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Replication of RNA Viruses

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  • 0:05 RNA Replications Strategies
  • 0:34 Double Stranded,…
  • 3:35 Reverse Transcription
  • 5:02 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will give you a basic overview of how different types of RNA viruses replicate inside of an animal cell. We will cover the essence of being double-stranded and retroviruses, as well as positive-and negative-sense RNA viruses.

RNA Replications Strategies

The exact nature of how viruses, RNA or DNA, replicate inside of a cell is not fully understood. This problem is compounded by the fact that there are many different types of viruses, and all have slightly unique replication strategies. Hence, in order to avoid massive headaches and delving into things way beyond the scope of this course, we will cover just the basics of the viral replication strategies different types of RNA viruses use.

Double-Stranded, Positive and Negative Sense

In another lesson, we discussed the fact that single-stranded RNA viruses can have a positive or negative sense to their genome. This little tidbit is critical when it comes to understanding their viral replication strategies.

I like to think of positive-sense single-stranded RNA viruses as an Alka-Seltzer tablet and the cytoplasm of the cell as the water in the cup or host cell. I know it sounds weird, but that way you'll remember it better. When the tablet is dropped into the water, or the +ssRNA virus penetrates into the cell's cytoplasm, all sorts of little round bubbles start being produced instantaneously! Those little bubbles in the water are the proteins being produced by the host cell's machinery.

What happens is that the +ssRNA strand is of the same sense as mRNA, and mRNA is a molecule that is used by ribosomes during the process of translation in order to create proteins. Hence, +ssRNA can be immediately used by the cell's ribosomes to produce the little bubbles, or proteins. These proteins will then help make up the things the virus needs, from the protein capsid that houses its genome to the viral proteins that help it attach to and infect another cell to the enzymes it needs to copy its genome.

This replication scheme is slightly different from -ssRNA viruses. These viruses must have an RNA-dependent RNA polymerase, RdRp, before it enters the cell. This is an enzyme that converts one strand of RNA to a strand of RNA that has a complementary sense. So when the negative-sense RNA genome enters the host cell's cytoplasm, it uses its own RdRp to copy its negative-sense RNA into positive-sense RNA, which can then be used like the Alka-Seltzer tablet to produce not only structural proteins and enzymes for genome replication but also for additional copies of RdRp that will need to be packaged into the baby viruses.

Likewise, when dsRNA viruses enter the cell, they also use their own prepackaged RdRp to convert its negative-sense strand into a positive-sense strand that can be used as an Alka-Seltzer tablet for the same purposes as before. In all three cases, once all the genes are copied and proteins structures are assembled, the baby viruses can leave the cell and fizz away into the air, only to be inhaled by another unsuspecting host.

Reverse Transcription

Of course, there always has to be an oddball in the family. RNA retroviruses, the most famous of which is HIV, have a slightly different method by which they replicate. These types of viruses enter into the host cell's cytoplasm as before. However, in the cytoplasm, the viral RNA is converted into viral DNA using an enzyme called reverse transcriptase.

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