This article is written by Ma Chenhao, a surgical resident at Peking Union Medical College Hospital
Why a small virus has such great power, in order to understand its function, it is necessary to start from understanding its structure, after all, the structure determines the function.
First, the structure of the new coronavirus virus
First, we need to know that the name of this virus is SARS-CoV-2. This new type of coronavirus belongs to the same category of coronavirus as SRAS.
Coronavirus is named after the obvious rod-like particle bulges that can be observed under the microscope, shaped like the crowns of medieval European emperors.
Next, take a closer look at the structure of the virus from the outside in. The outermost layer of the coronavirus has three proteins, called the spike glycoprotein, the small envelope glycoprotein (M protein), and the membrane glycoprotein (E-protein).
The spike glycoprotein mainly recognizes and binds to host cell surface receptors, and plays a key role in mediating the fusion of viral envelope and cell membrane. In layman’s terms, the spike glycoprotein is like a key, and its main function is to open the host cell’s cell membrane.
Next, the envelope on the surface of the virus is also called the capsule, which is mainly composed of lipids, which is reminiscent of the lipid bilayer of the human cell membrane and the similar compatibility principle of chemistry. To some extent this structure makes it easier for the virus to enter the host cell.
Finally, when entering the cell, there is an RNA with a positive single-stranded structure. As RNA, it has no double-stranded structure and has no error-correcting ability that can match DNA, so the new coronavirus is easier to mutate .
To be clear, this RNA structure provides the structural basis for RT-PCR, the “gold standard” for COVID-19 detection.
Image source: Zhanku Hailuo
Second, the process of the virus attacking the human body
After completing the structural observation of our enemy, we may wish to examine the virus surprise attack in a local battle in detail.
First of all, we need to be clear that the virus cannot survive on its own, that is, it must parasitize other host cells.
When a virus parasitizes a cell, it usually goes through four steps: adsorption and entry, uncoating, biosynthesis, assembly and exit.
1. Adsorption and cell entry: When the virus enters the adjacent position of the alveoli through the respiratory tract, the virus uses the spike protein as a key to specifically bind to the door lock of some cells, such as the ACE2 receptor, so as to cleverly By deceiving the cell, the portal is opened, and at the same time, it quickly passes through the lipid bilayer through the lipid envelope and enters the host cell.
Compared to other organs, human airway ciliated cells and alveolar epithelial cells have higher levels of ACE2 protein, which explains why the new coronavirus chooses the lungs to attack first.
2. Uncoating: After the virus enters the cell, the virus will use its own disguised coat-protein nucleocapsid to attract the cell factory pickets-lysosome to inactivate it. The step is called “unshelling”.
This is how the virus’s genetic material, RNA, is completely exposed inside the cell. Of course it won’t just stop there.
3. Synthesis: When the genetic material RNA invades the cell’s synthesis workshop – the ribosome, the virus finally begins its wanton reproduction. This step of “synthesis” focuses on reproducing the virus important accessory required, and thus again maps to our previous description of the virus structure:
o First, single-direction positive-stranded RNA directs the synthesis of a large number of virus-associated proteins, including nucleocapsid proteins.
o Second, single-direction plus-strand RNA is transcribed into minus-strand RNA by using itself as a template, thereby producing a new progeny plus-strand RNA. This process is repeated, resulting in a large amount of new RNA.
o Thirdly, after the negative-strand RNA is selectively converted into fragmented plus-strand RNA, various small proteins can be specifically synthesized.
4. Assembly and expulsion: So far, we have obtained three main accessories, and the core assembly can be completed. Some theories suggest that the lipid envelope is mainly obtained by dividing the lipid membrane components into itself when passing through the endoplasmic reticulum or cell membrane.
So far, the virus has completed a replicationThe whole process.
What will be its fate in the future? Whether it is long-term latent or waiting for an opportunity, this involves the fate of the virus. It can choose to increase passively as the cell replicates, or it can reproduce in large quantities, causing direct toxic killing and resource encroachment on cells.
The last question is for you. If you are a virus, in order to maximize the interests of your cluster, what will you choose?
Image source: Zhanku Hailuo
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