Understanding the Molecular Biology of SARS-CoV-2 and the COVID-19 Pandemic: A Review

Figures & data

Table 1 Zoonotic Transmission of Coronaviruses

Virus	Origin of Pathogen	Natural Reservoir Host	Virulent Coronavirus	Cell Receptor
SARS-CoV	Palm civets, raccoon, dogs, domestic cat, and ferret badgers	Bat	SARS	ACE2^Citation69
MERS-CoV	Dromedary camels	Bat	MERS	DPP4^Citation70
SARS-CoV-2	Unknown	Unknown	COVID-19	ACE2^Citation7

Abbreviations: SARS-CoV, severe acute respiratory syndrome coronavirus; MERS-CoV, Middle East respiratory syndrome related coronavirus; COVID-19, coronavirus disease 2019; ACE2, angiotensin-converting enzyme 2; DPP4, dipeptidyl peptidase 4.

Figure 1 Schematic diagram of SARS-CoV-2: (A) SARS-CoV-2 is a positive-sense, single-stranded enveloped RNA.

Notes: The lipid envelope (E) is studded with several spike (S) glycoproteins giving the virus a crown-like appearance. The membrane (M) glycoprotein is the most abundant structural protein and spans the envelope. (B) The 5′ end of the SARS-CoV-2 genome consists of open reading frame (ORF)1a/b that encodes a polyprotein, which is post-translationally cleaved into 16 non-structural proteins (nsp1–16), including RNA-dependent RNA polymerase (RdRp). The 3′ terminus of the viral genome contains ORFs encoding the four main structural proteins, spike (S), envelope (E), membrane (M), and nucleocapsid (N), as well as nine putative accessory factors. Figure created with BioRender.com. Figure adapted from Wang N, Shang J, Jiang S, Du L. Subunit vaccines against emerging pathogenic human coronaviruses. Front Microbiol. 2020;11:298.³⁰ Creative Commons Attribution License (CC-BY 4.0; https://creativecommons.org/licenses/by/4.0/legalcode).

Table 2 Variants of SARS-CoV-2 Reported Worldwide²⁰

Variant	Country of First Case	Countries Reported in (no.) ^a	Transmissibility ^b	Virulence	Number of Mutation	Diagnostic Assay ^c	Mutation Type
B.1.1.7	United Kingdom	137	43% to 90%^Citation71	NA	18	Work	H69/V70 del,Y144 del, N501Y, A570D, P681H, S106/G107/F108 del
B.1.351	South Africa	85	NA	NA	8	Work	L242/A243/L244 del, K417N, E484K, N501Y, S106/G107/F108 del
P.1	Brazil	52	42%^Citation72	NR	21	Work	K417T, E484K, N501Y, S106/G107/F108 del

Notes: ^aBased on weekly report published on 20 April 2021 by WHO; data from reference;⁷³ bTransmissibility is relative to that of the original SARS-CoV-2 strain reported in UK, USA, Ireland, Switzerland, and Denmark; ^cDiagnostic test capable of identifying those variants.

Abbreviations: NA, not available; NR, not reported.

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