Animal viruses can enter host cells through two primary mechanisms: membrane fusion and endocytosis. Understanding these processes is crucial for grasping how viral infections occur.
Enveloped viruses, which possess an outer lipid envelope, can utilize both methods for entry. In the case of membrane fusion, the virus's lipid envelope merges with the host cell's cytoplasmic membrane. This fusion allows the virus to enter the cell while leaving its envelope embedded in the host membrane. This process is unique to enveloped viruses due to their lipid layer, which facilitates the fusion with the host cell.
The second method, endocytosis, specifically receptor-mediated endocytosis, is also available to enveloped viruses. In this process, the virus binds to specific receptors on the host cell's surface, triggering the invagination of the membrane and the formation of an endocytic vesicle that engulfs the virus. Non-enveloped viruses, lacking a lipid envelope, can only enter host cells through this endocytosis mechanism, as they cannot fuse with the membrane.
In summary, enveloped viruses can enter host cells via either membrane fusion or endocytosis, while non-enveloped viruses rely solely on endocytosis. Understanding these entry mechanisms is essential for developing strategies to combat viral infections and for further studies on viral pathogenesis.