Popular Science: Chinese Academy of Sciences

Bacteria size under a microscope. Institute of Microbiology, Chinese Academy of Sciences. China News Service, Beijing, January 31 (Reporter Sun Zifa) At present, the outbreak of pneumonia caused by a new type of coronavirus has caused widespread concern. The public will also hear the message that there are no special drugs at the same time when they are doing a good job in protecting themselves. Will ask: What are the similarities and differences between viruses and bacteria? Why can’t it be treated with antibiotics? Why can’t we kill viruses with antibiotics?

In response to these problems and doubts, the Institute of Microbiology, Chinese Academy of Sciences (Institute of Microbiology, Chinese Academy of Sciences) organized the scientific experts of this institute to analyze and respond to–

Are tiny creatures on earth

Experts said that bacteria and viruses are microorganisms. As the smallest form of life on the planet, people always ignore their existence, but this tiny creature is always brushed with “existence.” Be infected by them.

Bacteria are cells with cell walls, DNA, and organelles. They can produce the enzymes needed for synthesis and metabolize, and can divide and reproduce on their own. The virus is much smaller than the bacteria. The main structure is the protein capsid and the internal genetic material (DNA or RNA), and the virus cannot replicate itself. The virus needs to infect host cells to replicate its own genetic material, and then release more progeny viruses to infect other host cells.

Bacteria can be harmless or even beneficial to human health, and they can survive independently. The purpose of the virus is to replicate itself, so it does not exist without infecting the host. It is the purest “selfish gene”.

The size difference between the two is about 1000 times

Experts from the Institute of Microbiology, Chinese Academy of Sciences said that bacteria in a broad sense are prokaryotes. Although they have a cell structure, they are still very different from human cell structures. They have a simpler structure. Bacteria are generally spherical, rod-shaped, spiral-shaped, etc. When people name it, do not forget to add a description of the shape, such as E. coli, Lactobacillus, Staphylococcus aureus, etc. shape).

The smallest bacteria currently known are only 0.2 micrometers long, so they can only be seen under a microscope. The largest bacteria in the world can be seen directly with the naked eye, 0.2-0.6 mm in size, and is a type of sulphurophilus Namibia bacterial.

A virus is a non-cellular form composed of a nucleic acid molecule (DNA or RNA) and a protein. It is an organic species between living and non-living organisms that lives by parasitism. It replicates the DNA that appears after entering the cell. Waiting for metabolism is indeed a characteristic of living beings, and after leaving the cell it is just a lifeless crystal.

Most viruses have a diameter of 10-300 nm (nanometers), and some filamentous viruses can reach a length of 1400 nm, but their width is only about 80 nm. Most viruses cannot be observed under a light microscope, and scanning or transmission electron microscopy is the main tool for observing the morphology of virus particles. Compared with viruses and bacteria, the size difference between the two is about 1000 times. Illustration of virus replication. Institute of Microbiology, Chinese Academy of Sciences

Different invasion methods

Scientists say that there are many “good people” in bacteria. Among them, saprophytic bacteria are important decomposers in the ecosystem to enable the carbon cycle to proceed smoothly; some bacteria will perform nitrogen fixation to convert nitrogen into bioavailable forms. The production of cheese and yogurt and wine, the manufacture of some antibiotics, and the treatment of wastewater are all related to bacteria. Bacteria are also widely used in the field of biotechnology. Of course, the “bad people” in bacteria are many pathogenic bacteria, including tuberculosis, anthrax, plague and other diseases are caused by bacteria.

Bacteria and the human body are mainly parasitic. As far as pathogenic bacteria are concerned, since most bacteria have their own metabolic systems, bacteria can invade normal human cells after they have invaded the human body. Bacteria capture the necessary nutrients of the body; the growth of bacteria produces a variety of metabolites that disrupt the body’s physiological balance; even the volume of bacteria has become a pathogenic factor that interferes with and destroys cell functions. Therefore, in In some diseases, the proliferation of bacteria alone can have fatal consequences.

The virus may invade the body from a sneeze or a physical contact. The virus needs to be parasitic in a living host cell, and it depends on the host cell to provide the raw material system, energy and place required for the virus replication process. When a virus is ready to infect host cells, it needs the following six steps to complete its proliferation activities: adsorption, invasion, husking, biosynthesis, assembly, and release.

Adsorption: The virus “sees” target cells by recognizing receptor protein molecules specific to the surface of the host cell membrane (such as the new coronavirus that recognizes angiotensin-converting enzyme 2-ACE2 on the surface of human respiratory and lung cells); invasion: Then the virus either enters the host cell by some means (such as membrane fusion), or directly injects genetic material into the host cell; husking: immediately after the viral infectious nucleic acid is released from the capsid; biosynthesis: “Non-stop” To carry out biosynthesis—according to genetic instructions and using the raw materials, energy and place provided by host cells to synthesize virus nucleic acids and proteins; assembly: newly synthesized viral nucleic acids and proteins will be assembled into progeny viruses; release: progeny virus release Outside the host cell.

Human defense and counterattack

Experts point out that both bacteria and viruses must break through the human body’s defenses to complete the invasion, but the human body will eventually find their existence, and the human immune system has its own protective measures and early warning mechanisms.

The first line of defense: skin and mucous membranes. The first way humans protect themselves is defense. The skin and mucous membranes form a relatively closed system for the human body. When harmful substances are about to invade the human body, the skin and mucous membranes block external pathogenic factors outside the body.

Second line of defense: bactericidal substances and phagocytic cells. There are always germicidal substances and phagocytes on the mucosal surface and inside the human body to “patrol” to prevent the invasion of pathogens. Take lysozyme as an example, it can destroy the cell wall of bacteria, cause the ruptured contents of the cell wall to escape and dissolve the bacteria. It can also directly bind to negatively charged viral proteins and form double salts with DNA, RNA and apoproteins. Inactivate the virus. Therefore, the enzyme has antibacterial, anti-inflammatory and antiviral effects.

Third line of defense: Specific immunity. When powerful pathogens break through the first two lines of defense, the human body’s counterattack has just begun. Through the phagocytosis of phagocytes and the analysis of special immune cells (T cells), the body produces antibodies that can specifically recognize invaders. Antibodies can cause pathogens to stick together and are no longer invasive, and eventually exposed to the cells. Pathogens will be killed. But is the virus that invaded the cell safe? No! The human body can subtlely identify which cells are infected by the virus, and then send a “killer” to kill the infected cells, releasing the virus inside the cell for the antigen to be destroyed.

However, the human body’s counterattack takes time to prepare, and pathogens will invade through this time interval and occupy the human body.

Drug therapy aid

Bacterial infections once became the greatest enemy of mankind. For example, the plague was called the “black death” in Europe that year, which once reduced the European population by one third in three years; China now also lists plague and cholera as a class A infectious disease.

It was not until the discovery and promotion of antibiotics that humans controlled the outbreak of bacterial infections.

Antibiotics have a killing effect on bacteria. By destroying the structure of bacterial cells, such as cell walls, cell membranes, changing internal metabolism, and hindering nucleic acid and protein synthesis, the purpose of killing bacteria is achieved.

However, antibiotics are not effective against viruses because the structures of bacteria and viruses are completely different.

Because bacteria have cell walls, and their own nucleic acid replication machinery and ribosomes, antibiotics designed to target these targets can guarantee the killing of bacteria with minimal side effects on humans. However, the virus has no cell wall, no own nuclease, and no ribosome. All its functions depend on the host cell to perform, so antibiotics cannot kill the virus.

The ideal antiviral drug is that it can act on one or several links of the virus appreciation cycle and interfere or block it without affecting the normal metabolism of the host cell. For example, the common drug ribavirin provides a large number of nucleotide analogues, replacing the normal nucleotides by stealing the column, making the virus lose its ability to replicate, and it has the effect of inhibiting virus amplification (but it also has great side effects on the human body). In addition, the anti-flu drug oseltamivir works by blocking the release of progeny viruses.

In response to the epidemic, researchers at the Wuhan Institute of Virology and the Academy of Military Medical Sciences of the Chinese Academy of Sciences have also initially screened at the cellular level for Remidiv or Remdesivir that has a good inhibitory effect on the new coronavirus (2019-nCoV) , GS-5734, anti-Ebola drug phase II clinical), chloroquine (Chloroquine, Sigma-C6628, antimalarial drug), ritonavir (Ritonavir, anti-HIV drug).

Scientists reminded that in the face of virus treatment, humans have never found universal drugs like antibiotics. Active treatment is to mobilize the body’s own immune capabilities to fight the virus, because only the organism itself really knows how to fight the organism.

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