**2. History**

Since the discovery of the virus in China in late 2019, the SARS CoV-2 pandemic has progressed through numerous stages. Patients with pneumonia-like symptoms were reported from various local health institutions in Wuhan city of China in December 2019. The reason was unknown, and the majority of the patients came from Wuhan's sea/wet food market. The pathogen was identified and confirmed in the laboratory using real-time polymerase chain reaction, and next-generation sequencing. Because its genome did not entirely match any previously sequenced viral genome and the clinical signs were distinct from other recognized viral diseases, the virus was named 2019-nCov, where "n" stands for "novel" [5], and the disease was called COVID-19. The novel virus was classified as a Beta coronavirus based on the highly conserved protein-encoding open reading frame (ORF) 1a/1b sequence. As a result, the International Committee on Taxonomy of Viruses changed the nomenclature to SARS CoV- 2 [6].

### **3. Evolution**

Based on mutation research, Li et al. [7] proposed that the virus appears to have emerged in late summer 2019 in China, and it may have invaded the West as early as October 2019. According to Dorp CH et al. [8], the illness spread globally most likely from the start of the epidemic. By Chaw SM et al. [9], SARS-CoV-2 spread cryptically well before the late 2019 outbreak in China, and Gambaro et al. [10] suspect the same for France. It is known that the SARS CoV-2 infection started in China, however, it is assumed that the virus arose in a mine in China in 2012, was collected in a laboratory, that may have escaped during manipulations in 2018 or 2019 [11]. This explanation might account for the virus's circulation before the epidemic; during this early era, the virus could have undergone unnoticed mutations.

### **4. Structure**

Coronaviruses are members of the Coronavirinae subfamily of the Coronaviridae family, which includes four genera as mentioned earlier. CoVs have a single-stranded Positive-sense RNA genome (27–32 kb) which is bigger than any other kind of RNA virus. The capsid was formed outside the genome by the nucleocapsid protein

#### *Perspective Chapter: Tracking Trails of SARS CoV-2 – Variants to Therapy DOI: http://dx.doi.org/10.5772/intechopen.106472*

(N), and the genome is further packed by an envelope that is associated with three structural proteins: membrane protein (M), spike protein (S), and envelope protein (E) [12]. After the virus was confirmed to be the member of the coronavirus family, the genome size of SARS CoV-2 which was sequenced which approximately was found to be 29.9 kb [13]. Other than the structural proteins, SARS-CoV-2 contains 16 non-structural proteins (nsp1 to nsp16). Majorly, to mention a few, Nsp1 mediates RNA processing and replication. Nsp2 modulates the survival signaling pathway of the host cell. Nsp3 is believed to separate the translated protein. Nsp4 is a transmembrane domain 2 (TM2) protein thus promotes alterations in the endoplasmic reticulum membranes. Nsp5 participates in the polyprotein process during replication. Nsp6 is a likely transmembrane domain. The presence of Nsp7 and Nsp8 boosted the combination of Nsp12 with template-primer RNA. Nsp9 is a protein that binds to ssRNA. Nsp10 is required for viral mRNA cap methylation. Nsp12 includes the RNA-dependent RNA polymerase (RdRp), which is required for coronavirus replication/translation. Nsp13 binds ATP and the zinc-binding domain for replication and transcription. Nsp14 is an exoribonuclease proofreading domain. Endoribonuclease activity of Nsp15 is Mn (2+) dependent. Nsp16 is a 2'-Oribose methyltransferase [14, 15]. According to one study, NSP-mediated effects on splicing, translation, and protein trafficking can suppress host defenses. When infected with SARS CoV-2, NSP16 binds to the mRNA recognition domains of the U1 and U2 snRNAs, suppressing mRNA splicing. NSP1 binds to 18S ribosomal RNA in the ribosome's mRNA entry channel, interfering with mRNA translation. NSP8 and NSP9 bind to the 7SL RNA, which is found at the Signal Recognition Particle, causing protein trafficking to the cell membrane to be disrupted [16].

SARS CoV-2 virus contains a series of spike proteins on the surface. Microscopically, this virus appears like a crown, which gives rise to its name *corona,* which in Latin means crown [16, 17]. The structural and spike proteins are responsible for allowing the virus to attach to the membrane of the host cell. It contains a receptor binding domain that recognizes a specific receptor ACE-2 (Angiotensin Converting Enzyme- 2 Receptor), which is expressed in the lungs, heart, kidneys, and intestines [5, 18]. These proteins bind to the ACE-2 receptor with at least the same affinity and potentially as much as 20 times greater affinity than the SARS CoV-2 virus [6].
