Presentation on theme: "SB3d. Compare and contrast viruses with living organisms."— Presentation transcript:
1 SB3d. Compare and contrast viruses with living organisms. Chapter 20: VirusesSB3d. Compare and contrast viruses with living organisms.
2 Is a virus alive?Viruses are not considered living because they are missing key characteristics of living organisms.Need a host cell to reproduceDoes not maintain homeostasisDoes not carry out metabolic activitiesDoes not have organelles or cytoplasm
3 Temperate- have to incubate 2 Categories of VirusesVirulent- fast actingEx. Stomach flu-Go through the lytic cycleTemperate- have to incubateEx. Chickenpox-Go through the lysogenic cycle before entering the lytic cycle
4 Viral Structure Nucleic Acid Capsid or Protein coat Either DNA or RNA (not both)Capsid or Protein coatDNA or RNA is contained in a capsid which is composed of proteinSome viruses have an envelopea lipid membrane that surrounds the entire virus particleMany serious viruses have an envelopeSome viruses have tail fibersThese fibers act as syringes to inject viral DNA into its bacterial hostThese viruses are often called bacteriophages.
5 Viral Structure cont. Examples: Influenza is an enveloped virus
6 Shapes of Viruses Icosahedral is a geometric shape with twenty triangular flat sides.Ex. Polio virus, a type of picornavirus
7 Virus Shapes cont. Helical Shaped like a cork screw Ex. Tobacco Mosaic Virus (TMV)
8 Virus classification Based on three categories Enveloped or not DNA or RNAHelical or Icosahedral
9 Viral Reproduction Differs based on genetic material All viral reproduction takes place inside the hosts cell (obligate intracellular parasite)DNA viruses use their DNA to make RNA which directs the production of new virusesSome DNA viruses combine their DNA with the hosts DNA to direct new virus synthesisExample of DNA virus:Herpes, the disease that causes chickenpox
10 Viral Reproduction cont. RNA viruses use their RNA to direct the host cells ribosomes to make proteins that make new virusesEX. Rabies, a type of rhabdovirusRetroviruses are RNA virusesThey replicate by using an enzyme called reverse transcriptaseReverse transcriptase uses the viral RNA to make a DNA template to make a new virus (mutates rapidly)
11 Retroviruses Type of RNA virus Retroviruses are RNA viruses They replicate by using an enzyme called reverse transcriptaseReverse transcriptase uses the viral RNA as a template to make viral DNAThe viral DNA is integrated into the host DNA to make new virusesEx. HIV
12 Bacteriophages Viruses that infect bacteria They have been a significant tool in studying viral reproduction
15 Treatment of viral disease Viruses are difficult to treat because they are not living organismsViruses are unaffected by antibioticsThey lack all of the physical features that antibiotics act onVaccines and antiretroviral drugs are the only treatmentsAntiretroviral drugs do not kill the virus, they interfere with its reproductionEx. AZT is used for HIV
16 Viroids Not viruses Composed only of one loop of RNA Cause disease in plantsEx. Orange blight, potato blight, etc.
17 Prions Prions are not viruses Prions are simply malformed proteins that clump on to neurons and disrupt their functionEx. Mad Cow disease (BSE)Ex. Creutzfeld-Jacob disease (CJ disease)All prion diseases cause neural degeneration