Viroids common in high school biology

The four special viruses of prions, viroids, satellite viruses, and satellite nucleic acids are not required to be mastered in high school.

1. DNA viruses.

Double-stranded DNA viruses (positive strand of DNA + negative strand of DNA).

Replication: DNA duplex Progeny DNA duplex.

Expression: DNA negative-strand mRNA proteins.

Examples: Escherichia coli T4 bacteriophage, hepatitis B virus.

Single-stranded DNA viruses (positive strands of DNA).

Copy: DNA positive strand DNA negative strand Progeny DNA positive strand.

Expression: DNA negative-strand mRNA proteins.

2. RNA virus.

Double-stranded RNA virus (positive + negative RNA).

Replication: RNA duplex Progeny RNA duplex.

Expression: RNA negative strand mRNA proteins.

Positive single-stranded RNA viruses (RNA positive strands).

Replication: RNA positive strand RNA negative strand Progeny RNA positive strand.

Expression: RNA positive strand can be used as mRNA proteins.

Examples: Tobacco mosaic virus, atypical pneumonia virus.

Negative single-stranded RNA viruses (RNA negative strands).

Replication: RNA negative strand RNA positive strand Daughter RNA negative strand.

Expression: RNA negative strand mRNA proteins.

Examples: Epidemic ** virus, rabies virus.

3. Retroviruses (RNA positive strands).

Copy: RNA positive strand DNA negative strand DNA positive strand DNA double strand daughter RNA positive strand.

Expression: RNA positive strand can be used as mRNA proteins.

Case in point: HIV.

4. Others (subviral factors).

Viroid (RNA single-stranded).

Replication: RNA single-stranded Anti-RNA single-stranded Progenitor RNA single-strand.

Prions (proteins).

Replication: Viral protein + normal protein Viral protein + progeny viral protein.

Examples: sheep scrapie virus, bovine spongiform encephalopathy virus.

Satellite virus (nucleic acid + protein, genomic defect, helper dependent) replication: satellite virus nucleic acid Satellite virus nucleic acid.

Expression: Satellite virus mRNA protein A

Helper viral mRNA protein B

Protein A + Protein B Satellite Virus Protein.

Example: Hepatitis D virus (hepatitis B virus dependent).

Satellite nucleic acid Viroid (RNA, parasitic inside helper virus) replication: Cannot replicate independently and must rely on helper virus to replicate.

Prions. Mad cow disease virus (protein), this is the one in high school, there is no requirement for the virus-like, you are a junior in high school, ask this.

A virus is not really a living organism. Viruses are not cellular organisms and do not have a cellular structure. A virus is just a lump or a strip of DNA or RNA wrapped around a protective coat protein, and that's it.

Some viruses have some accessory structures, but none of them belong to the cellular structure. So viruses do not belong to cellular organisms. Sometimes, viruses are also referred to as molecular organisms.

Concept and classification of viruses.

Viruses are microorganisms, their structure is very simple, there is no way to complete the process of self-replication, they need to use the host cell, the use of host nutrition to complete the viral replication. The virus can infect humans as well as many other animals.

There are many viruses that cause human infections and can cause respiratory tract lesions, such as cold viruses and influenza viruses. In addition, it can cause liver lesions, such as hepatitis B virus and hepatitis C virus, and can also cause lesions of the central nervous system, such as a variety of enteroviruses that cause meningitis and pancreatic islet virus that causes encephalitis. In conclusion, viruses are diverse and can cause damage to many parts of the body.

Viruses are living things. Biology is a collective term for animals, plants, fungi, bacteria, viruses, etc. If living things are divided into six kingdoms, they can be divided into the plant kingdom, the animal kingdom, the protist kingdom, the prokaryotic kingdom, the fungal kingdom, and the non-cellular kingdom (virus).

A virus, on the other hand, is a non-cellular organism that contains only one nucleic acid (DNA or RNA) and must parasitize in living cells and replicate at the time.

Viruses can only parasitize inside the cells of other organisms. Depending on the cells they parasitize, viruses can be divided into the following three categories:

Plant viruses: specifically parasitic in human and animal cells, such as influenza viruses;

Plant viruses: specifically parasitic in plant cells, such as tobacco mosaic virus;

Bacteria and viruses: Specifically parasitic in bacterial cells, also called bacteriophages, such as E. coli phages.

A virus is a small, simple non-cellular organism that contains only one nucleic acid (DNA or RNA) and must parasitize and replicate in living cells.

Viruses are non-cellular life forms, which are composed of a long chain of nucleic acids and protein shells, and viruses do not have their own metabolic organs and no enzyme systems. As a result, when the virus leaves the host cell, it becomes a chemical substance that has no life activity and cannot reproduce on its own. Its ability to replicate, transcribe, and translate is carried out in the host cell, and when it enters the host cell, it can use the material and energy in the cell to complete life activities, and produce a new generation of viruses like it according to the genetic information contained in its own nucleic acids.

Viruses are not only divided into plant viruses, animal viruses and bacterial viruses. Structurally, it is also divided into: single-stranded RNA virus, trace-sensitive double-stranded RNA virus, single-stranded DNA virus and double-stranded DNA virus.

The life process of the virus is roughly divided into five steps: adsorption, injection (genetic material), synthesis (reverse transcription and integration into the host cell DNA), assembly (use of host cell transcription RNA, translation protein reassembly), and release.

Because viruses will shorten the distance between cells, it is easy for cells to fuse to form multinucleated cells, and then lyse.

DNA viruses include bacteriophages, smallpox virus, and hepatitis B virus (cauliflower mosaic virus, but not in the college entrance examination). RNA includes tobacco mosaic virus, HIV, SARS virus, avian influenza virus. Well, these are the types of viruses that are tested in the college entrance examination.

Seeing that you are useful, by the way, I will send something with it, there is also a protein virus, called Ruan virus, which is composed of proteins with mutated spatial structures. Another virus is a virus-like virus that consists only of RNA and does not have a protein coat.

It's good to know so much, there are so many types of college entrance examinations, you don't need to know too much, you will mix.

Well, remember to give points.

1) Cell-free structure, does not belong to prokaryotes and does not belong to eukaryotes.

2) It is parasitic and needs to be parasitic in the host cell to survive.

3) The genetic material is DNA (e.g., bacteriophage virus), or RNA (e.g., HIV, tobacco mosaic virus).

4) RNA viruses mutate more frequently.

5) Proliferation mode: replication proliferation.

6) Ingredients in the ecosystem: consumers.

7) Application: It can be used as an engineering-based carrier; It can be used as an inducer of cell fusion in animal cell fusion (e.g., inactivated Sendai virus).

Depending on the host (parasitic organism) of the virus, viruses are classified into plant viruses, animal viruses, and bacterial viruses.

Viruses that parasitize in animal and human cells are called animal viruses, such as hepatitis virus, influenza virus, HIV, rabies virus, pneumonia virus, etc.;

Viruses that specifically parasitize plant cells are called plant viruses, such as tobacco mosaic virus, tulip crushed flower virus, garlic E virus, etc.;

Viruses that specifically parasitize bacteria are called bacterial viruses (also called bacteriophages), such as E. coli phages.

To put it simply: viruses are a kind of microorganisms that do not have a cellular structure and have life characteristics such as genetics and replication.

Definition: A parasite that specializes in intracellular survival consisting only of nucleic acids (DNA or RNA) and protein shells. It has no cellular-structure and is a delicate pathogen.

Its main features are: The body is extremely small and can generally pass through the bacterial filter, so the virus is called "filtered virus" and can only be observed under an electron microscope

There is no cell structure, and its main components are only nucleic acids and proteins, so it is also called "molecular biology".

Each virus contains only one nucleic acid, either DNA or RNA;

There is no productive enzyme system, no protein and nucleic acid synthase system, and can only use the ready-made metabolic system in the host's living cells to synthesize its own nucleic acid and protein components;

The assembly of "elements" such as nucleic acids and proteins to achieve their mass reproduction;

Under the condition of in vitro, it can exist in the state of inanimate biological macromolecules, and maintain its infection vitality for a long time; Not susceptible to general antibiotics but sensitive to interferon;

The nucleic acids of some viruses can also be integrated into the host's genome and induce latent infection.

Special case: In 1997, the Nobel Prize in Physiology and Medicine-winning American biochemist Stanley Prusiner discovered a new type of organism - prion (piron). A large number of experimental studies over the years have shown that it is a group of proteins that have not been able to detect any nucleic acids so far, and the process of replication is not well understood using the same order of amino acids in normal cells.

It is a biological form different from bacteria and viruses, has strong resistance to various physical and chemical effects, is highly infectious, and has a molecular weight of 30,000 protein particles. For example: mad cow disease.

The particles are small, measured in nanometers, simple in structure, and strictly parasitic in order to reproduce by replication.

It can multiply, inherit and evolve, so it has the most basic characteristics of life. Its main features are: The body is extremely small and can generally pass through the bacterial filter, so the virus is called "filtered virus" and can only be observed under an electron microscope

There is no cell structure, and its main components are only nucleic acids and proteins, so it is also called "molecular biology": each virus contains only one nucleic acid, either DNA or RNA; There is no productive enzyme system, no protein and nucleic acid synthase system, and can only use the ready-made metabolic system in the host's living cells to synthesize its own nucleic acid and protein components; The assembly of "elements" such as nucleic acids and proteins to achieve their mass reproduction; Under the condition of in vitro, it can exist in the state of inanimate biological macromolecules, and maintain its infection vitality for a long time; Not susceptible to general antibiotics but sensitive to interferon; The nucleic acids of some viruses can also be integrated into the host's genome and induce latent infection.

I won't give you a copy of that large paragraph, you can see for yourself.

A biovirus in the narrow sense is a unique infectious agent that is a tiny organism that can use the nutrients of the host cell to actively replicate its own DNA, RNA, proteins, and other living materials. Viruses in the broad sense are much more complex, including viroids, viroids, and virions, where virions are only a simple ssRNA strand, and virions are enzyme-like protein molecules. Therefore, it is difficult to have a definite and clear definition of biological viruses.

Biological viruses, whether they are virulent phages or mild phages, must replicate and reproduce in living host cells, using the nucleotides and amino acids of the host cell to synthesize some of their own components from the host to assemble the next generation of individuals.

The replicating organism is released by lysing the host cell and infecting the new host cell.

Although biological viruses will bring certain benefits to humans, such as the use of bacteriophages can ** some bacterial infections; The use of insect viruses can prevent some agricultural pests and diseases, but they are very harmful, such as HIV, rabies virus, etc., which bring danger to human life; Influenza viruses, hepatitis viruses, etc. can bring diseases; TMV, Potato Y virus causes property damage to people.

Prions, also known as protein infecting factors, virulences, or infectious proteins, are a class of small molecule non-immunophobic hydrophobic proteins that can infect animals and replicate in host cells.

Prion virus is not strictly a virus, but a class of self-replicating and infectious factors that do not contain nucleic acids and are composed only of proteins. (Strictly speaking, prions do not replicate themselves because they do not have DNA or RNA.) Here's how it is reproduced:

Prions (SC PRP type proteins) come into contact with the normal C type PRP protein in the organism, causing the C type to become SC type.

The specific activity and replication mechanisms of prions are not well understood.

It is presumed that prions are composed of only proteins and no nucleic acids. One theory is that prion proteins can encode genetic information for themselves. This hypothesis is contrary to the "central law" of traditional molecular biology, because prions do not have nucleic acids.

Therefore, it has been hypothesized that the possible method of prion replication is that the DNA or RNA encoded by the prion is produced through the reverse translation process (in the latter case, reverse transcription is also required), and there must be a reverse transcriptase. The second is protein-guided protein synthesis, that is, the protein itself can be used as genetic information. Until then, scientists thought that all pathogens had replicationable nucleic acids (bacteria, viruses, etc.).

What most intrigues and concerns scientists today is the replication mechanism of prions. As a prion is a molecular organism that contains only proteins and no nucleic acids and can only survive inside the parasitic host cell. Therefore, it is possible that the information required to synthesize prions is present in the host cell, and the role of prions is only to activate the genes encoded for prions in the host cell, so that the prions can replicate and reproduce.

The researchers have discovered a breakthrough: this infectious agent is mainly made up of a protein called PRP. This protein can be found on the plasma membrane of the cell (the exact function is not yet understood), but it is slightly different in shape from the normal factor PRPSC, which is infectious.

Scientists speculate that this distorted protein causes normal PRPCs to be transformed into infectious proteins, a chain reaction that causes both normal proteins and disease-causing protein factors to become material for new viruses. After this hypothesis was proposed, the genes that produced PRP were extracted, and the mutated genes that produced different shapes were successfully defined and replicated, and the results of the study of laboratory rats supported this hypothesis, and the evidence is strong, but not incontrovertible. Further studies have found that prion proteins are encoded products of normal cell genes in humans and animals (the human gene is located on the short arm of chromosome 20).