It is officially flu season. Just last week, there were about 100 students at my school who had to stay home because they got the flu. And, China is currently experiencing the coronavirus. Both the flu and the coronavirus (like the name implies) are viruses.
In 1892, Dmitri Ivanovski, a Russian biologist, determined that something caused tobacco mosaic disease. He just wasn’t sure what. In 1897, Martinus Beijerinck, a Dutch scientist, named the cause of this disease “virus,” after the Latin word for “poison.” In 1935, an American biochemist named Wendell Stanley isolated crystals of tobacco mosaic disease and, since living organisms do not crystallize, he was able to infer what caused the disease was not something that lives. A virus is a nonliving particle that is made up of proteins, nucleic acids and lipids. The only way they can reproduce is by infecting living organisms.
Living organisms have seven characteristics in common: They respond to their environment, they grow and change, they reproduce, they adapt through evolution, their cells are organized (e.g. our cells become tissues, tissues become organs, organs become organ systems, organ systems become organisms), they are able to metabolize and they are able to maintain homeostasis (e.g. when we’re really hot, we excrete sweat to cool down our bodies). The biggest reason viruses aren’t considered “living” is because they can’t reproduce on their own.
Viruses are really tiny, so tiny, in fact, that a powerful electron microscope is needed to see them. Viruses basically infect their hosts by tricking them. They bind their protein with the protein receptors on cells and release their genes once they’re inside the cell.
Since viruses have such a precise way of infecting cells, they typically stick to one type of living organism — people, animals and plants, for example.
Once a virus infects a cell, it can either be a lytic infection or a lysogenic infection. A lytic infection is worse for the bacterial cell to have. It’s when the virus enters a cell, makes copies of itself and causes the cell to burst. When the virus injects its DNA (deoxyribonucleic acid, aka the genetic material of organisms) into the bacterial cell, the cell begins to make mRNA (messenger RNA (ribonucleic acid)) from the viral genes. The viral mRNA becomes viral proteins. The host cell’s metabolic system makes thousands of copies of the viral nucleic acid (genetic material) and capsid proteins. The viral DNA then becomes new virus particles.
A lysogenic infection is when the bacterial host cell is not immediately taken over. The viral nucleic acid is inserted into the host cell’s DNA and it is copied along with the host cell’s DNA but in such a way that it does not hurt the host cell. Bacteriophage DNA that is embedded in the bacterial host cell’s DNA is called a prophage. The prophage could stay a part of the cell’s DNA for generations. But, external factors such as radiation, heat and chemicals can cause the prophage to become active. If the prophage becomes active, the lysogenic infection becomes a lytic infection. Viral infections in bacteria differ a little from viral infections in eukaryotic cells (which are the types of cells we have) but, for the most part, are similar.
Viruses are parasites because they depend on other living organisms for their existence. It can be concluded that viruses developed after the first living organisms did because they’re so dependent on other living things. Stay healthy this flu season!
Vaageesha Das is a 10th grader at Morgantown High School. Today’s information comes from: https://study.com/academy/lesson/8-characteristics-of-life-in-biology.htm; 8 Characteristics of Life. Retrieved from cattle; Miller, K. R., & Levine, J. S. (2019). Biology. Boston, MA: Pearson.
