Many of us are familiar with the concept of a species at the macro (visible) scale. Dogs are dogs; pigs are pigs, and so on. Each is a distinct species based on the fact that they can only reproduce and generate fertile offspring with other members of the same species. Over the course of many generations mutations may arise in these populations which lead to different genotypes in the species. Left long enough, these two sub-populations may keep mutating to the point where they can no longer interbreed and become their own genetically distinct species. However, when you get down to the viral scale species becomes a much more difficult concept. Viruses don’t have sex in the traditional sense, so how do we determine what makes up a viral species?
The last twenty years have been marked by a veritable explosion in sequencing technology. The Human Genome Project and it’s completion in 2003 was the crowning jewel of this burgeoning genomics revolution . The amount of information to come from this relatively new branch of science is literally mind-boggling and only grows with each passing day.
Interesting observations have come out of this massive amount of genomic data relating to the non-coding DNA in our genome. Less than 2% of the over 3 billion nucleotides in our genome are responsible for coding all of the protein that makes up a human being. This leaves a large question as to what exactly that other 98% of our genome is up to. Large parts (roughly 50%) are known as “junk DNA” with no accepted role, although new research is beginning to shed light on the functions of this DNA. The remainder of our genome is composed of long and short repeated sequences, transposons, retrotransposons and the topic of today’s article: endogenous retroviruses.
These elements are not human, they are fully viral in origin. This means that our genome is not just ours alone, we carry the DNA of many viruses that infected our ancestors in every cell in our own bodies.
Being that viruses are not technically alive in the sense that we know it they also cannot move in a self-directed manner. This is in stark comparison to some other microbes such as Schistosoma cercariae, a parasitic worm, which is capable of burrowing through intact human skin and gaining access to the vascular system within 5 minutes (1).
Thankfully viruses cannot do this, much to our benefit. Because of how they are constructed, viruses cannot mechanically move in a self-directed manner and are subject to movement solely based upon environmental interactions. Essentially, they are not only hijackers who take over cellular processes for their own good, but environmental hitchhikers as well. Continue reading How do viruses move outside the cell?
Are viruses alive?
In a sense, viruses are molecular hijackers bent on subverting host defenses, taking over a host cell’s ability to control nucleic acid and protein processing functions, and making copies of themselves to go out and infect more cells.
Viruses don’t divide like cells, don’t generate their own energy, and are fully dependent on host cells and their proteins to replicate.
Don’t let this simplicity fool you though, viruses have very sophisticated means of taking over cells and turning them into factories for making even more viral copies. However, since viruses are not capable of accomplishing many of the major of functions of life on their own outside of the host cell it has been debated for many years whether viruses are actually “alive.” Continue reading Are Viruses Alive?