Retroviruses: Unique Characteristics

Questions and Answers

What type of virus is a retrovirus?

Enveloped DNA virus

Non-enveloped RNA virus

Double-stranded DNA virus

Single-stranded RNA virus (correct)

How does the retrovirus HIV enter the cell?

Through lytic replication

Through lysogenic replication

Through direct fusion (correct)

Through receptor-mediated endocytosis

What is the function of the protein reverse transcriptase?

To replicate DNA

To reverse transcribe RNA into DNA (correct)

To transcribe DNA into RNA

To translate RNA into protein

What is the product of reverse transcription?

Complementary DNA Signup and view all the answers

What is the direction of reading during reverse transcription?

From 5' to 3' prime end Signup and view all the answers

What is the purpose of the uncoating step in retroviral replication?

To release the viral genome from the capsid Signup and view all the answers

How many special proteins are carried by the retrovirus inside its envelope?

Three Signup and view all the answers

What is the name of the final product of reverse transcription?

cDNA Signup and view all the answers

What is the purpose of integrase in the HIV replication cycle?

To clip off the 3' ends of cDNA strands to form sticky ends Signup and view all the answers

What happens to the RNA strand after integrase clips off the 3' ends?

It gets degraded by normal ribonuclease Signup and view all the answers

What is the term for the integrated viral DNA in the host genome?

Provirus stage Signup and view all the answers

What is the function of the protease in the HIV replication cycle?

To cleave the viral proteins to make them fully functional Signup and view all the answers

What is unique about the provirus stage compared to the regular lysogenic cycle?

It does not have a repressor gene Signup and view all the answers

What happens to the viral mRNA after it exits the nucleus?

It gets translated into proteins Signup and view all the answers

What is the term for the viruses that have not yet matured and are still missing their envelope?

Immature viruses Signup and view all the answers

What happens to the immature viruses before they infect other cells?

They bud off from the host cell's membrane Signup and view all the answers

What is the purpose of the retrovirus replication cycle?

To produce new viruses that can infect other cells Signup and view all the answers

What is unique about the HIV replication cycle compared to traditional replication?

It has elements of both lysogenic and lytic cycles Signup and view all the answers

Study Notes

Retroviruses

Retroviruses are a special case of viruses that don't fit into the lytic or lysogenic categories.
They are enveloped, single-stranded RNA viruses that carry three special proteins.

Entry into the Cell

Retroviruses enter the cell through direct fusion.
After entry, the nucleocapsid undergoes uncoating, releasing the proteins and RNA.

Reverse Transcription

The red protein, reverse transcriptase, reads the RNA from 5' to 3' end and forms complementary DNA (cDNA).
Reverse transcriptase works again on the RNA to make another cDNA strand, which recombines with the first cDNA strand to form a double-stranded DNA.

Integration

The blue protein, integrase, clips off the 3' ends of the DNA strands, forming sticky ends.
Integrase integrates the viral DNA into the host's DNA.
The viral DNA is now part of the host's genome, known as the provirus stage.

Transcription and Translation

The host cell transcribes the viral DNA into viral mRNA, which exits the nucleus.
The viral mRNA is translated into proteins, including the capsid proteins, reverse transcriptase, integrase, and protease.

Assembly and Budding

The newly formed proteins and RNA self-assemble into new viruses, minus the envelope.
These immature viruses bud off from the host cell, taking a piece of the membrane with them.
The resulting viruses are still immature and require maturation.

Maturation

The green protein, protease, cleaves the proteins to make them fully functional.
This maturation process occurs before the virus infects another cell and starts the replication cycle again.

Retrovirus Replication

Retrovirus replication is a unique process that combines elements of both lysogenic and lytic cycles.
It involves reverse transcription, integration, transcription, translation, assembly, budding, and maturation.