This video, we're going to begin our introduction to viroids. Now, viroids, like viruses, are also obligate intracellular parasites that must infect a living cell and be inside of the cell to replicate. Unlike viruses that are made up of DNA or RNA as well as protein and sometimes lipids, viroids are only made of a single short strand of RNA that forms a closed ring. Viroids are only known to infect plants and cause plant diseases. They are not known to infect other groups of life other than plants, and there's not much known about how viroids originated or how they can cause disease in plants. Therefore, they are under investigation, and there is a lot of research to find out more about these viroids.
Now, if we take a look at our image down below of the viroids, what you'll notice is we're showing you this red structure here which is representing the circular single-stranded RNA, which we call the viroid. Notice that it is able to base pair with itself, but it is going to complete a circle here, a closed ring. It can infect plants and cause plants to wilt and ultimately die.
Down below what you see right here is another example of a viroid, specifically potato spindle tuber viroid or PSTV, which is a viroid that infects potatoes. It can infect normal potatoes and cause the potatoes to become PSTV potatoes or potatoes that have been infected by the potato spindle tuber viroid. This here concludes our brief introduction to viroids, these single short strands of RNA that form a closed ring and are obligate intracellular parasites. Once again, we'll be able to talk more about viroids later in our course. This is just the introduction. So, I'll see you all in our next video.