Features of Host Cells: Cellular and Molecular Biology Review

As obligate intracellular parasites, viruses are completely dependent upon a host cell for their replication. They use energy generated by the host cell, and they exploit the host's machinery to manufacture viral proteins. Many of the cell's organelles, as well as the plasma membrane, are involved in viral replication processes. The organelles involved in protein synthesis, processing, and transport—namely the ribosome, rough endoplasmic reticulum, and Golgi complex—are utilized in the manufacture of viral proteins, as well, and viruses use ATP generated by the host cell's mitochondria. The plasma membrane, made of a phospholipid bilayer, is the cell's primary zone of contact with the extracellular world. As such, it is the first obstacle that a virus must overcome for entry into a cell. The Central Dogma of Molecular Biology states that DNA is replicated to create more DNA, DNA is transcribed into mRNA, and mRNA is translated by ribosomes to create proteins. All viruses are dependent upon the host's translation machinery, and many viruses will use other portions of the cell's replication and transcription mechanisms. DNA polymerase is the major enzyme involved in DNA replication, while RNA polymerase creates messenger RNA. Host ribosomes translate the messenger RNA into proteins, composed of amino acids. Viruses also have many unique strategies to ensure the translation of their proteins over host proteins.