Fig. 2.

Entry mechanism and life cycle of SARS-CoV-2 in host cells. The glycoprotein spikes of the virus bind to its receptor human angiotensin converting enzyme (ACE2), through receptor-binding domain (RBD), proteolytically activated by human proteases, and enters the cell through endosomal pathway. This is followed by uncovering of viral RNA in the cytoplasm and translation of ORF1a and ORF1ab to produce pp1a and pp1ab polyproteins. These proteins are cleaved by RTC proteases, which facilitate the production of full length (−) RNA copies and serve as templates for full length (+) RNA genomes. A set of sub-genomic RNAs (sgRNAs) is produced via fragmented transcription, having numerous open reading frames (ORFs), where only the closest (5′ end) is translated. The nucleocaspids are mustered in the cytoplasm, after the production of viral structural proteins. This is followed by budding in the lumen of intermediate compartment of endoplasmic reticulum (ER) and golgi apparatus (ERGIC). This is followed by exocytosis mediated release of virion from the infected cell.