 Hello and welcome to Physiology Open. I hope you are staying home and following the instructions for your as well as for others' safety. Since coronavirus is on everybody's mind right now, let us see the structure of coronavirus. The structure of microorganisms help us to understand their various properties like how they survive, how they infect and also help us to deduce methods for detecting them and for creating ways to prevent and treat the infection. Well, viruses can only survive within a host cell because they have a genetic material which enables them to reproduce. However, they do not have enzymes required for protein as well as for this 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. So, first we will discuss the structure of viruses in general and then we will see the aspects particular to coronavirus. All viruses have a genome which is surrounded by a protein coat known as capsid. The genome may be either DNA or RNA but never ever it is both. This is contrast to all other organisms which have both DNA as well as RNA. The protein coat that is 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 that is has 20 triangular faces or it may be helical. So, all viruses have a genome and a protein coat. Now, with this some viruses may be enveloped while some may not be enveloped and who have only this protein coat. These are known as naked viruses. In the enveloped viruses, the envelope is made up of lipoproteins that is lipid 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 synthesized by the viral genome using the host machinery. So, this is the basic about structure of viruses. Now, viruses have been broadly classified into six types based on their genome. First class includes viruses with double stranded DNA. Second class viruses with single stranded DNA. Double stranded RNA viruses in third class and in fourth, fifth and sixth class are single stranded RNA virus with some differences. In fourth class, single stranded RNA viruses are there but have positive strand RNA. That is RNA same as that of mRNA which can be directly translated into proteins. While in class fifth, the single stranded RNA has opposite polarity to that of mRNA. So, these RNAs need to be first converted to positive sense RNA which can then be translated to proteins. It is not direct translation. In sixth class, single stranded RNA viruses are there but these viruses have the capability to synthesize DNA from their RNA since they possess an enzyme reverse transcriptase. Well, you may ask that why do different viruses have different genome? Well, it is not much the need of the virus. The answer is more in evolution. There were different types of organisms which arose. The ones which survived remain in nature with their own ways of replication. Okay, coronaviruses belong to this group. That is, they have single stranded positive sense RNA with a protein code. Also, they have a lipoprotein envelope. So, these are enveloped single stranded positive sense RNA viruses. So, what are the features of each of the components of this coronavirus structure? If we see the genome, we have said that it is single stranded positive sense RNA virus but the genome of coronavirus is very large. In fact, it is among the largest mature RNA virus molecule known. Secondly, the nucleocapsid of the coronavirus has helical symmetry. Now, this is an exception since generally helical symmetry is present in negative stranded RNA viruses. That is in class 5th, while positive stranded RNA viruses generally have icosahedral symmetry. So, that is also one unique feature of coronavirus. Now, let's come to the lipoprotein envelope. The lipoprotein envelope has lipids derived from the host cell membrane and the proteins in this envelope are synthesized from the viral genome. One of these proteins known as spike protein has extracellular portion and thus it projects from the membrane and kind of forms a rim around the membrane. When looked under electron microscope, this rim formed by these spike protein appears like a corona of the sun and that's why this virus is named as coronavirus. This spike protein is the one through which virus attaches to a receptor and then the virus and host cell membrane fuse together causing entry of viral genome that is this RNA into the cell. For more detail on this aspect of mechanism of action of coronavirus, there will be another video. Okay, there are two other proteins. One is known as membrane protein, M protein which gives the virus envelope its shape while the other is E protein that is envelope protein. Both of these proteins are said to have roles in the assembly of the virus genome, capsic and the envelope. So, it brings all the components of the virus together as the virus leaves the host cell. So, in this video we discuss the basic structure of viruses in general and of coronavirus in particular. Okay, thanks for watching the video. If you liked it, do not forget to subscribe to the channel Physiology Open. Thank you.