The cell in which a virus replicates in Before a virus can replicate it must enter a host cell Before it can enter a host cell it must first recognize and attach to a receptor site on the plasma membrane of the host cell.
Most viruses are highly specific to the cells they infect. Ex: Plant viruses only infect plants Bacteriophages are viruses that infect bacteria Ex: bacteriophage T4 Viruses have two ways of infecting the host cell: -Lytic Infection -Lysogenic Infection
Viruses cause human diseases such as polio, measles, influenza, and AIDS. Viruses attack and destroy certain cells in the body → causing symptoms of the disease The best way to prevent against viral diseases is to prevent infection through vaccination.
Viruses that contain RNA as their genetic material When retroviruses infect a cell they produce a DNA copy of their RNA. Called retroviruses because their genetic information is copied backwards From RNA to DNA instead of DNA to RNA Retroviruses are responsible for some types of cancer and HIV
Lytic Cycle virus injects its nucleic acid into the host takes over the host cells metabolism causes host cell to start replicating the viruses proteins and nucleic acids virus secretes enzymes that “lyse” the host cell’s cell wall and releases new virus particles these particles can attack other host cells Lytic Infection causes host cell to be “lysed” and destroyed.
Lysogenic cycle Lysogenic virus injects its nucleic acid into a host cell Viral DNA is integrated into the host cell’s chromosome → called a prophage Every time host cell reproduces, the provirus is replicated along with it → every cell that originates from the infected host cell has a copy of the provirus
Retroviruses can cause some cancers Retroviruses that convert, or transform, normal cells → tumor viruses These viruses carry genes that disrupt the normal controls over cell growth and division
The lysogenic cycle can take place for many years At any time the provirus can be activated and enter a lytic cycle ↓ host cell is killed
A lytic infection occurs when a a. Virus infects a bacterium and kills it immediately b. Virus embeds its genome into the DNA of the host cell c. Virus enters a cell, makes copies of itself, and causes the cell to burst d. Virus inserts its DNA into the DNA of the host cell and remains part of the host cell for many generations
A preparation of a weakened or killed virus or viral protein When injected into the body, it stimulates the immune system in an effort to create permanent immunity to the disease For vaccines to be most effective it must be used before an infection begins.
Vaccines are used for the prevention of viral infections Vaccines are NOT used for bacterial infections
DiseaseSymptomIncubation MeaslesRash, fever9-11 days ShinglesPain, itching on skinYears WartsBumpy areas on skinMonths Coryza (cold)Sneezing, runny nose, fever 2-4 days HIVFatigue, weight loss2-5 years The symptoms and incubation time of a disease can indicate how the virus acts inside its host cell. Which diseases may be caused by lytic viruses? Which diseases may be caused by lysogenic viruses?