Battle and coexistence between humans and viruses | Science Gallery

A global virus pandemic has almost overturned people's previous lifestyles, and has also made viruses, a special life form, have a strong sense of "presence" in our lives. Although viruses are an inevitable part of life, most people still know very little about them. Today, let us learn about them together!

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More viruses than stars

When it comes to viruses that we have encountered or heard of in our lives, everyone can list a few. But when asked how many viruses there are in the world, many people do not have a clear idea.

So, how many viruses exist on this blue planet we live on?

Scientists estimate that there are at least 1031 virus particles on Earth, far more than the number of stars in the universe (about 1024). As the world-renowned popular science writer Carl Zimmer described in his popular science work "Virus Planet", "Earth is a virus planet."

The long-awaited

Viruses not only exist in every corner, but are also a very ancient life form. As early as the Eastern Han Dynasty, there were records of cases of smallpox virus infection in the classics. However, humans have only known viruses for more than 100 years.

In 1892, Russian biologist Ivanovsky discovered during his research on tobacco mosaic that the extract of infected tobacco leaves was still infectious after filtration. However, influenced by the mainstream atmosphere of bacterial pathogenicity at the time, he did not realize the existence of viruses, but believed that this phenomenon was caused by toxins secreted by bacteria.

Normal (left) and tobacco leaves with tobacco mosaic disease (right)

Source: Biology, Grade 8, Vol. 1, People's Education Press

In 1898, after repeated experimental verification, Dutch microbiologist Beijerinck pointed out that tobacco mosaic disease was caused by an organism that was too small to be observed under an ordinary microscope and was different from bacteria, and named it virus. After the official name, researchers have successively isolated and discovered many viruses, but due to the lack of technical means to observe viruses, people still do not know what kind of organism viruses are. Some scholars even believe that the essence of viruses is a protein.

Later, British scholars Bowden and Peary discovered the presence of nucleic acids in the extract of tobacco mosaic virus. At this point, the scientific community finally came to a unified conclusion: viruses are composed of proteins and nucleic acids, and nucleic acids are the main reason for the infectivity of viruses.

It was not until the invention of the electron microscope that the German scientist Kausch directly observed the "true appearance" of the tobacco mosaic virus under an electron microscope for the first time - a long rod-shaped particle with a diameter of 15 nanometers and a length of 300 nanometers.

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Viruses are composed of a protein shell and a nucleic acid (DNA or RNA) wrapped inside. They do not have a cell structure, nor do they have complex organs and systems. Compared with other organisms, they are more like a simple puzzle toy, but they can perform life-specific activities such as proliferation and evolution after invading living cells. It can be said that this discovery overturned the definition of life in textbooks at the time.

Not all viruses infect humans.

Whether it's the influenza virus that "regularly harasses" us every year, the AIDS virus that makes people turn pale at the mention of it, the rabies virus that is fatal once infected, or the new coronavirus that continues to add trouble to our lives... when you count them up, we seem to be living in a world full of viruses.

However, not all viruses infect humans. In fact, viruses are very "picky" about the cells they infect. Each virus has a special receptor binding protein on the surface of its protein shell. Only when the cell surface has a receptor that can bind to this binding protein can the virus infect the host cell and release its genetic material into the cell for replication. Depending on the host, viruses can be divided into animal viruses, plant viruses, and microbial viruses that specifically infect microorganisms.

Moreover, not all viruses are harmful to the human body. Studies have shown that the number of viruses on the human body and in the body is about 10 times the number of bacteria. There are more than 140,000 viruses living in the intestines alone, but most of them can coexist with humans without causing disease. Not only that, viruses also play an irreplaceable role in fields such as biological control and genetic engineering.

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Everyone has a virus in their body

What is even more unexpected is that even if we have been living in a completely virus-free environment, there are indelible traces of viruses in our bodies. These are remnants of ancient viral genomes, accounting for about 8% of human genome DNA. As research deepens, scientists have discovered that these genetic remnants from viruses play a very important role in the pluripotency and development of human liver cells.

Many viruses not only infect different species, but also transmit DNA fragments between different species, providing new genetic material for biological evolution.

The fight between humans and viruses seems to be an endless struggle. However, as research continues to deepen, some scientists have begun to consider how humans should coexist peacefully with viruses on this earth.

As scientists from the Global Virus Project said, "When you consider how every animal, plant, and microorganism has been shaped in the process of evolution, you must consider the influence of tiny but powerful viruses." Perhaps, many years later, when people look back at this global epidemic caused by the new coronavirus, they will have different feelings than we do now...

Creative team: China Science and Technology Museum New Media Team

Review expert: Gu Haitong, deputy chief physician of the Department of Respiratory Medicine, Beijing Tongren Hospital, Capital Medical University