Dna: The Genetic Material: Fill & Download for Free

Not all viruses are the same. In fact, while we tend to think of “viruses” as being similar to each other, two different viruses can be more different from one another than any two multicellular animals.Coronavirus and variola virus (the virus that causes smallpox) are more different from each other than an ostrich is from a marmoset.In particular, the variola virus is a DNA virus, whereas coronavirus is an RNA virus. RNA viruses tend to mutate easily, because they have their entire genome in a single strand of genetic material. DNA viruses, all other things being equal, are far more stable, because double-stranded DNA has two copies of the genetic information, one on each strand, so a single point mutation creates a spot where the two strands don’t mesh correctly.

Take a step back and look at the question. If a poison—cyanide, say—is not alive, how can it invade a cell?Something doesn’t need to be alive to get inside a cell. Non-living things get into cells all the time. Oxygen. Nutrients. Poisons. Cells have machinery—receptors on the surface, ion channel gates, that sort of thing—to bring stuff into them.Nearly everything that enters a cell isn’t alive.A virus is just a little snippet of DNA or RNA inside a shell. That’s it.Now normally you can’t get DNA or RNA from outside a cell into a cell. The molecules are way too big. But the protein shell around the DNA or RNA has a receptor that fits into receptors on the cell, where it opens a passage from the outside to the inside. A lot of textbooks on viral chemistry use a lock and key metaphor, and it fits pretty well, though I think of it more like a docking ring. The virus attaches to a docking ring on a cell and opens a hatch that allows its DNA or RNA to enter.Once the genetic material is inside, it’s game over. Your cells don’t have a way to recognize “this is our genetic material” from “this is viral genetic material.” There’s no such thing as “human DNA” or “virus DNA” from a cell’s perspective. The machinery in your cell sees DNA or RNA, it runs it, just like if a computer sees machine code, it runs it.

There are parts of your DNA that were once parts of viruses.Retroviruses are types of viruses that insert their genetic material into the genome of their host cell. Then, the genetic integrated viral material will use the cell’s machinery to create new copies of the virus. Most retroviruses infect somatic cells, which play no role in reproduction, however, a retrovirus can sometimes (it’s really rare actually) infect a germinative cell, like a spermatozoid. In the unlikely case that this spermatozoid is the one to fecundate the egg, the organism developed will carry the viral genome in all of its cells.While it is unclear how those viral parts (called Endogenous Retroviruses, ERVs) became fixed to our DNA, the most accepted theory is that retroviruses infected our evolutionary ancestors, and evolution brought them to our Homo sapiens genome.However, these viral genetic segments, albeit of signicant proportion in the genome, comprising 5%-8% of it, are now mostly defective, permeated by mutations which make them harmless.Now, if you think this is kinda cool, prepare to have your mind blown…Have you ever heard about the 1% difference between the human genome and the chimpanzee genome? If so, have you wondered, if those genomes are so alike, why are we so different from apes?One of the reasons for that is the difference in some of the regulatory regions of the genome. Much of the genetic material (in many species) is not actively coding, they are there just to control the expression of other parts. In other words, although having 99% identical DNA, humans have regulatory mechanisms, that modulate the expression of the genetic material, in a lifelong process that starts in the embryo, making us different from chimpanzees.And guess what? Among the regulatory regions that are likely responsible for that, many of the are ERVs. That’s right, the viral parts that penetrated into ours ancestors thousands of years ago.Conclusion: The human DNA segments that were once parts of viruses have probably played an important role in human evolution.PS: I’m not sure if this is the BIGGEST MINDFUCK EVER, but it certainly was a big one for me. The first time I heard about it, I was totally mindblown. It was actually one of the things that made me pursue education in a biologics area.I wrote this answer doing a lot of research to fill in the gaps time made in my memory about this. If any Quora user has a deeper knowledge in this particular subject, please comment and I will love to read about.I really recommend this article about it, for further reading:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2448423/pdf/CFG-03-494.pdf