The general structure of viruses consists of nucleic acid, capsid and envelope. They contain only one of the nucleic acids (DNA or RNA) as genetic material. These can be single or double stranded. The capsid consists of multiple protein structures called capsomeres. Nucleic acid and capsid structure is called nucleocapsid together. This nucleocapsid structure may have a structure called envelope in some viruses.
Viruses can only reproduce in the living environment, so they can be identified as infectious agents that have to live inside the cell. They are metabolically ineffective outside the cell.
Viruses are structurally classified as follows.
Cubic ( Ikozahedral) structure is a type of capsid that can be enveloped or not, with an angular structure formed by the combination of 12-20 capsomers. Many human, animal and plant viruses have this nature. Tomato Yellow Mosaic virus (TYMV), Polio viruses, adeno viruses and herpes viruses are examples of this structure.
Helical structure contains capsid proteins surrounding the nucleic acid in the form of a helix. It is the most fragile virus structure. Tobacco mosaic virus is an example of this group.
Complex virus structure is a structure where icosahedral and helical virus structures coexist. Head and tail morphology occurs. This structure is unique to viruses that infect bacteria and are called bacteriophages. The head is icosahedral and the tail is helical. It is attached to the bacteria with its tail.