Structure of coronavirus
Channel: Covid-19
Date: 13/05/2020

Viruses can only survive within a host cell so that applied to coronavirus as well. Viruses have a genetic material which enables them to reproduce however they do not have enzymes required for protein as well as nucleic acid synthesis so they need help of some other cells so that they use their machinery and produce proteins and enzymes necessary for their protection as well as for their multiplication. 

Structures of virus

All viruses have a genome which is surrounded by a protein coat known as capsid.  The protein coat i.e the capsid is basically proteins which are arranged in a symmetrical manner and form a protective shell for the nucleic acid. The symmetry may be either icosahedral i.e has 20 triangular faces or helical. So all viruses have a genome and a protein coat . Some viruses may be enveloped while some may not be enveloped (naked viruses). The envelope is made up of lipoproteins i.e lipids and proteins. The lipids are derived from the host cell membrane which the viruses infect and they acquire it while they are leaving the cell while the proteins are synthesised by the viral genome using the host machinery.

Viruses have been broadly classified into 6 types based on their genome

1. 1st class includes viruses with double stranded DNA, 
2. 2nd class, viruses with single stranded DNA, 
3. 3rd class : viruses with ds RNA viruses 
in 4th , 5th and 6th class are ss RNA viruses with some differences.
4. 4th class, viruses with positive strand ss RNA i.e RNA same as that of mRNA which can be directly translated into proteins 
5. 5th class, ss RNA viruses with RNA of opposite polarity to that of mRNA are present i.e negative starnad RNA
6.In 6th class ss RNA viruses are there but these viruses have the capability to synthesise DNA from their RNA since they possess an enzyme reverse transcriptase. 

Structure of coronaviruses

Coronaviruses belong 4th class…i.e they have singly stranded positive sense RNA with a protein coat. Coronavirus genome is very large infact it is among the largest mature RNA virus molecules known and second the nucleocapsid has helical symmetry.  Also, the coronaviruses are enveloped virus i.e apart from the protein coat they also have a lipoprotein envelope. 

The lipoprotein envelope has lipids derived from the host cell membrane and the proteins in this envelope are synthesised from the viral genome. One of these proteins known as spike protein  kind of forms a rim around the membrane. This rim gives it an appearnace similar to corona of the sun  and thats why this virus is name as coronavirus. This spike protein is the one through which virus attaches to a receptor, and then the virus and host cell membrane fuse causing entry of viral genome into the cell. 

There are 2 other proteins.. one is known as membrane protein M protein which gives the virus envelope its shape while the other is E-protein i.e envelope protein… They are said to have roles in the assembly of the virus genome , capsid and the envelope as the virus leaves the host cell.