AP BIOLOGY

Detailed explanation-1: -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 world.

Detailed explanation-2: -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-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: -Without a host cell, viruses cannot carry out their life-sustaining functions or reproduce. They cannot synthesize proteins, because they lack ribosomes and must use the ribosomes of their host cells to translate viral messenger RNA into viral proteins.

Detailed explanation-5: -However, all virus particles have a protein coat that surrounds and protects a nucleic acid genome. This protein coat is called a capsid, and the instructions for making the protein subunits of the capsid are encoded in the nucleic acid genome of the virus.