1.1 Life cycle of the Coronavirus
Coronaviruses (CoVs) are zoonotic, spherical (diameters of approximately
60-140 nm), positive-sense enveloped RNA viruses, belonging to theCoronaviridae family, including four genera ofAlphacoronavirus , Betacoronavirus ,Deltacoronavirus , and Gammacoronavirus (Cascella et al.,
2020; Li et al., 2019).
The betacoronavirus genome including 2019-nCoV comprises of the
5’-untranslated region (5’-UTR), 3’-untranslated region (3’-UTR), open
reading frame (ORF) 1a/b, structural proteins and accessory proteins.
Sixteen non-structural proteins (nsp 1-16) are encoded through
proteolytic processing (3CL and PL proteases) of the replicase
polyproteins (pp1a and pp1ab) encoded by the ORF1a/b. Nsps progress the
formation of the replication‐transcription complex and indirect escape
from the host immune system (Chan et al., 2020).
The ~30,000 Nucleotide viral genome also, express four
main structural proteins of spike (S), membrane (M), envelope (E), and
nucleocapsid (N) encoded from the 3′ end of the viral genome (Figure 1).
The attachment of 2019-nCoV via the interaction of its S protein with
angiotensin converting enzyme receptor on the host cell is the primary
step in its life cycle and followed by proteolytic cleavage of S
protein, the virus enters the cytosol. The second step is the expression
of replicase proteins. Following replication and RNA synthesis (Third
step) and assembly (last step), virions are released from the cell
surface by exocytosis (Figure 2) (Fehr and Perlman, 2015).