Fig. 2.

Life cycle of virus in an infected cell: After inhalation, virus reaches the respiratory system and internalization of SARS-CoV-2 virus starts with attachment of viral S (spike) protein on ACE2 receptor of humans, followed by TMPRSS2 mediated cleavage of S protein, which lead to internalization of virus. Viral uncoating in cytoplasm releases Ss positive sense genomic RNA (gRNA). The first step is translation of gRNA (+ve strand) into two polypeptides- pp1a and pp1ab, which is cleaved to many non-structural proteins (nsp), including RNA-dependent RNA polymerase, RdRp which is involved in viral genome replication in double membrane vesicles (DMVs). The negative strand, in another round, produces positive (+ve) strand genomic RNA and becomes the genome of the descendant viral cells. The transcribed sub-genomic RNAs is translated into various structural proteins (S, E, M and N) to create the viral progeny. S, E and M proteins enter the endoplasmic reticulum (ER), and the nucleocapsid protein, which joins with the genomic RNA (+ve strand) and combine into complete viral cell in the ER-Golgi compartment, and exocytosed out of the cell.