Viruses only contain nucleotides and proteins, which can cause thousands of "large" animals to get sick or even die. Viruses are small and so horrible, such as hepatitis B virus, AIDS, SARS, avian influenza and MERS recently.
In short, the virus is the simplest and smallest microorganism discovered by human beings at present, but whether the virus belongs to life or not is still controversial at present, because the virus itself cannot carry out any life activities. The main structure of the virus is that there is a piece of genetic material inside and a biofilm outside, which constitutes the simplest structure of the virus. There are obvious differences in the size of various viruses, but even so, viruses are much smaller than bacteria, such as colorectal cancer bacteria, with a diameter of about 6000 nanometers, while the largest virus, pox virus, has a diameter of about 300 nanometers, while the smallest virus, parvovirus, has a diameter of only 20 nanometers.
SARS coronavirus under electron microscope
The structure of virus
A complete and mature virus particle is called virion, which is a typical structural form of virus outside the cell and has certain infectivity. The main shape of virus body is spherical or quasi-spherical, and a few can be filamentous, rod-shaped or brick-shaped.
The basic structure of virus body is composed of core and capsid, which is called nucleocapsid. Some viruses have an envelope outside the nucleocapsid. The virus with an envelope is called an enveloped virus, and the virus without an envelope is called a naked virus.
The basic structure of virus
coreThis core of the virus is actually nucleic acid, which is what we call genetic material. At present, the genetic materials discovered by human beings are DNA and RNA, the genetic materials of human beings are DNA, and the genetic materials of viruses are both RNA and DNA. Needless to say, the importance of genetic material is that the genetic material of virus mainly provides genetic information for virus replication, inheritance and variation.
capsidThe capsid of a virus is the protein’s capsid wrapped around the genetic material of the virus. This capsid not only has a certain protective effect, but also has a certain antigenicity, which can mediate the virus to enter the host cell.
envelopeEnvelope is not a necessary structure for viruses. When the virus replicates in the host cell and is released outside the host cell by budding, the virus will take out part of the cell membrane of the host cell and form its own envelope.
Genetic material of virus
The genetic material of human and animals is DNA, which we all know. In fact, DNA is nucleic acid, and there are two kinds of nucleic acids, one is DNA and the other is RNA. In human cells, DNA is genetic material, while RNA is mainly used for transcription and translation of genetic information on NDA. The genetic material of virus has both DNA and RNA, so it can be divided into DNA virus and RNA virus.
We know that the way of virus infection is parasitism. When the virus enters the living cell, the genetic material of the virus will use the organelles in the living cell to synthesize the protein capsid for itself and copy its genetic information, and then assemble it after the copy is completed to form a new offspring virus. In this process, genetic material plays a decisive leading role.
Another important feature of virus genetic material is that it is easy to mutate, because there are not many structures that can protect the virus, and most RNA viruses are single-stranded, so single-stranded genetic material is not as stable as double-stranded DNA. This instability brings great trouble to the treatment of virus and the development of virus vaccine.
In the process of virus infecting living cells, the organelles of living cells are used to produce genetic material and protein shell for themselves, and then released to the outside of the cells.
Protein of the virus
Although genetic material is very important, its proportion is not high. protein is the main component of the virus, accounting for about 70% of the total virus. Protein of virus is the genetic material of virus synthesized by using host cells. The protein function of the virus is to protect the genetic material of the virus, participate in the infection process, mediate the virus to enter the host cell, and have certain antigenicity. The so-called antigenicity refers to the ability to cause immune cells in the host to recognize.
Classification of viruses
The discovery of viruses is much later than that of cells, and there are thousands of viruses found. At present, families, genera and species are used to classify viruses. The main basis of virus classification are:
According to the genetic material of the virus: the reference factors mainly include DNA or RNA, single-stranded or double-stranded, molecular weight and gene number;
According to the shape and size of the virus;
The symmetry of capsid and the number of capsid particles;
Whether there is an envelope;
Antigenicity;
Sensitivity to physical and chemical factors;
Biological characteristics: such as genetic mode, host range, transmission route and pathogenicity.
Pathogenicity of virus
The reason why we are afraid of viruses is that they are invisible to the naked eye and have a strong pathogenic effect. Although not all viruses can cause diseases, if some deadly viruses spread among people, the consequences will be unimaginable. Different viruses have different modes of transmission. Viruses can spread through air, droplets, contaminated water and food, contaminated blood, syringes, swimming pools, sexual contact, mother-to-child bites, mosquito bites, animal bites and other ways.
Deal with Ebola virus infected people, fully armed, and isolate the virus to the maximum extent.
The mechanisms of viral pathogenesis are as follows:
Cytotoxic effectViruses replicate by using organelles in host cells, which can replicate a large number of offspring viruses in a short time, and a large number of viruses will lead to cell lysis. This virus is common in some viruses that have no envelope and are more lethal. When the virus uses cells to replicate itself, it will interfere with the life activities of the cells themselves, leading to disorder of metabolism in the cells, resulting in pathological changes and cell death. If this cell killing effect occurs in important organs, or the infected area of the virus is relatively large, it will often cause serious consequences, irreversible sequelae and even death.
Steady state infectionAfter some viruses enter cells, they can replicate, but they will not immediately lead to cell death. The newly generated viruses slowly release their offspring by budding. This kind of infection is common in some enveloped viruses. Although this kind of virus can replicate itself after infecting cells, it will not affect the normal metabolic function of cells, nor will it destroy the lysosomes of cells, so it will not directly lead to cell lysis and death. However, the surface of infected cells will carry the synthetic protein of the virus, and the synthetic protein of the virus belongs to the antigen to the human body, so such cells will still be attacked by the immune cells of the human body, and the infected cells will still be killed.
Viruses can cause cancerThe relationship between many viruses and human malignant tumors has been confirmed, such as the relationship between HPV virus and cervical cancer. At present, the cervical cancer vaccine on the market does not directly prevent cervical cancer, but prevents HPV virus. We know that the canceration of normal cells is the mutation of genes controlling cell growth, which leads to the uncontrolled growth of cells, and the virus with carcinogenic effect can change the genes controlling cell proliferation and lead to cell canceration.
Pathological sections of virus-infected hepatocytes
On the one hand, the pathogenic effect of virus on human body comes from the direct effect of virus, and on the other hand, it is very important that virus causes the indirect effect of human immune response. If the human body releases a large number of inflammatory cells in order to kill the virus, these inflammatory cells will reach all parts of the body along the blood vessels, leading to systemic inflammatory reactions and affecting the functions of normal organs. For example, if the whole lung is full of inflammatory cells, then this person will have difficulty breathing, which will lead to hypoxia, so a vicious circle like this may endanger the life of the patient.
summary
Virus is a ubiquitous microorganism in nature, and its volume is much smaller than that of cells. Viruses can’t carry out any life activities by themselves, but must be parasitic on living cells, so viruses can’t be regarded as an independent living body. Being infected by virus does not necessarily mean that it will cause disease. There are many viruses in a healthy human body, so we should treat viruses correctly. At present, we humans still know very little about viruses, and there is still a long way to go.