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Entry, or penetration, is the second step in viral replication. This step is characterized by the virus passing through the plasma membrane of the host cell. The most common way a virus gains entry to the host cell is by receptor-mediated endocytosis, which comes at no energy cost to the virus, only the host cell. Receptor-mediated endocytosis ...
How a virus enters a cell is different depending on the type of virus it is. A virus with a nonenveloped capsid enters the cell by attaching to the attachment factor located on a host cell. It then enters the cell by endocytosis or by making a hole in the membrane of the host cell and inserting its viral genome. [2]
Life-cycle of a typical virus (left to right); following infection of a cell by a single virus, hundreds of offspring are released. When a virus infects a cell, the virus forces it to make thousands more viruses. It does this by making the cell copy the virus's DNA or RNA, making viral proteins, which all assemble to form new virus particles. [37]
For the virus to reproduce and thereby establish infection, it must enter cells of the host organism and use those cells' materials. To enter the cells, proteins on the surface of the virus interact with proteins of the cell. Attachment, or adsorption, occurs between the viral particle and the host cell membrane.
To infect a host cell, the virus must first inject its own nucleic acid into the cell through the plasma membrane and (if present) the cell wall. The virus does so by either attaching to a receptor on the cell's surface or by simple mechanical force. The binding is due to electrostatic interactions and is influenced by pH and the presence of ions.
Viral populations do not grow through cell division, because they are acellular. Instead, they use the machinery and metabolism of a host cell to produce multiple copies of themselves, and they assemble in the cell. [74] When infected, the host cell is forced to rapidly produce thousands of copies of the original virus. [75]
Viruses, however, use a completely different mechanism to cause disease. Upon entry into the host, they can do one of two things. Many times, viral pathogens enter the lytic cycle; this is when the virus inserts its DNA or RNA into the host cell, replicates, and eventually causes the cell to lyse, releasing more viruses into the environment.
Virus Life Cycle (Simplified for RNA Viruses). Upon attaching to the cell surface, virus entry occurs via binding cell surface receptor and via endocytosis. The virus utilizes host proteins and other cell machinery to replicate. Once the viral genome has been replicated, the progeny virions are assembled and released out of the cell.