Viruses

Part 5: The Structure and Function of Animal Viruses

More of this Feature • Viruses • Virus Replication • Bacterial Viruses • Plant Viruses and Viroids • Viruses and Cancer Join the Discussion "Is a virus a living thing?" SHELLSHELL Related Resources • Microbiology • Virus Animations • Virology • Virology Images

In the first part of this series about viruses, we looked at general virus structure and function. As is true with most organisms, structure and function are thoroughly intertwined. This week we continue the series with a look at animal viruses.

At one time or another, we have all most likely been infected with a virus. For instance, colds and the chicken pox are two common ailments that are caused by viruses. As we have seen before, animal viruses are intracellular obligate parasites that reproduce only after invading the host animal cell.

HIV Infecting Human Lymph Tissue Image copyright Dennis Kunkel.

Virus Types

There are several types of animal viruses. They are commonly grouped into families according to the type of genetic material present in the virus:

Double-Stranded DNA

Double-stranded DNA viruses usually have a polyhedral or complex structure. Examples include: Papilloma (cervical cancer and warts), Herpes (simplex I and II), Epstein-Barr virus (mononucleosis) and Variola (smallpox).

Single-Stranded DNA

Single-stranded DNA viruses usually have a polyhedral structure and depend on adenoviruses for parts of their growth.

Double-Stranded RNA

Double-stranded RNA viruses usually have a polyhedral structure with the diarrhea viruses being a common example.

Single-Stranded RNA

Single-stranded RNA viruses are usually of two subtypes: those that can serve as mRNA and those that serve as a template for mRNA. Examples include: the Rhinovirus (common cold), AIDS, Rabies and the Influenza viruses.

Vaccines

Vaccines are made from harmless variants of viruses to stimulate an immune defense against the "real" virus. While vaccines have all but eliminated some illnesses such as smallpox, they are usually preventative in nature. They can help prevent an infection, but do not work after the fact. Once a person has been infected with a virus, little if anything can be done to cure a viral infection.

Share Your Opinions

What do you think? How does the structure of an animal virus help determine its function? Would you classify a virus as living or nonliving? Come on over to the Biology Forum and share your thoughts, opinions and feelings.

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