VIRUS HELP

[pizza1994]

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Hey guys,

so why is it that animal viruses have an envelope but plant viruses and bacteriophages do not? I cant visualize this.

Any help would be greatly appreciated!

Thanks 🙂

 

[SuperSneaky24]

So the envelope is formed by the virus budding out of the cell membrane like a vesicle, thereby containing all the membrane proteins and glycoproteins of its host, which helps attachment to its future hosts. Now my guess is that plants have cell walls and therefore block the virus from budding off due to rigid cellulose blocking the plasma membrane.

I'm not exactly sure why bacteriophages don't envelope off though? I can totally see them budding off. A little googling showed me only a few bacteriophages are enveloped. My guess is that bacteria are too simple, so any membrane proteins and glycoproteins they have doesn't help the virus in future attachment.

 

[Lunasly]

Animal cells do not have cell walls. Therefore, when newly made animal viruses are produced in the animal cell, they excise themselves from the cell without lysing the cell in the process (as would occur had they undergone the lytic cycle). The lytic cycle is not beneficial for the virus. It would much rather keep the host cell alive such that its progeny can continue to use it to produce more viruses. To do this, they need an envelope (an envelope contains all of the components that a plasma membrane would have). This allows a virus that already have a coat to enter an animal host cell via endocytosis or newly made viruses to leave the host cell via exocytosis, without lysing the cell.

Bacteriophages and plant viruses don't have or develop envelopes because bacteria and plants have cell walls (a distinguishing characteristic between them and animal cells; e.g., think gram-negative and gram-positive bacteria). An envelope would be of no use in this regard. The cell wall of a bacteria is made of a peptidoglycan polymer. Having a lipid based envelope will not help the virus leave the cell via exocytosis.

Therefore, bacteriophages and plant viruses have to infect their host by penetrating the cell and releasing their genome along with any other components required for its replication in order to reproduce.

TL;DR: An envelope would not be of any use to them given that plants and bacteria have cell walls, while animal cells do not.

 

[SuperSneaky24]

Animal cells do not have cell walls. Therefore, when newly made animal viruses are produced in the animal cell, they do so without lysing the cell in the process (as would occur has they undergone the lytic cycle). The lytic cycle is not beneficial for the virus. It would much rather keep the host cell alive such that its progeny can continue to use it to produce more viruses. To do this, they need an envelope (an envelope contains all of the components that a plasma membrane would have). This allows a virus that already have a coat to enter an animal host cell via endocytosis or newly made viruses to leave the host cell via exocytosis, without lysing the cell.

Bacteriophages and plant viruses don't have or develop envelopes because bacteria and plants have cell walls (a distinguishing characteristic between them and animal cells; e.g., think gram-negative and gram-positive bacteria). An envelope would be of no use in this regard. The cell wall of a bacteria is made of a peptidoglycan polymer. Having a lipid based envelope will not help the virus leave the cell via exocytosis.

Therefore, bacteriophages and plant viruses have to infect their host by penetrating the cell and releasing their genome along with any other components required for its replication in order to reproduce.

TL;DR: An envelope would not be of any use to them given that plants and bacteria have cell walls, while animal cells do not.

Lol I totally forgot that bacteria have cell walls as well. I'm so stupid 😛

 

[pizza1994]

Animal cells do not have cell walls. Therefore, when newly made animal viruses are produced in the animal cell, they excise themselves from the cell without lysing the cell in the process (as would occur had they undergone the lytic cycle). The lytic cycle is not beneficial for the virus. It would much rather keep the host cell alive such that its progeny can continue to use it to produce more viruses. To do this, they need an envelope (an envelope contains all of the components that a plasma membrane would have). This allows a virus that already have a coat to enter an animal host cell via endocytosis or newly made viruses to leave the host cell via exocytosis, without lysing the cell.

Bacteriophages and plant viruses don't have or develop envelopes because bacteria and plants have cell walls (a distinguishing characteristic between them and animal cells; e.g., think gram-negative and gram-positive bacteria). An envelope would be of no use in this regard. The cell wall of a bacteria is made of a peptidoglycan polymer. Having a lipid based envelope will not help the virus leave the cell via exocytosis.

Therefore, bacteriophages and plant viruses have to infect their host by penetrating the cell and releasing their genome along with any other components required for its replication in order to reproduce.

TL;DR: An envelope would not be of any use to them given that plants and bacteria have cell walls, while animal cells do not.

So when you say that bacteria and plant cells have cell walls and that an envelope would be of no use.....I dont get that. Like why not?

 

[SuperSneaky24]

Well bacteria and plant cells have cell walls, so an envelope wouldn't be formed in the first place. A virus has an envelope because it contains glycoproteins or other membrane proteins that its host has to facilitate attachment to a future host or bypass any immune system response. With bacteria and plants, their cell wall not only prevents the envelope from being formed, but if somehow an envelope is formed in the virus, the cell wall blocks the envelope from interacting with the plasma membrane.

 

[pizza1994]

ALSO, do any of you know why is it that a virus that enters the lysogenic cycle will eventaully after enter the lytic cycle? I mean the point of the lysogenic cycle if to keep the host alive....and so why would they enter the lytic cycle after being excised from the prophage?

 

[pizza1994]

Well bacteria and plant cells have cell walls, so an envelope wouldn't be formed in the first place. A virus has an envelope because it contains glycoproteins or other membrane proteins that its host has to facilitate attachment to a future host or bypass any immune system response. With bacteria and plants, their cell wall not only prevents the envelope from being formed, but if somehow an envelope is formed in the virus, the cell wall blocks the envelope from interacting with the plasma membrane.

ahhh makes sense!! Thanks guys 🙂

 

[SuperSneaky24]

ALSO, do any of you know why is it that a virus that enters the lysogenic cycle will eventaully after enter the lytic cycle? I mean the point of the lysogenic cycle if to keep the host alive....and so why would they enter the lytic cycle after being excised from the prophage?

Aha well if the virus stays the lysogenic cycle its whole life, then how in the world will it ever replicate and create more of itself?

 

[pizza1994]

but the lysogenic cycle does replicate the prophage doesnt it? So isnt that the same thing?

 

[SuperSneaky24]

Well yes but remember that only the genome of the virus is replicated in this case. The virus' genetic material is simply integrated and replicated into its host cells, and that's it. The lytic cycle is when the virus' genetic material actually takes a hold of the host's machinery to create a ton of viruses. So in order for a lysogenic cycle to be effective, it absolutely HAS to transition to the lytic cycle. Otherwise, the virus' genome would simply remain in the host's genome, and nothing would happe.

 

[Lunasly]

No, the lysogenic cycle just means that the viral genome incorporates itself into the bacterial genome. I'm not sure of the reasoning, but I believe it might be a safety mechanism. Perhaps conditions for replication aren't optimal. When the viral genome becomes activated, it begins the replication and translation process and then excises itself from the bacterium.

 

[pizza1994]

Well yes but remember that only the genome of the virus is replicated in this case. The virus' genetic material is simply integrated and replicated into its host cells, and that's it. The lytic cycle is when the virus' genetic material actually takes a hold of the host's machinery to create a ton of viruses. So in order for a lysogenic cycle to be effective, it absolutely HAS to transition to the lytic cycle. Otherwise, the virus' genome would simply remain in the host's genome, and nothing would happe.

Okay so then what is the point of the lysogenic cycle at all? I mean if eventually it has to undergo the lytic cycle to make more viruses then why would something wanna go through the lysogenic cycle? Before I thought that the lysogenic cycle keeps making more viruses which are integrated in the host genome and then UV radiation will activate the virus. But I thought this was all part of the lysogenic cycle?

 

[tdod]

by entering the lysogenic cycle, the bacteria can wait for optimal conditions before entering the lytic cycle. thus, it ensures that it has the greatest likelihood of replicating when it destroys its host.

 

[pizza1994]

alright i get this now! thanks guys 🙂