Animal Viruses: Reverse-Transcribing Virus Synthesis & Replication - Online Tutor, Practice Problems & Exam Prep

Reverse transcribing viruses, particularly retroviruses, utilize the enzyme reverse transcriptase to convert their single-stranded RNA genome into double-stranded DNA. This process begins when the virus injects its RNA and reverse transcriptase into a host cell, leading to the synthesis of complementary DNA strands. The resulting double-stranded DNA can integrate into the host's chromosome, allowing for latent infections and replication alongside the host cell. This mechanism is crucial for understanding viral replication and pathogenesis, particularly in diseases caused by retroviruses like HIV.

Animal Viruses: Reverse-Transcribing Virus Synthesis & Replication

In this video, we're going to continue to talk about animal viruses and animal virus infections by specifically focusing on reverse transcribing virus synthesis and replication. And so reverse transcribing viruses are specific types of RNA viruses that encode the enzyme called reverse transcriptase. And so reverse transcriptase is an enzyme that serves as an RNA dependent DNA polymerase, which means that this is an enzyme that uses RNA as a template to make DNA. And, really, this is the reverse of transcription, which is really where it gets its name from, reverse transcriptase as the reverse of transcription. And so, here in this video, we're mainly going to be focusing on retroviruses. And so retroviruses are specific types of reverse transcribing viruses that have a plus ssRNA genome or a plus single stranded RNA genome. And of course, because they are reverse transcribing viruses, they will also have the enzyme reverse transcriptase. And so after entry into the cell, the retrovirus is going to inject both the plus ssRNA genome as well as the reverse transcriptase. And so the reverse transcriptase enzyme is able to use the plus ssRNA genome as a template in order to make minus ssDNA.

And so if we take a look at our image down below over here on the left hand side, we're showing you that upon entry into the host cell, the retrovirus will inject its genome, which is a plus ssRNA genome. And it will also inject the enzyme reverse transcriptase. And so reverse transcriptase, the enzyme, is able to use the plus ssRNA as a template to build a minus ssDNA. And so it is using the RNA to build DNA. Then the minus ssDNA is going to be used to build a complementary DNA strand to form the plus-minus double stranded DNA or dsDNA. And so notice down below that the minus ssDNA, the single stranded DNA, is going to be used to build the complementary strand so that it is now a plus-minus double stranded DNA molecule. And from here, the plus-minus double stranded DNA molecule can be transcribed to form more plus ssRNA, which recall is a messenger RNA, and that messenger RNA can be translated to form viral proteins, and or it could be used to replicate the original plus ssRNA genome. And so remember that the original genome of the virus that is injected is always going to be regenerated, over, at the end of genome replication. So we have another plus ssRNA over here.

And so another important feature to keep in mind is that this plus-minus double stranded DNA molecule that's right here, it can also have the ability to integrate itself into the host cell's chromosome in order to become latent or dormant or silent inside of the host cell. And, again, it can replicate along with the host cell as the host cell replicates. And so this here concludes our brief introduction to reverse transcribing viruses and how they synthesize proteins and replicate their genomes. And so we'll be able to get some practice applying these concepts as we move forward in our course, And so I'll see you all in our next video.

Which of the following characteristics correctly describes retroviruses?

• A. They are made up of only a single protein.
• B. They can only reproduce by infecting bacteria.
• C. They have single-stranded DNA that acts as a template for DNA synthesis.
• D. They have single-stranded RNA that acts as a template for DNA synthesis.

A retrovirus _____.

• A. Is a DNA virus.
• B. Integrates viral DNA into the host chromosome.
• C. Requires the viral protein replicase to replicate its genome.
• D. All of the above.

The human immunodeficiency virus (HIV) is a retrovirus. HIV will not be able to integrate its viral genome into the host cell's genome unless it carries which enzyme in its viral particle?

• A. Replicase.
• B. Reverse transcriptase.
• C. DNA polymerase.
• D. Transcriptase.

Here’s what students ask on this topic:

What is the role of reverse transcriptase in retroviruses?

Reverse transcriptase is an enzyme crucial for retroviruses, such as HIV. It functions as an RNA-dependent DNA polymerase, meaning it uses the viral RNA genome as a template to synthesize complementary DNA (cDNA). This process is the reverse of normal transcription, hence the name 'reverse transcriptase.' After the retrovirus injects its RNA and reverse transcriptase into a host cell, the enzyme converts the single-stranded RNA (ssRNA) into single-stranded DNA (ssDNA). This ssDNA is then used to create a double-stranded DNA (dsDNA) molecule, which can integrate into the host cell's genome, allowing the virus to replicate and persist within the host.

How do retroviruses integrate their DNA into the host genome?

Retroviruses integrate their DNA into the host genome through a multi-step process. After the retrovirus injects its RNA and reverse transcriptase into the host cell, the reverse transcriptase converts the viral RNA into double-stranded DNA (dsDNA). This dsDNA is then transported into the host cell's nucleus. An enzyme called integrase, also encoded by the retrovirus, facilitates the integration of the viral dsDNA into the host cell's chromosomal DNA. Once integrated, the viral DNA can be transcribed and translated by the host cell's machinery, leading to the production of new viral particles and potentially causing latent infections.

What is the significance of the plus single-stranded RNA (ssRNA) genome in retroviruses?

The plus single-stranded RNA (ssRNA) genome in retroviruses is significant because it serves as the initial template for reverse transcription. Upon entry into the host cell, the retrovirus injects this plus ssRNA along with the enzyme reverse transcriptase. The reverse transcriptase uses the plus ssRNA to synthesize a complementary minus single-stranded DNA (ssDNA). This minus ssDNA is then used to create a double-stranded DNA (dsDNA) molecule. The plus ssRNA genome is crucial for the initial steps of viral replication and for the eventual production of new viral RNA genomes and proteins.

How does the integration of viral DNA into the host genome contribute to viral latency?

The integration of viral DNA into the host genome is a key factor in viral latency. Once the double-stranded DNA (dsDNA) of the retrovirus integrates into the host cell's chromosomal DNA, it can remain dormant or silent for extended periods. During this latent phase, the viral DNA is replicated along with the host cell's DNA during cell division, but it does not produce new viral particles. This allows the virus to evade the host's immune system and persist in the host. When conditions become favorable, the integrated viral DNA can be reactivated, leading to the production of new viral particles and potentially causing disease symptoms.

What are the steps involved in the replication cycle of retroviruses?

The replication cycle of retroviruses involves several key steps: 1) Entry: The retrovirus binds to and enters the host cell. 2) Reverse Transcription: The viral RNA genome and reverse transcriptase are released into the host cell. Reverse transcriptase converts the viral RNA into double-stranded DNA (dsDNA). 3) Integration: The dsDNA is transported into the nucleus and integrated into the host cell's genome by the enzyme integrase. 4) Transcription and Translation: The integrated viral DNA is transcribed into viral RNA by the host's machinery. This RNA serves as both mRNA for protein synthesis and as new viral genomes. 5) Assembly: New viral particles are assembled from the synthesized proteins and RNA genomes. 6) Release: The new viral particles are released from the host cell to infect other cells.