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?

- [Instructeur] Een virus is een structuur die zijn eigen genomisch materiaal draagt in de vorm van RNA of DNA om een gastcel binnen te dringen en te vermenigvuldigen. Nadat een virus zich aan de oppervlakte-receptoren op de gastheercel bindt, komt het virus binnen en wordt het snel gedemonteerd, zijn genetisch materiaal decoderend. In het geval van DNA-virussen stuurt het virale DNA de replicatieproteïnen van de gastcellen aan om nieuwe kopieën van het virale genoom te synthetiseren, die vervolgens worden getranscribeerd en vertaald in virale eiwitten.

Ten slotte brengt de gastheer deze virale componenten weer samen tot nageslacht, waardoor één enkel virusdeeltje nog duizenden meer kan produceren, wat vaak leidt tot de dood van de gastheercel.

wat zijn virussen?

Overzicht

Een virus is een microscopisch klein infectieus deeltje dat bestaat uit een RNA- of DNA-genoom ingesloten in een eiwitomhulsel. Het kan zich niet zelfstandig voortplanten: het kan alleen meer virussen maken door een cel binnen te gaan en zijn cellulaire machinerie te gebruiken. Wanneer een virus een gastheercel infecteert, verwijdert het zijn eiwitmantel en stuurt het de machinerie van de gastheer aan om zijn genetisch materiaal te transcriberen en te vertalen. De gekaapte cel voegt de gerepliceerde componenten samen tot duizenden virale nakomelingen, die de gastheercel kunnen scheuren en doden. De nieuwe virussen infecteren vervolgens meer gastheercellen.

Waarom virussen bestuderen?

Virussen kunnen verschillende soorten cellen infecteren: bacteriën, planten en dieren. Virussen die zich op bacteriën richten, bacteriofagen (of fagen) genoemd, zijn zeer overvloedig aanwezig. Huidig onderzoek richt zich op faagtherapie om multiresistente bacteriële infecties bij mensen te behandelen. Virussen die gecultiveerde planten infecteren, worden ook uitgebreid bestudeerd, omdat epidemieën tot enorme oogst- en economische verliezen leiden.

Virussen werden voor het eerst ontdekt in de 19e eeuw toen een economisch belangrijk gewas, de tabaksplant, werd geplaagd door een mysterieuze ziekte - later geïdentificeerd als het tabaksmozaïekvirus. Dierlijke virussen zijn van groot belang, zowel in het veterinaire onderzoek als in het medisch onderzoek. Bovendien liggen virussen ten grondslag aan veel ziekten bij de mens, variërend van verkoudheid, waterpokken en herpes tot gevaarlijkere infecties zoals gele koorts, hepatitis en pokken.

De structuur van een virus

Virussen zijn er in verschillende vormen die gespecialiseerd zijn in het aanvallen van hun doelcel. De twee belangrijkste componenten van alle virussen zijn het virale genoom en de beschermende eiwitlaag ervan, bekend als de capside. Het virale genoom bestaat uit enkel- of dubbelstrengs RNA of DNA en codeert voor de eiwitten waaruit het capside bestaat. Samen staan het virale genoom en het capside bekend als het nucleocapside.

Een uniek kenmerk van veel eukaryote virussen is de aanwezigheid van een fosfolipidemembraan, bekend als de envelop die de capside omringt. Deze envelop is doorgaans afkomstig van de membranen van eerder geïnfecteerde gastheercellen, maar kan ook virale eiwitten bevatten (envelopeiwitten genoemd) die eraan vastzitten. Ten slotte hebben sommige dierlijke virussen een cluster van virusgecodeerde eiwitten, het virale tegument, in de ruimte bevinden de envelop en het capside.

Virale infectie

De virale levenscyclus kan worden opgedeeld in de volgende vijf stappen: aanadhesie, binnenkomst, replicatie, assemblage en vrijgave. De eiwitten op het oppervlak van het virus helpen het specifieke gastheercellen te herkennen. Sommige virussen gebruiken deze oppervlakte-eiwitten om gastheercelreceptoren te binden en internalisatie door endocytose te initiëren, terwijl omhullende virussen direct kunnen fuseren met het gastheercelmembraan.

Sommige bacteriofagen komen de cel niet binnen; ze injecteren hun genoom (en virale enzymen) in de gastheercel. Eenmaal in de cel wordt het virus ongecoat en stuurt het de machinerie van de gastheercel aan om zijn genoom te transcriberen en te vertalen. De gastheercel verpakt de nieuwe kopieën van het virale genoom in virale deeltjes om nageslacht te maken. De nageslachtvirussen kunnen vóór vrijgave in de gastheercel worden opgeslagen of voortdurend uit de cel worden geëxtrudeerd door uit het celmembraan te ontkiemen. De virale infectiecyclus wordt geclassificeerd als lytisch of lysogeen. In de lytische cyclus barsten de nieuwe virussen uit de gastheercel, waardoor deze wordt gedood. In de lysogene cyclus wordt het virale DNA in het gastheergenoom opgenomen, waar het inactief blijft en elke keer dat de gastheercel repliceert, wordt gekopieerd.

Wat zijn virussen?

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.

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How Viruses Infect Cells and Multiply

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