What is a Virus? n Viruses are strands of DNA or RNA inside a protective coat. n They cannot live on their own, but invade cells in your body and use them as factories to make more viruses.

What is a Virus? n This eventually kills the cell. n Diseases caused by the viruses includes colds, flu and AIDS.

Properties of Viruses n Viruses continue to mystify scientists. n They are so small and simple, that they do not fit the living cell classification. n They range in size from 0.01µm to 0.3 µm in diameter. n Viruses have been found to produce diseases or genetic changes in animals, plants, algae, fungi, protozoa and bacterial cells.

Properties of Viruses continued n Viruses have 5 properties that separate them from living cells: n 1. They have DNA or RNA - never both. n 2. Replication is controlled by the viral DNA in the host cell. n 3. They do not divide by binary fission or mitosis. n 4. Not capable of producing their own energy because they lack the required genes.

Properties of Viruses continued n 5. They depend upon the ribosomes and nutrients of infected cells for protein production.

Viral Structure Protective coat of fats and polysaccharides Protein Coat DNA or RNA not both

Invasion of the Host Cell n This is a cyclic process. n 1. Virus contacts host cell. n 2. Virus or DNA enters host cell. n 3. Host cell DNA is broken up and new viral DNA or RNA is produced. n 4. Viruses use protein from host cell membranes to make new protein coats.

Invasion of the Host Cell con’t. n 5. Viral enzymes are produced that lyse the host cells. n 6. Host cell membrane breaks. n 7. New viruses are released.

Bacteriophages n These are viruses that invade bacterial cells. n Infective cycle is the same as previous description. n In some cases the viral and bacterial cell DNA join to form a complex. n The subsequent daughter cells will contain both DNA types.

Bacteriophage Animation