeira vez no século XIX, quando uma cultura economicamente importante, a planta do tabaco, foi atacada por uma doença misteriosa—mais tarde identificada como vírus do mosaico do tabaco. Os vírus animais são de grande importância tanto na investigação veterinária como na investigação médica. Além disso, os vírus estão por trás de muitas doenças humanas, que vão desde a constipação comum, varicela e herpes, até infecções mais perigosas como febre amarela, hepatite e varíola.
 
 <h4>A Estrutura de um Vírus</h4>
 
 Os vírus vêm em uma variedade de formas que são especializadas em atacar a sua célula alvo. Os dois principais componentes de todos os vírus são o genoma viral e sua camada proteica protetora, conhecida como capsídeo. O genoma viral é composto por RNA ou DNA de uma cadeia simples ou dupla, e codifica as proteínas que compõem o capsídeo. Juntos, o genoma viral e o capsídeo são conhecidos como nucleocapsídeos.
 
 Uma característica única de muitos vírus eucarióticos é a presença de uma membrana fosfolipídica, conhecida como o envelope que envolve o capsídeo. Este envelope normalmente tem origem nas membranas de células hospedeiras previamente infectadas, mas também pode incluir proteínas virais (chamadas proteínas envelope) ligadas a ele. Por fim, alguns vírus animais têm um conjunto de proteínas codificadas por vírus, o tegumento viral, no espaço entre o envelope e o capsídeo.
 
 <h4>Infeção viral</h4>
 
 O ciclo de vida viral pode ser dividido nas seguintes cinco etapas: ligação, entrada, replicação, montagem e libertação. As proteínas na superfície do vírus ajudam a reconhecer células hospedeiras específicas. Alguns vírus usam essas proteínas superficiais para ligar receptores de células hospedeiras e iniciar a internalização por endocitose, enquanto que vírus revestidos por envelope podem fundir-se diretamente com a membrana celular hospedeira.
 
 Alguns bacteriófagos não entram na célula; eles injetam o seu genoma (e enzimas virais) na célula hospedeira. Uma vez dentro da célula, o vírus é descapsulado e direciona a maquinaria da célula hospedeira a transcrever e traduzir o seu genoma. A célula hospedeira encapsula as novas cópias do genoma viral em partículas virais para produzir descendentes. Os vírus descendentes podem ser armazenados na célula hospedeira antes de serem libertados ou continuamente expelidos da célula por invaginações da membrana celular. O ciclo de infeção viral é classificado como lítico ou lisogénico. No ciclo lítico, os novos vírus explodem da célula hospedeira, matando-a no processo. No ciclo lisogénico, o DNA viral é incorporado no genoma hospedeiro onde fica dormente e é copiado de cada vez que a célula hospedeira se replica.

O que são Vírus?

Visão geral

Um vírus é uma partícula infecciosa microscópica que consiste em um genoma de RNA ou DNA encerrado em um invólucro de proteína. Não é capaz de se reproduzir em ...

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Biology

Biologia

Genetics

Genética

Viruses

Vírus

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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-LS1-1

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HS-LS1-4

How Viruses Infect Cells and Multiply

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