RT Book, Section A1 Wang, Fred A1 Kieff, Elliott A2 Kasper, Dennis A2 Fauci, Anthony A2 Hauser, Stephen A2 Longo, Dan A2 Jameson, J. Larry A2 Loscalzo, Joseph SR Print(0) ID 1120800759 T1 Medical Virology T2 Harrison's Principles of Internal Medicine, 19e YR 2014 FD 2014 PB McGraw-Hill Education PP New York, NY SN 9780071802154 LK accesspharmacy.mhmedical.com/content.aspx?aid=1120800759 RD 2022/05/20 AB Viruses are obligate intracellular parasites. They consist of a DNA or RNA genome surrounded by protein. They may also have an outer-membrane lipoprotein envelope. Viruses can replicate only within cells because their nucleic acid does not encode many enzymes necessary for the metabolism of proteins, carbohydrates, or lipids or for the generation of high-energy phosphates. Typically, viral nucleic acids encode messenger RNA (mRNA) and proteins necessary for replicating, packaging, and releasing progeny virus from infected cells.