In what kingdom do we classify a virus? None! Viruses are not considered living, so we do not classify them with living organisms.

What Is a Virus? Viruses are non-living particles –Do not have all the criteria for life DO NOT GROW, DO NOT DEVELOP, DO NOT CARRY OUT RESPIRATION Viruses do reproduce, but only with the help of a host cell. Smaller than bacteria One drop of blood can contain six billion viruses

Virus Naming  Not named in the same way as organisms. –No genus/species scientific names  Some are named after their diseases they cause. –Ex. Poliovirus causes polio  Other viruses were named for the organ or tissue they infect. –Ex. Adenovirus infects the adenoid tissue, which causes the common cold.

Virus Naming  Some viruses are given a code because there are similar viruses that infect the same host.  Seven similar-looking viruses infect E. Coli (Bacteria) –Code T1- T7 (T = Type) –Bacteriophage – A bacteria infected with a virus.

Viral Structure  Viruses has an inner core of nucleic acid –DNA or RNA, which is injected into host cells.  The nucleic acid is protected by and outer coat of protein called a capsid.  Large viruses may have an additional layer called an envelope. –Composed of lipids, carbohydrates, and proteins. Ex. HIV

Viral Structure  4 different shapes

Polyhedral Papilloma Virus Capsid Nucleic Acid

Helical Shape Nucleic Acid Capsid 376,200x

Envelop Influenzavirus A Envelope Capsid found inside.

Bacteriophage

Attachment  Must recognize and attach to a receptor site found on the plasma membrane of the host cell. –Lock and Key model, envelops and capsids  Virus’s protein interlocks with the correct molecular shape on the receptor site. –Fools the cell into thing it is something the cell needs  Bacteriophage: Tail fibers attach to host cell

Attachment  Viruses are cell specific –Only can attach to certain kinds of cells  T4 can only attach to E. coli –Cannot infect animals, plants, or other bacteria  Polio can only infect human intestinal and never cells.  Few viruses can infect many organisms –Ex. Flu virus

Viral Replication Cycle  Virus enters the host cell and takes over its metabolism.  One of two ways –Lytic Cycle –Lysogenic Cycle

Lytic Cycle  Once inside, the virus’ genes become active and will take over the host cell’s genetic material.  Viral genes force the host cell to make new viruses.  The host cell’s enzymes, raw materials and energy are used to make copies of the virus.

Lytic Cycle (2)  New viruses exit the host cell by bursting it.  The host cell is killed  Takes about 20 mins. & makes about 200 new viruses.

Lysogenic Cycle  Begins the same way as the Lytic Cycle –Does not immediately take over, cell lives  The virus’s nucleic acid becomes integrated into the host cell’s chromosome, virus is now a Provirus  Cell carries on with its own metabolic activity; Mitosis. Daughter cells will contain the Provirus.

Lysogenic to Lytic  The provirus can be inactive from a few weeks to years. –Ex. Herpes simplex I virus, cold sores  Once the provirus is activated (may be activated by stress), the Lytic cycle begins and the cell dies