Covid Flashcards
Entry of SARS-CoV-2
ss (+) RNA
Attachment: SARS-CoV-2 attaches to host cells by binding its spike (S) protein to the ACE2 receptor on the surface of human cells, primarily in the respiratory tract.
Protease Activation: The S protein is then cleaved by host proteases such as TMPRSS2, which facilitates the fusion of the viral envelope with the host cell membrane.
Endocytosis: In some cases, the virus can also enter through endocytosis, followed by fusion within endosomes.
Lifecycle of SARS-CoV-2
Entry: The virus binds to the ACE2 receptor and enters the host cell through membrane fusion or endocytosis.
Uncoating: The viral RNA is released into the cytoplasm.
Translation: The positive-sense RNA genome acts as mRNA, and the host ribosomes translate the viral polyproteins.
Replication: The viral RNA-dependent RNA polymerase (RdRp) synthesizes a complementary negative-sense RNA strand, which serves as a template for producing new positive-sense RNA genomes.
Assembly: New viral genomes and structural proteins are assembled into virions in the endoplasmic reticulum-Golgi intermediate compartment (ERGIC).
Release: The newly formed virions are transported to the cell membrane and released by exocytosis.
Why Are RNA Viruses Prone to Mutation?
Lack of Proofreading: Unlike DNA polymerases, RNA-dependent RNA polymerases lack proofreading ability, resulting in higher error rates during replication.
Rapid Replication: The high replication rate of RNA viruses increases the opportunity for mutations to occur.
Genomic Plasticity: RNA viruses often have single-stranded genomes, which are more prone to mutations than double-stranded DNA.
Impact of Mutations
Antigenic Drift: Small, gradual mutations in viral proteins, particularly in the spike protein, can reduce the effectiveness of neutralizing antibodies, affecting vaccine efficacy.
Escape from Immune Response: Mutations can lead to immune evasion, allowing the virus to persist in the host population.
Increased Transmissibility: Some mutations may enhance the virus’s ability to bind to host receptors, increasing transmissibility
Pathogenicity: Changes in the viral genome can potentially increase or decrease the severity of the disease.
