By: Emily Del Zotto


an infective agent that typically consists of a nucleic acid molecule in a protein coat, is too small to be seen by light microscope, and is able to multiply only within the living cells of a host.

General Characteristics of Viruses

Viruses are a cellular, non-cytoplasmic infectious agents.

They are smaller than bacteria, and this can pass through bacteriological filter.

Viruses are transmissible from disease to healthy organisms.

All viruses are obligate parasites and can only multiply within the living host cells.

Viruses contain only a single type of nucleic acid either DNA or RNA.

Viruses are host specific that they infect only a single species and definite cells of the host organisms.

Viruses are effective in very small doses. They are highly resistant to germicides and extremes of physical conditions.

  • Shape: spherical or golf ball-like, rod-shaped, tadpole-like, helical or polyhedral
  • Cell Wall: The capsid, which is the protein layer that surrounds and protects the nucleic acids
  • Movement: There are two types of virus movement: 1) Slow, local movement, in which the virus moves from one cell into neighboring cells. 2) Fast, systemic movement, in which the virus moves from an infection site to distant parts of the plant by hitching a ride on the plant's own veins.
  • How do they obtain energy? Viruses do not have their own energy, but rely upon the energy available within the living cell which the virus has infected.
  • How do viruses reproduce? Lysogenic Cycle a viral reproductive cycle in which the viral DNA is added to the host cell's DNA and is copied along with the host cell's DNA. Lytic Cycle a viral reproductive cycle in which copies of a virus are made within a host cell, which then bursts open, releasing new viruses.

How are viruses harmful and helpful?

Viruses are harmful because they can cause you to become very ill and can cause diseases. They can be helpful because they can be used to inject genetically modified genes into the genome of specific organ of the body and so may cure certain diseases.

Bacteriophage and Retroviruses

Bacteriophages or phages for short are viruses that attack bacteria but not humans. They have only one objective, their reproduction.

Retroviruses, such as HIV, whose RNA codes for DNA, which is then inserted into some part of the host's DNA. This virus comes with its own special enzyme, called reverse transcriptase, which facilitates this insertion.

Viruses that have killed many people.

  • Smallpox
  • Dengue Virus
  • Ebola
  • Marburg Virus
  • Influenza
  • HIV
Big image


Many viral infections resolve on their own without treatment. Other times, treatment of viral infections focuses on symptom relief, not fighting the virus. There are some medications that work directly on viruses. These are called antiviral medications. They work by inhibiting the production of virus particles. Some interfere with the production of viral DNA. Others prevent viruses from entering host cells. There are other ways in which these medications work. In general, antiviral medications are most effective when they are taken early on in the viral process.

What is a virus? How do viruses work?