Viruses
Viruses are microscopic infectious agents that can only replicate inside the living cells of an organism.
They are much smaller than bacteria and cannot be seen with a light microscope.
They consist of a core of genetic material (either DNA or RNA), surrounded by a protective protein coat called a capsid.
Some viruses also have an additional outer envelope made of lipids.
Viruses cannot reproduce on their own.
They need to invade a host cell and use its machinery to make copies of themselves.
Once inside the cell, the virus takes over the host's machinery and reprograms it to produce viral components.
These components then assemble into new viruses, which can then burst out of the cell and infect other cells.
Viruses can cause a variety of diseases in humans, animals, and plants.
Some common human viral diseases include the common cold, influenza (flu), COVID-19, and HIV/AIDS.
Not all viruses are harmful, however. Some viruses can even be beneficial, such as those used in phage therapy to treat bacterial infections.
Viroids
Viroids are infectious agents even smaller than viruses, but unlike viruses, they lack a protein coat.
They are essentially short, single-stranded pieces of circular RNA (ribonucleic acid) that can infect plants and cause disease.
As mentioned, viroids are much smaller than viruses and consist only of a single strand of circular RNA.
They lack a protein coat entirely, which is a key difference between them and viruses.
Similar to viruses, viroids cannot reproduce on their own.
They need to invade a host plant cell and utilize its machinery to replicate themselves.
Once inside the plant cell, viroids manipulate the host's machinery to produce copies of their own RNA.
These new RNA molecules then fold into the characteristic circular shape and become new viroids, which can then infect other plant cells.
Viroids can cause a variety of diseases in plants, affecting their growth, development, and yield.
Some examples of viroid-induced diseases include potato spindle tuber disease, citrus exocortis disease, and avocado sunblotch viroid.
While not all viroids are harmful, their impact on agriculture can be significant.
Obelisks
Size: They are even smaller than viruses, consisting of circular RNA molecules around 1000 base pairs in length.
Shape: Their RNA folds into a rod-like structure, hence the name "obelisk."
Proteins: Interestingly, unlike viroids (another small RNA entity), obelisks can be translated into proteins called "oblins." These proteins have yet to be fully understood.
Classification: Their exact classification is still being debated. They lack the protein coat typically associated with viruses and are distinct from known viroids.
Origin and function: Scientists are still trying to understand where they come from, how they interact with their host organisms, and potential effects on human health.
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