5 Viruses have different shapes and sizes. The arrangement of the proteins in the capsid of a virus determines the virus’s shape
6 Host Cell The cell in which a virus replicates Before a virus can replicate it must enter a host cellBefore it can enter a host cell it must first recognize and attach to a receptor site on the plasma membrane of the host cell.
7 Viral InfectionMost viruses are highly specific to the cells they infect.Ex: Plant viruses only infect plantsBacteriophages are viruses that infect bacteriaEx: bacteriophage T4Viruses have two ways of infecting the host cell:-Lytic Infection-Lysogenic Infection
9 Lytic Infection Lytic Cycle virus injects its nucleic acid into the hosttakes over the host cells metabolismcauses host cell to start replicating the viruses proteins and nucleic acidsvirus secretes enzymes that “lyse” the host cell’s cell wall and releases new virus particlesthese particles can attack other host cellsLytic Infection causes host cell to be “lysed” and destroyed.
11 Lysogenic Infection Lysogenic cycle Lysogenic virus injects its nucleic acid into a host cellViral DNA is integrated into the host cell’s chromosome→ provirusEvery 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
15 Viruses and DiseasesViruses cause human diseases such as polio, measles , influenza, and AIDS.Viruses attack and destroy certain cells in the body → causing symptoms of the diseaseThe best way to prevent against viral diseases is to prevent infection through vaccination.
17 What is a vaccine?A preparation of a weakened or killed virus or viral proteinWhen injected into the body, it stimulates the immune system in an effort to create permanent immunity to the diseaseFor vaccines to be most effective it must be used before an infection begins.
18 Vaccines are used for the prevention of viral infections Vaccines are NOT used for bacterial infections
19 The symptoms and incubation time of a disease can indicate how the virus acts inside its host cell. MeaslesRash, fever9-11 daysShinglesPain, itching on skinYearsWartsBumpy areas on skinMonthsCoryza (cold)Sneezing, runny nose, fever2-4 daysHIVFatigue, weight loss2-5 yearsWhich diseases may be caused by lytic viruses?Which diseases may be caused by lysogenic viruses?
20 Retroviruses 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 backwardsFrom RNA to DNA instead of DNA to RNARetroviruses are responsible for some types of cancer and HIV
21 Retroviruses and cancer Retroviruses can cause some cancersRetroviruses that convert, or transform, normal cells → tumor virusesThese viruses carry genes that disrupt the normal controls over cell growth and division
27 Tobacco Mosaic Virus Was the first virus to be identified Causes disease in tobacco plants
28 Knowledge checkWhat characteristic do viruses share with all living organisms?RespirationMetabolismReplicationMovement
29 Knowledge check A lytic infection occurs when a Virus infects a bacterium and kills it immediatelyVirus embeds its genome into the DNA of the host cellVirus enters a cell, makes copies of itself, and causes the cell to burstVirus inserts its DNA into the DNA of the host cell and remains part of the host cell for many generations
30 Knowledge CheckOne group of viruses that contain RNA as their genetic information areOncogenetic virusesRetrovirusesCapsidsProphages
31 Knowledge CheckFill in the blanks The nucleic acid core of a virus contains ________ or __________ All viruses contain a coat of ________ and a core of _________