Strictly speaking, is a virus a creature? How are protein viruses (such as prions) replicated?

Virus is a special kind of organism, but it does not belong to the structural level of life system (the smallest unit of the structural level of life system is cell, and virus has no cell structure).

Viruses are generally parasitic, so they cannot complete their life activities independently.

The metabolic process of virus is actually its own proliferation process.

Protein is the only prion without nucleic acid. Prions are tiny organisms. It has no cell structure and its composition is very simple. Generally, it only has a shell composed of protein and a nucleus composed of nucleic acid. Nucleic acid (DNA or RNA) plays an important role in the inheritance of virus, while protein shell only protects nucleic acid, but does not inherit it. This is people's basic understanding of viruses. However, with the in-depth study of some diseases, scientists found that there is another organism different from the general virus. It has no nucleic acid only in protein, but it is contagious and hereditary at the same time, with unusual characteristics different from all known traditional pathogens. This is a prion. 1. The discovery of prions as early as 300 years ago, people have noticed the "itching disease" of sheep and goats. Its symptoms are: loss of coordination, instability, irritability, itching, and even paralysis and death. In 1960s, British biologist Alpine destroyed DNA and RNA by radiation, but its tissues were still infectious. Therefore, it is considered that the pathogenic factor of scrapie is not nucleic acid, but protein. Because this inference did not conform to the general understanding at that time and lacked strong experimental support, it was not recognized and even regarded as heresy. 1947 found mink encephalomalacia with symptoms similar to "sheep scratching injury". Later, chronic wasting diseases (atrophy) of red deer and deer and spongiform encephalopathy of cats were discovered one after another. The most shocking thing is that 1996 spring "mad cow disease" caused unprecedented panic in Britain and even the whole world, and even triggered political and economic turmoil. For a time, people "talk about the color change of cattle." From 65438 to 0997, the Nobel Prize in Physiology and Medicine was awarded to Stanley B.P Prusiner, an American biochemist, for his discovery of a new type of organism-Piron. 2. The nature and structural cycle of prions. After years of research, Daniel Prusiner finally figured out some characteristics of Ruan virus, the pathogen that causes itching. He found that Nguyen virus was only 30-50 nanometers in size, and the structure of virus particles could not be seen under electron microscope. After negative staining, aggregated rod-shaped bodies with the size of about 10 ~ 250 x 100 ~ 200 nm will be seen. It has also been found that prions show amazing resistance to inactivation caused by many factors. It is quite tolerant to physical factors such as ultraviolet rays, ionizing radiation, ultrasonic waves and high temperature of 80 ~ 100℃. It has strong resistance to chemical reagents and biochemical reagents, such as formaldehyde, hydroxylamine and nuclease. No resistance to protease K, urea, phenol, chloroform, etc. Biologically, prions can cause chronic virus infection without showing immunogenicity, and macrophages can reduce or even inactivate the infectivity of prions. However, using immunological technology, it is impossible to detect the existence of specific antibodies and induce the production of interferon, and it is not affected by interferon.