Inside you right now are most probably millions, if not even trillions of viruses. Some viruses are extremely deadly, but the vast majority are completely benign. They can be found in almost every type of life, including plants, animals, and bacteria. Yet, viruses themselves are completely different from any other type of life form. In fact, it's debatable whether they're even life forms at all. Learn more about viruses, what they are and how they work on this episode of Everything Everywhere Daily. If you've been on the planet Earth over the last few years, you have probably become very familiar with the discussion of viruses. Yet in all the talk about viruses, seldom was there any attempt at explaining what a virus was or how they worked. So in this episode, I want to go over the basics of what viruses are, how they work, and how they were discovered. Viruses are microscopic infectious agents that can replicate only inside living cells of organisms. Viruses are made up of genetic material, either double-strand DNA or single-strand RNA, enclosed in a protein coat and sometimes in an additional lipid envelope. And lipids are just a fancy word for fats. Viruses are not made of cells themselves and are much smaller than cells.

A cell could be observed through most optical microscopes. A virus, however, can only be seen with something as powerful as an electron microscope. The fact that viruses are not made out of cells is the reason why antibiotics are ineffective against viruses. Viruses reproduce in a very unique way. First, a virus will attach itself to a specific receptor on the surface of a host cell. The receptors are literally molecules that fit together on the cell in the virus. Next, the virus or its genetic material will enter the host cell. The viral genetic material takes over the host cell's machinery to replicate itself. New viruses are assembled inside the host cell using the cell's materials as the basis for the new virus. Finally, new viruses are released from the host cell, often destroying it in the process to infect other cells. Because viruses are really just glorified strands of DNA or RNA, there is a great deal of debate as to whether viruses are in fact alive. There's no clear-cut definition as to what makes something alive, which is why there's debate about whether viruses are life forms. They meet some of the definitions of life, but they don't meet all of the definitions of life.

For starters, all life that we can positively agree upon as being alive has some cellular structure. Everything from the largest animal to the smallest single-cell life form is made up of cells consisting of a cell membrane. Viruses, as I mentioned, are not made up of cells. Another criterion for something to be alive is that it has to have some metabolism. It will have some chemical reactions that convert energy from the environment to sustain life. Viruses, however, have no metabolism. They cannot generate energy, synthesize proteins, or carry out any biochemical reactions on their own. They rely entirely on the host cell's machinery to perform these functions. Absent to host cell, they are completely and totally inert. So why then are there some people who think that viruses are alive? For starters, they're made up of genetic material, which is the basis for all life. Unlike other life forms, viruses pretty much are just genetic material and nothing more. Viruses can reproduce. They can't reproduce independently and require material from a host cell, but they nonetheless reproduce in so far as one virus can create many other identical viruses. Furthermore, viruses can evolve through natural selection. In fact, given how small they are, they can sometimes evolve very quickly.

Small mutations in a virus's molecular structure can have profound impacts and change a virus grows or develops. So you can see why there is debate about whether viruses are even alive. If they are alive, they're about as close to something not being alive as possible. And likewise, if they aren't alive, they are border aligned to becoming a life form. Another big question is how viruses arose. Did they predate cells or did they come after the creation of cells? Or did they evolve with them at the same time? And the answer is, we We don't really know. Viruses don't make fossils. However, there are multiple theories about their origin. There are three popular theories as to how viruses developed. The first is the regressive hypothesis. This holds that viruses may have evolved from small cells that were parasites to other cells. Over time, they just lost unnecessary genes and cell structures and became more dependent upon host cells until they were nothing but genetic material. The second theory theory is the cellular origin hypothesis. This theory contends that each virus may have originated from pieces of DNA or RNA that escaped from the genes of larger organisms.

Unlike the regressive hypothesis, this doesn't assume that full cells devolved, rather, bits of genetic material just got loose and began reproducing. The third theory is the co-evolution hypothesis. This hypothesis contends that viruses might have evolved alongside their host cells in the primordial soup of the on the Earth, representing ancient self-replicating molecules that developed the ability to infect cells. Personally, the co-evolution hypothesis seems to make the most sense to me, but my opinion is based on pretty much absolutely nothing. Absent discovering DNA-based life on other planets or artificially creating life in the laboratory, it's unlikely that we'll ever know the true reason. Given the nature of viruses, they were actually discovered very late. Humans had always lived alongside viruses, and they were very familiar with the effects of viruses, even if it was nothing more than the common cold. The story of viruses really begins in 1884. A researcher named Charles Chamberlain developed a porcelain filter known as the Chamberlain filter, which could remove bacteria from aquatic solutions. The Chamberlain filter was used as a water filter that could remove bacteria, then the smallest known unit of life at the time. In 1892, Dmitri Ivanovsky, a Russian botanist, used the Chamberlain filter to study a disease affecting tobacco plants.

He found that the filtered sap from deceased plants could still cause disease in healthy plants, suggesting the presence of an infectious agent smaller than bacteria. In 1898, Martienus Beierring, a Dutch microbiologist, conducted similar experiments and confirmed Ibonosky's findings. He coined the term virus, from the Latin word for poison, to describe the infectious agent and concluded that it was a new type of pathogen that could replicate in living cells. In 1901, American Army Physicist and Medical Researcher Walter Reid and his colleagues demonstrated that yellow fever was caused by a filterable agent and identified it as a virus, the first human virus that was ever discovered. In the succeeding years, more and more diseases were discovered that couldn't be bacteria-based. They were based on these mysterious minuscule substances known as viruses. In 1935, the American biochemist Wendell Stanley successfully crystallized the tobacco mosaic virus, demonstrating that viruses could be studied like chemical substances. This work earned him a Nobel Prize in chemistry in 1946 and provided insights into the molecular nature of viruses. The 1940s and '50s saw the rise of electron microscopes, which were finally able to see what viruses looked like. Finally, in 1952, Alfred Hershie and Martha Chase used bacteriophages to demonstrate that DNA, not protein, was the material that genes were made of, and also proved that viruses were made of DNA.

Work that was awarded the Nobel Prize in Medicine in 1969. It's believed that there are currently millions of different types of viruses that exist on Earth today, the vast majority of which have never been identified. Approximately 11,000 different types of virus have been identified and cataloged so far. Given the genetic nature of viruses, almost all viruses can only affect and reproduce with certain specific species. A virus that infects a plant cannot replicate with animal cells and vice versa. The number of different species of virus can infect is known as its host range. For example, smallpox was a disease transmitted via a virus, and it could only be transmitted from human to human. It was highly specialized and had a very narrow host range. The influence influenza A virus, on the other hand, has a much wider host range and can infect pigs, birds, and humans. Categorizing viruses is much more challenging than categorizing other life forms, given their microscopic nature. In 1966, the International Committee on Taxonomy of Viruses was created to tackle this problem. They eventually created a 15-layer system that is analogous to the system used to categorize cellular life. It goes from the highest rank of realm down known to the lowest rank of species.

Unlike traditional taxonomy, these broad realms are not based on common ancestors, but rather on shared traits. In conjunction with this system, there's another system called the Baltimore System, which was developed by the Nobel Prize-winning biologist, David Baltimore. It's a six-category system that categorizes viruses based on their genetic makeup. If it's DNA or RNA, how many strands it has, and how it replicates. There are other ways to categorize viruses as well, including their morphology and the diseases they're associated with. As you're probably aware, viruses are the cause of many serious diseases that affect humans. The common cold is caused by viruses, as are much more serious diseases, such such as influenza, HIV, Ebola, and of course, COVID-19. There is no one single means of spreading viral infections. Some viruses are spread through the air, some through water and other fluids, and some can be spread via physical contact such as shaking hands. How a virus spreads is due in large part to its morphology or its shape and structure. Many people fear deadly viruses like Ebola suddenly becoming airborne, and this is almost an impossibility. It would require mutating into something totally different in order to change its transmission vector that radically.

And if it changed that much, then it would no longer be the Ebola virus. Fighting viruses is very different than fighting bacteria. The first strategy for attacking a viral infection is to simply try and stop the spread of the virus. This involves identifying the transmission vector and then interrupting it. The second strategy is to create a vaccine, which allows the body's immune system to fight the virus. If you remember back to my previous episode on smallpox, this was the strategy behind the eradication of that disease. Widespread vaccinations, plus identifying and isolating people infected, allowed the disease to eventually be totally eliminated. The other big approach to fighting viral diseases are antiviral drugs. Antiviral drugs tend to target very specific viruses. They do so by blocking the replication zones on the virus. They may do this by having DNA fragments in the drug that viruses will latch onto instead of latching onto cells. Developing antiviral drugs can be very expensive and time-consuming, given how focused they have to be for the virus that they're targeting. There are also virucides, which are biological or chemical agents that can outright kill viruses. The problem with virucides is that they can often damage cells.

As such, virucides tend to only be used outside the body and not ingested. I should close by noting that not all viruses are bad. One of the most promising fields of medicine today is gene therapy. Gene therapy is a medical technique that involves altering or manipulating an individual's genes to treat or prevent disease. One of the primary methods of doing this is harnessing the power of a virus to insert DNA into a cell. Some gene therapy techniques involve modifying a virus such that it will transport a beneficial change directly into a cell. As of today, the majority of gene therapy trials are involved in the treatment of cancer. Viruses are an extremely large part of biology, as we know it on the planet Earth. Viruses can be found in almost every ecosystem on every corner of the planet, and some can probably be harmlessly found inside you right now. Regardless of whether you consider them to be alive or not, there is no doubt that viruses are some of the most important parts of the biological world. The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Benjie Long and Cameron Kiever.

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