In the vast world of biology, there are many fascinating things occurring in nature that scientists strive to give explanations to. Anything occurring in the natural world, on any level, is a question begging to be answered. Viruses are endlessly intriguing and provoke a continuing field of research. They are considered non-living, yet what they have the ability to do is as amazing as it is creepy. Sal Khan states,
“In my opinion, viruses are, on some level, the most fascinating thing in all of biology. Because they really blur the boundary between what is an inanimate object and what is life.”
Viruses are small particles consisting of genetic information inside of a protein (Khan). This genetic information can either be RNA or DNA (Khan). Covering the nucleic acid is a protein coat called a capsid (Mandal). Sometimes a virus will have a lipid membrane on the outside of the capsid called an envelope. The complete particle is known as a virion (Mandal). Left to themselves, viruses do not do much (Khan). They do not grow or metabolize things (Khan). This alone disqualifies them from being considered a living organism (Khan). They do not have organelles, so they cannot reproduce on their own (Khan). To replicate, a virus must have a host (Khan).
A virus begins to resemble a living organism when it attaches to a cell (Khan). This cell could be a plant, bacteria, or animal cell (Khan). There are several ways a virus can infiltrate a cell (Khan). A virus can trick a cell into swallowing it allowing the virus inside the cell (Khan). Another method is endocytosis, but it is not specific to viruses (Khan). Some viruses do not enter the cell at all (Khan).If a cell has a hard outer shell, the virus will inject its genetic material into the cell (Khan). The RNA then has to capability to hijack the cell and begin coding what it functions it wants the cell to perform (Khan). The virus uses the cell’s machinery to replicate and turns it into a virus-making factory. Once the resources of the cell have been depleted, the virus and all of its copies exit the cell (Khan). The cell lyses (Khan). The cellular membrane dissolves, or disappears (Khan). This is just one example of how a virus might work. There are still many things about viruses scientists have yet to discover (Khan). The virus can also bud (Khan). When a virus buds, it pushes against the cell and it takes a section of the membrane along with it (Khan). Then the virus might not necessarily look like a foreign particle to the next cell it meets and infects because it has a piece of that cell’s membrane wrapped around it (Khan). It is like the virus is in disguise.
Not only can a virus hijack the DNA of an organism, it can also change the DNA (Khan) Instead of just making copies of itself, the virus goes into the nucleus and alters the DNA of that cell by combining its own DNA or RNA with the cell’s DNA (Khan). Each time the cell undergoes mitosis, the new cells will contain the viral genetic code, and they will pass them onto the new cells. (Khan) The HIV virus is a common example (Khan). HIV is a type of retrovirus (Khan). The virus contains RNA and a protein in it, but the protein originated from a different cell (Khan). They carry what is called a reverse-transcriptase with them into the new cell, and it codes the RNA into DNA (Khan). It merges that DNA into the host cell and alters the genetic makeup of the organism (Khan). The virus becomes a part of the organism’s DNA (Khan). When this happens, it is called a provirus (Khan).
Though there are many variations of viruses, they all go through similar, basic steps called the lytic cycle (Compton). In the lytic cycle, the virus enters the cell and hijacks the cell’s machinery to make copies of itself almost immediately (Compton). The cell lyses from the pressure, and the new virus particles exit the cell to infect more cells, as explained earlier (Compton). There is also another cycle, a more complex and patient one, called the lysogenic cycle (Compton). In this cycle, a small number of copies are made at a time and released into the environment (Compton). The host cell will stay alive along with the virus (Compton). The virus becomes a provirus if it undergoes the lysogenic cycle (Compton). An environmental change or switch can always cause the lysogenic cycle to turn quickly into the lytic cycle (Compton). The main difference between the two cycles is that the virus in the lytic cycle produces copies quickly, and the provirus in the lysogenic cycle does not (Compton).
A virus could potentially infect germ cells, which produce gametes (Khan). Gametes are sex cells (Khan). Gametes are combined in the process of fertilization to produce offspring (Khan). If the parent had infected germ cells, then its offspring will carry that viral DNA and pass it on (Khan). Sal Khan states that five to eight percent of the human genome is from retroviruses that incorporated themselves into the human germ line. The name for this is endogenous retroviruses (Khan). This means that five to eight percent of human DNA comes from viruses.
Viruses can be as extreme and life-threatening as Ebola or Zika (Khan). They can also be the reason a nose is runny or why a throat is sore (Khan). Viruses cause the common cold and flu as well as chicken pox (Khan). Viruses are microscopic particles that have big capabilities, and they blur the boundary between what is alive and not.
Works Cited
- Compton, Shannon. Study.com. n.d. 25 August 2017. study.com/academy/lesson/lysogenic-cycle-of-a-virus-definition-steps-quiz.html.
- Khan, Sal. KhanAcademy.com n.d. August 25 August 2017. http://www.khanacademy.org/science/biology/biology-of-virus-biology/v/viruses.
- Mandal, Dr. Amanda. News-medical.net. n.d. 25 August 2017.https://www.news-medical.net/health/What-is-a-Virus.aspx.