NEET BIOLOGY

Detailed explanation-1: -Viruses initially stick to cell membranes through interactions unrelated to fusion proteins. The virus surfs along the fluid surface of the cell and eventually the viral fusion proteins bind to receptor molecules on the cell membrane (4). If only binding occurred, the two membranes would remain distinct.

Detailed explanation-2: -Key Points. Virus entry into animal cells is initiated by attachment to receptors and is followed by important conformational changes of viral proteins, penetration through (non-enveloped viruses) or fusion with (enveloped viruses) cellular membranes.

Detailed explanation-3: -The particular cell membrane through which viral budding occurs is characteristic for each virus. Many viruses bud through the plasma membrane, but bunyaviruses bud through the Golgi apparatus, coronaviruses chiefly through the endoplasmic reticulum, and herpesviruses through the nuclear membrane.

Detailed explanation-4: -Enveloped viruses require membrane fusion to enter a cell. They expose on their surface many copies of a fusion protein, held in a “prefusion conformation” by constraints that come either from another part of the same protein or from a different viral protein.