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
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