Viruses are structurally simpler than regular cells. Outside of the host cells, viruses are inactive. However, inside living cells, viruses show some of the characteristics of living things.
Viruses are not made up of cells. Compared to animal and plant cells, viruses are structurally simple. Viruses are even simpler than bacteria cells. The basic of structure of all viruses is similar. Viruses have a core of nucleic acid surrounded by a protein coat. At their core, all viruses contain either DNA or RNA. Unlike animal and plant cells, viruses do not contain both nucleic acid.
The Capsid is the DNA or RNA core of a virus that is surrounded by a protein coat. The capsid protects the nucleic acid. Besides a Capsid, some viruses, especially animal viruses, are covered with another protective coating called an Envelope. The Envelope of some viruses are covered with spikes made of carbohydrates and proteins. The spikes enable viruses to chemically discern(identify) and attach to the cells they infect.
The shapes of viruses are determined by the arrangement of proteins in their Capsid. Some viruses are rod-shaped, such as the Tobacco Mosaic virus. Other viruses are polyhedral, such as the Adenovirus, and Polio virus.
Scientists discovered that viruses are extremely small and/or microscopic. More than 3,000 particles of Polio virus could fit end to end in a straight line across the period at the end of this sentence. Since viruses are microscopic, viruses are typically measured in nanometers (nm).
Viruses have some characteristics of living organisms. Like living organisms, viruses contain nucleic acids and proteins. Inside living cells, viruses can reproduce, but not by the process of mitosis like most living cells.
Viruses lack some characteristics of living organisms. Outside of living cells, viruses are not alive. Outside of the living cells, viruses cannot move, grow, or reproduce. Viruses require living cells called host cells to be "alive". Ultimately, viruses act as parasites and harm or destroy their host cells.
To learn more about the characteristics on Viruses visit this site : http://pc65.frontier.osrhe.edu/hs/science/bvirus.htm