This lesson will give you a basic overview of how DNA viruses replicate inside of a host cell. We will cover the entry, integration, replication and release of DNA viruses.
DNA Replications Strategies
Some of the most well-known viruses, such as those that cause herpes, smallpox, hepatitis and warts, have a DNA based genome.
These viruses must have slightly different replication schemes compared to their RNA brethren in order to make a living. That’s because their genome is the same type of genome as their host animal cell. However, the problem is that certain DNA viruses don’t follow the same replication schemes as most other DNA viruses. There are exceptions to everything in science, and in order to avoid giving you a massive headache, we’ll focus in on the core basics of the replication sites, schemes and terms associated with DNA viruses.
Entry and Integration of DNA Viruses
DNA viruses that infect humans have a double-stranded DNA genome encased in a protective shell, called a capsid, which may in turn be enclosed in an envelope. These envelopes give viruses certain advantages, like ease of infection. On the flipside, an envelope makes a virus more sensitive to environmental destruction.
In any case, once the virus gains entry into the human body, it must touchdown on the surface of a cell it’s going to infect. I picture it almost like a moon landing of sorts. Viruses have little adhesion molecules, like legs on a lunar module, that will stick to the surface of a cell, or the moon’s crust. Once the virus, our lunar module, touches down on the surface of its cell, it will then trick the cell into allowing it entry into the cytoplasm, or the mantle of the moon. After drilling down below the surface of the moon, through the mantle, or cytoplasm, the DNA viral genome enters into the core of the moon, or the nucleus of the cell. This is where it will do its dirty work.
Replication and Release of DNA Viruses
Once the viral DNA is integrated into the host DNA, this provirus uses the host cell machinery to copy its genome for future virus babies.
In addition, it uses the host cell’s polymerase, an enzyme that catalyzes the formation of nucleic acids, to make mRNA from its DNA in a process known as transcription. After the mRNA is made, it is sent to the host cell’s ribosomes, which are the protein builders of the cell. You can think of the mRNA as one of those barcodes on the receipt of a product you may have recently bought. The ribosome will scan the barcode and will produce a product. Each barcode from each virus may be a bit different. Hence, when the ribosome, like a clerk at a store, scans the barcode, they will go get you a different type of product.
In this case, these products are proteins and enzymes that are used to either build the structural components of the virus, such as the capsid, or adhesion molecules, I mentioned before. Or, in some cases, they are enzymes that will be utilized for replication. In addition to making proteins and enzymes, the viral DNA must also be copied. Once this has been done, the DNA, along with the proteins for the structural components, are all packaged up into a neat little viral bundle. This bundle will need to leave the moon and may do so through different mechanisms, such as budding or lysis.
The basic cycle we went over is just that, the basics of what actually occurs. There are exceptions to every rule. While as a general rule DNA viruses replicate in the nucleus, as opposed to the cytoplasm, the smallpox virus is a notable exception. Smallpox is also an exception because it contains its own prepackaged, virally-coded replication enzymes, unlike many other DNA viruses, which is what allows it to replicate in the cytoplasm in the first place.
With that in mind, let’s review the key terms we discussed in this lesson.
DNA viruses use the host cell’s polymerase, an enzyme that catalyzes the formation of nucleic acids to make mRNA from its DNA in a process known as transcription, which is a process whereby DNA is converted into mRNA. After transcription occurs, the mRNA is taken to a few clerks at a store. These clerks, called ribosomes, scan the mRNA barcode in order to produce a product, or viral protein. So, the ribosomes are basically the protein builders of the cell. The viral DNA is also replicated. The proteins made by the host cell’s ribosomes combine with the replicated viral genome to form a baby virus, which shoots off the moon in order to land on the surface of another moon far, far away.
After viewing this video lesson, you should be able to describe the replication of DNA viruses using transcription.