Retroviruses

Summary

This video explains retroviruses, a unique type of RNA virus characterized by the enzyme reverse transcriptase. The video details how retroviruses use reverse transcription to convert viral RNA into DNA, which integrates into the host cell's genome through another enzyme called integrase. Once integrated, the host cell unknowingly replicates viral RNA and proteins, creating new immature retroviruses. These new retroviruses then mature and are released to infect other cells, continuing the replication cycle. The video provides a step-by-step visual guide to this process.

Takeaways

• 🦠 Retroviruses are a type of RNA virus known for possessing the enzyme reverse transcriptase.
• 🔄 Reverse transcriptase allows the retrovirus to reverse the usual transcription process, turning viral RNA into viral DNA.
• 🧬 Retroviruses have additional enzymes like integrase, which integrate viral DNA into the host cell's DNA.
• 🧫 The retrovirus enters the host cell by fusing its lipid envelope with the host cell membrane.
• 💥 Once inside, the viral capsid breaks down, releasing viral RNA and enzymes into the host cell.
• 🔧 Reverse transcriptase binds to viral RNA, creating viral DNA, which is crucial for the virus’s replication process.
• ✂️ Integrase cuts open the host cell DNA and integrates the viral DNA into the host’s genome, forming a provirus.
• 📜 The host cell’s machinery then transcribes the viral DNA, producing multiple copies of viral RNA.
• 🛠 Ribosomes in the host cell translate viral RNA into viral proteins, including reverse transcriptase, integrase, and the viral capsid.
• 🚶‍♂️ The new viral proteins self-assemble into immature retroviruses, which are eventually released from the host cell to infect new cells.

Q & A

What is a retrovirus and what makes it unique?

A retrovirus is a specific type of RNA virus that possesses an enzyme called reverse transcriptase. This enzyme allows the virus to perform reverse transcription, converting RNA into DNA, which is the reverse of the typical transcription process.

What role does reverse transcriptase play in the life cycle of a retrovirus?

Reverse transcriptase binds to the viral RNA and performs reverse transcription, creating a DNA version of the viral RNA. This allows the retrovirus to integrate its genetic material into the host cell's DNA.

What is the function of integrase in a retrovirus?

Integrase is an enzyme that helps integrate the viral DNA into the host cell's DNA by cutting open the host's DNA and inserting the viral DNA into it.

How does the retrovirus enter a host cell?

The retrovirus attaches to the host cell membrane, and the lipid bilayers of both the virus and the cell fuse. This fusion allows the retrovirus to enter the host cell, where its capsid is dissolved to release the viral RNA and enzymes.

What is a pro-virus, and how is it formed?

A pro-virus is a combination of the host cell's DNA and the viral DNA created after the viral DNA is integrated into the host genome. This integration is facilitated by the enzyme integrase.

How does the host cell’s transcription process contribute to viral replication?

Once the viral DNA is integrated into the host DNA, the host cell's normal transcription machinery is used to create viral RNA. This viral RNA will then direct the production of viral proteins.

What happens to the viral RNA once it is created in the host cell?

The viral RNA attaches to ribosomes in the host cell, where the ribosomes read the viral RNA and produce viral proteins, such as reverse transcriptase, integrase, and the viral capsid proteins.

How are new retroviruses formed inside the host cell?

The viral proteins produced by the host cell’s ribosomes self-assemble into immature retroviruses. These immature viruses are then released through the host cell membrane.

What happens to the immature retroviruses after they are released from the host cell?

The immature retroviruses undergo a series of chemical changes to become mature. Once mature, they are capable of infecting other cells and repeating the viral replication cycle.

What are the main steps in the retrovirus replication cycle?

The main steps include: the retrovirus attaching to the host cell, reverse transcription of viral RNA into DNA, integration of viral DNA into the host cell’s genome, production of viral RNA and proteins, assembly of new viruses, and release of the newly formed viruses to infect other cells.

Outlines

00:00

🦠 Introduction to Retroviruses

In this introductory section, the speaker explains that retroviruses are a specific type of RNA virus, distinguished by their possession of the enzyme reverse transcriptase. This enzyme allows the virus to perform transcription in reverse, a process that will be explained in detail later. Additionally, retroviruses contain another key enzyme, integrase, which will play a significant role in the replication process. The structure of the retrovirus is described, highlighting the outer lipid envelope, the inner capsid, and the nucleic acid enclosed within.

05:00

🔄 Retrovirus Entry and Reverse Transcription

This part focuses on the retrovirus' initial entry into the host cell. The virus fuses with the cell membrane, allowing it to enter. The capsid of the retrovirus then dissolves, releasing enzymes and RNA into the host cell. Reverse transcription is initiated by reverse transcriptase, which uses viral RNA to create viral DNA. This process is unique to retroviruses and is crucial for their replication.

🔬 Integration of Viral DNA

The viral DNA created through reverse transcription enters the host cell's nucleus, accompanied by the integrase enzyme. Integrase's function is symbolized by scissors, as it cuts the host's DNA, allowing the viral DNA to integrate into the host genome. This combination of host DNA and viral DNA forms a 'provirus,' which will direct the host cell's machinery to produce viral components.

🧬 Viral RNA Replication

Once the viral DNA has integrated, the host cell begins to transcribe the viral DNA along with its own. Instead of producing its own RNA, the cell starts producing viral RNA. This happens repeatedly, creating multiple copies of viral RNA that will be used later to assemble new viruses.

🧪 Viral Protein Production

In this section, the viral RNA attaches to ribosomes in the host cell's cytoplasm. The ribosomes, which typically create proteins for the cell, now translate viral RNA into viral proteins, including reverse transcriptase, integrase, and capsid proteins. These proteins are crucial for assembling new retroviruses.

🧩 Assembly and Release of New Viruses

The viral proteins created by the ribosomes self-assemble into immature retroviruses. These newly formed viruses bud out of the host cell membrane and are released. Though initially immature, they undergo chemical changes to become mature retroviruses capable of infecting other cells and repeating the replication cycle.

🔁 Summary of Retrovirus Replication

The final part of the video recaps the retrovirus replication process. The retrovirus enters the host cell, reverse transcription occurs to produce viral DNA, which integrates into the host's DNA. The host cell then produces viral RNA and proteins, which self-assemble into new viruses. These newly formed retroviruses are released, allowing the cycle to repeat. Viewers are thanked for watching and encouraged to share their thoughts in the comments.

Keywords

💡Retrovirus

A retrovirus is a type of RNA virus that is unique because it has an enzyme called reverse transcriptase, allowing it to convert its RNA into DNA once inside a host cell. In the video, retroviruses are central to the discussion as they replicate by integrating their viral DNA into the host cell's genome, making them a key subject of study.

💡Reverse Transcriptase

Reverse transcriptase is an enzyme used by retroviruses to convert their RNA into DNA, a process that reverses normal transcription. The video highlights this enzyme as a key player in retrovirus replication, where it builds viral DNA from viral RNA, allowing the virus to infiltrate the host cell's genome.

💡Transcription

Transcription is the biological process in which a DNA sequence is copied into RNA. In the video, this term is important because reverse transcriptase enables retroviruses to perform transcription in reverse, converting RNA back into DNA, which is unusual compared to most viruses.

💡Integrase

Integrase is another important enzyme in retroviruses, responsible for cutting the host's DNA and inserting the viral DNA into it. This is crucial for the integration of the viral genome into the host cell's genome, a key step in the replication of retroviruses explained in the video.

💡Capsid

The capsid is the protein shell of a virus that encases the viral RNA and enzymes. In the video, it is described as breaking down once the retrovirus enters the host cell, releasing the viral RNA and enzymes such as reverse transcriptase and integrase to begin replication.

💡Provirus

A provirus is the integrated form of viral DNA within a host cell's genome. Once integrase has inserted the viral DNA into the host’s DNA, the combination is called a provirus. The video explains how this allows the host cell to replicate the virus each time it replicates its own DNA.

💡Ribosome

Ribosomes are cellular structures that translate RNA into proteins. In the video, the retrovirus exploits the host cell's ribosomes to create viral proteins, including components like reverse transcriptase and integrase, enabling the formation of new viruses.

💡Translation

Translation is the process by which ribosomes convert RNA into proteins. In the video, this process is manipulated by the retrovirus, where viral RNA is translated by the host's ribosomes into viral proteins, such as the capsid and enzymes necessary for creating new viruses.

💡Lipid Bilayer

The lipid bilayer is the double-layered membrane surrounding the retrovirus, composed of lipids. In the video, it is noted that this bilayer fuses with the host cell's membrane, allowing the virus to enter the host cell and begin the replication process.

💡Replication

Replication refers to the process by which viruses reproduce and create copies of themselves. In the video, the retrovirus replication cycle is outlined, showing how it enters a host cell, integrates its DNA into the host genome, and hijacks the host's cellular machinery to create new viral particles.

Highlights

Retroviruses are a specific type of RNA virus that possess an enzyme called reverse transcriptase.

Reverse transcriptase allows retroviruses to perform reverse transcription, creating viral DNA from viral RNA.

The viral DNA created through reverse transcription is integrated into the host cell's DNA by an enzyme called integrase.

Integrase is responsible for cutting open the host DNA and integrating the viral DNA, forming a pro-virus.

The host cell's normal transcription process is hijacked, producing viral RNA instead of cellular RNA.

Viral RNA is used by the host cell's ribosomes to create viral proteins, such as reverse transcriptase and integrase.

The viral proteins produced in the cell self-assemble into immature retroviruses.

These immature viruses bud off from the host cell membrane and are released to infect new cells.

Over time, immature viruses undergo chemical changes to become mature retroviruses capable of repeating the cycle.

The retrovirus replication cycle begins when the virus attaches and enters the host cell, releasing its enzymes and RNA.

Once inside the host cell, the capsid of the retrovirus dissolves, releasing the viral enzymes and RNA.

During reverse transcription, viral RNA is used to build a molecule of viral DNA, reversing the usual flow of genetic information.

Viral RNA is repeatedly created during the normal transcription process, leading to multiple copies of viral RNA.

The process of translation allows the viral RNA to be read by the ribosome, resulting in the production of viral proteins.

Newly formed retroviruses are released from the host cell membrane, marking the completion of the replication cycle.

Transcripts

okay so in this video we're going to

discuss retroviruses so let's go ahead

and get started you know as far as

viruses go there are several different

categories and types of viruses but

retroviruses are a specific type of RNA

virus and what makes them so unique is

that they possess an enzyme by the name

of reverse transcriptase typically if

you if you look at molecules and if a

molecule ends with the letters ASE it's

some kind of enzyme and that's what

reverse transcriptase is now in the

named reverse transcriptase you know

reverse means to go backwards and when

you hear the word transcriptase perhaps

you think of the process of

transcription so when we get into this

video in a little bit what you're going

to see is the process of transcription

going backwards that'll be more clear

when we get further into the video so in

my picture here there is this red circle

labeled reverse transcriptase and

there's other enzymes in the retrovirus

as well one very important enzyme is a

enzyme called integrase and you'll

understand why it's called integrase

later notice how there's also an outer

envelope that surrounds the entire

retrovirus and also an inner capsid that

surrounds the nucleic acid and the

enzymes but what we're going to do is

we're going to look at the steps that a

retrovirus goes through in order to

replicate so you have the key in the

upper left hand corner so you know what

everything is in my animation so what

how this process begins is the

retrovirus will attach and then enter

into the host cell so here comes our

retrovirus and it's just attached to the

cell membrane of the host the outer

envelope of the retrovirus is a lipid by

a phospholipid bilayer so the to fuse

together and as they fuse together the

retrovirus is taken into the host cell

well now which have not watch

what happens to the yellow capsid the

yellow capsid is dissolved and begins to

break down

this releases the enzymes of the

retrovirus and the RNA nucleic acid of

the retrovirus so the next step is going

to be the process of reverse

transcription now normally when I hear

the word transcription I think of this a

DNA molecule is used to create an RNA

molecule

however retroviruses because they have

that enzyme called reverse transcriptase

are able to perform transcription in

reverse reverse transcriptase will

actually bind to the virus RNA and

perform reverse transcription the viral

RNA will be used to build a molecule of

viral DNA and eventually the enzyme

reverse transcriptase is degraded and

broken down but more importantly the

retrovirus has created viral DNA for

itself and you're going to see why

that's important right now so as we move

on to the next step the DNA of the virus

that was just created will actually

enter into the nucleus along with the

enzyme called integrates now there's a

reason I've drawn integrase to kind of

look like a pair of scissors here to be

symbolic of what it performs integrase

will actually cut open the DNA of the

host cell and it's called integrase

because it helps to integrate the DNA of

the virus into the DNA of the host cell

that's why it's called integrase and

what this creates is this combination of

host cell DNA and viral DNA that is

known as a pro virus and so now when we

look at the next step viral RNA will be

created each time the host cell

transcribes its DNA so inside the host

cell our enzyme

that will direct the normal process of

transcription which is a using DNA to

make a molecule of RNA so in the nucleus

here is an enzyme that the cell

possesses and it will do normal

transcription notice what it did though

it made a copy of not cell RNA it made a

copy of viral RNA and so this happens

many many times and here we have another

copy of viral RNA being created and I

think I have five of them in my

animation so there's a third one and

here's a fourth copy of viral RNA being

made and lastly a fifth copy of viral

RNA being made through the normal

transcription process and so now what

happens is we're going to see the

purpose of making all this viral RNA

keep in mind in the cytoplasm of a cell

cells possess ribosomes now they possess

many ribosomes I'm just showing one here

for simplicity so what happens is the

viral RNA attaches to a ribosome and

through the process of translation the

ribosome will read the viral RNA and

create viral proteins viral proteins

such as reverse transcriptase as the

process of as this process continues the

ribosome will continue to read other

viral RNAs and create integrase the

viral protein called integrase and so if

you see what's happening the cells own

ribosomes are creating parts for new

viruses and as this process continues

the ribosome also creates the capsid of

a virus the capsid of a virus is simply

made from protein and that's what the

ribosome builds the ribosome builds

proteins it just so happens that the

proteins belong to viruses instead of

important parts needed by our cells to

survive

and so eventually these viral proteins

that the cells own ribosome created will

self assemble into immature viruses so

here we have the viral proteins self

assembling into retroviruses into new

immature retroviruses and eventually

these these immature viruses are

released through the cell membrane so

notice how the cell membrane has began

to bud out and as the process continues

the cell membrane continues to butt out

and bulge out until eventually there you

go a retrovirus has been released now

the same thing will happen with the

other two retroviruses in the cell but

this is how new viruses are created that

will then be released to repeat the

cycle eventually these immature viruses

will go through a series of of chemical

changes to become mature but then

they'll be able to repeat the cycle and

infect other cells if we finish this

video with a quick summary of what we've

learned here's a retrovirus entering its

genetic material into a host cell and

then the the process of reverse

transcription is performed to make DNA

of the of the retrovirus that viral DNA

is then integrated into the the host

cell's DNA into the genome of the host

cell this process will then direct the

duplication in the creation of a whole

bunch of viral RNA and viral proteins

the viral RNA and proteins will self

assemble into new retroviruses that will

be released so this is the cycle of how

a retrovirus replicates I hope you found

this video helpful and thank you for

watching and place your comments in the

box below I'd like to hear what you

think