Do you know about corona viruses

COVID-19 is the novel strain of Corona virus. Before moving in detail, 1^st thing comes to our mind is 

“What is virus?”

·         Virus is a small infectious agent that replicates only inside the living cells of an organism or simply we call it as host cell

·         Virus do not fall strictly in to the category of unicellular micro-organisms as they do not possess cellular organization. Virus exist in between nonliving & living organism

·         In absence of host living cell this virus act as nonliving compound but when it get a chance to enter inside the host living cell it becomes active and grow

·         Virus is also known as living chemicals

·         They contain only one type of nucleic acid, either DNA or RNA but never both. Virus are obligate intracellular parasite

·         They lack the enzymes necessary for protein & nucleic acid synthesis & are dependent for replication on the synthetic machinery of the host cells

·         They are unaffected by antibacterial antibiotics

General Structure of virus

·        Viruses are much smaller than bacteria and it can only be seen under the electron microscope

·         The extracellular infectious virus particle is called the virion. It consist essentially of a nucleic acid (DNA or RNA) surrounded  by a protein coat, the capsid

·         The function of the capsid is to protect the nucleic acid from inactivation  by nucleases & other deleterious agents in the environment

·         Virions may be enveloped or non-enveloped. The envelope or outer covering is derived from the host cell membrane when the new virus is released by budding. Envelope is made up of lipoprotein.

What is corona virus?

·         Solar Corona appears when the total solar eclipse occurs, corona  is seen around the moon. Similarly when scientist first observed these virus under electron microscope, due to their spike structure present on the envelope of virus it appeared like a solar corona solar system hence they named this virus as corona due to their spikes.

·         Scientist found this corona virus in nasopharyngeal at the first time from the common cold case

·         They appear to be the second most common cause of the common cold, particularly in winter

·         There are many types of virus in this categories such as SARS,MERS,COVID-19.

Virus classification

Realm-   Riboviria

Phylum - Incertae sedis

Order - Nidovirales

Family- Coronaviridae

                                                          Subfamily- Orthocoronavirinae

                                                                     

  Structure of COVID-19

 

·         Corona the name only suggest the spikes which are made up of glycoprotein.Virus use this spike to bind withACE-2 receptor present in the host cell

·         As the shape of spike & receptor of the host cell are complimentary to each other, virus binds very firmly to the host cell by stronger bonding

·         These spikes are present on envelope of the virus. Other than these spikes, there is a small spikes known as hemagglutinin esterase these also binds to the secondary receptor sites of the cells

·         Envelope of corona virus is made up of bilipid layer

·         Envelope covers the capsid which is a protective layer of protein which covers genetic material of virus

Genetic material of these virus is positive sense single stranded RNA. There is 28000 to 33000 base pair present in genome of COVID-19.

Mechanism of COVID-19

·         Spikes of COVID-19 binds to ACE-2 (Angiotensin Converting Enzyme-2) receptor present in the host cells

·         ACE-2 receptor is present on the outer surface of cells in the lungs, arteries, heart, kidney & intestines.

·         The main function of ACE-2 receptor is to regulate the blood pressure

·         COVID-19 spike recognize the ACE-2 receptor and binds to it

·         After binding to host cell, virus enters in to the cell by fusion of envelop with the cell wall and releases capsid which contains virus genetic material into the cell

·         Protease enzyme present in the host cytoplasm hydrolyses the capsid and then viral genome is released into the cytoplasm

·         COVID-19 viral genome is positive sense single stranded RNA

·         Ribosomes present in the cytoplasm recognize this viral genome as mRNA & it is translated into polyprotein 1a & polyprotein 1ab

·         These protein forms transcriptase complex which converts positive sense single stranded RNA into negative sense single stranded RNA

·         Negative sense single stranded RNA undergoes two steps

·         First is the replication process which leads to the multiplication of positive sense single stranded RNA for next progeny virus &in second step again negative sense single stranded RNA undergoes discontinuous transcription to produce number of subgenomic positive sense single stranded mRNA which further translates and synthesis various viral proteins

·         When sufficient amount of viral genome and viral proteins are synthesized in the host cell, replication and translation is stopped

·         Assembly of viral genome and viral protein takes place & finally a matured new progeny of virus is ready for further infecting other healthy host cell

·         Matured new viral progeny releases and attacks other host cell. In this way virus grows & spread by attacking other healthy host cell which contains ACE-2 receptor