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Prior to entry, a virus must attach to a host cell. Attachment is achieved when specific proteins on the viral capsid or viral envelope bind to specific proteins called receptor proteins on the cell membrane of the target cell. A virus must now enter the cell, which is covered by a phospholipid bilayer, a cell's natural barrier to the outside ...
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 ...
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. A hole forms in the cell membrane, then the virus particle or its genetic contents are released into the host cell, where replication of the viral genome may commence.
In some cases, the virus with an envelope will form an endosome within the host cell. [10] There are three main types of viral glycoproteins: Envelope proteins, membrane proteins, and spike proteins (E, M, and S). [11] The viral envelope then fuses with the host's membrane, allowing the capsid and viral genome to enter and infect the host.
A virus with this "viral envelope" uses it—along with specific receptors—to enter a new host cell. Viruses vary in shape from the simple helical and icosahedral to more complex structures. Viruses range in size from 20 to 300 nanometres ; it would take 33,000 to 500,000 of them, side by side, to stretch to 1 centimetre (0.4 in).
If a host cell expresses the complementary surface receptor for the virus, then the virus can attach and enter the cell. If a cell does not express these receptors, then the virus cannot normally infect it. Therefore, if the virus cannot bind to the cell, it does not display tropism for that host. Bacteria infect hosts differently than viruses ...
Parvovirus virions are small compared to most viruses, at 23–28 nanometers in diameter, and contain the genome enclosed in an icosahedral capsid that has a rugged surface. Parvoviruses enter a host cell by endocytosis, travelling to the nucleus where they wait until the cell enters its replication stage. At that point, the genome is uncoated ...
Honey bee infected with deformed wing virus. Arthropods is the largest group of animals and has shown to be a major reservoir of different viruses, both insect-specific viruses (ISV) and viruses that can infect both vertebrates and invertebrates, more known as arthropod-borne viruses (arboviruses).