Presentation on theme: "Donna Howell Medical Microbiology Gaffney High School"— Presentation transcript:
1Donna Howell Medical Microbiology Gaffney High School Coming soon to a body near you -He He He!The Viruses Unit 3Donna HowellMedical MicrobiologyGaffney High School
2HistoryIn 1892, Dmitri Iwanowski studied the tobacco mosaic virus. He found out that this unknown agent could pass through a filter, unlike bacteria.In 1930’s, Wendell Stanley found out that this unknown agent could crystallize, which means it is a chemical.In 1933, electron microscope was invented, and could see viruses by 1941.
3What is a Virus?Any of various simple submicroscopic parasites of plants, animals, and bacteria that often cause disease and that consist essentially of a core of RNA or DNA surrounded by a protein coat. Unable to replicate without a host cell, viruses are typically not considered living organisms.
4How Are Viruses Classified? DNA or RNA – that is the question!Viruses are classifed according to what type of nucleic acid core they contain: either RNA or DNA.
5Further Classification Viruses can be further classified based on what part of the body is affected:CategoryTissue AffectedExample DiseasesDermotropicSkin and subcutaneous tissueChicken pox, shingles, measles, mumps, smallpox, rubella, herpes simplexNeurotropicBrain and central nervous system tissueRabies, West Nile virus, polioViscerotropicInternal organsYellow fever, AIDS, Hepatitis A and B, Mono, Dengue feverPneumotropicLungs and other respiratory structuresInfluenza, common cold
6Size Of VirusesViruses are among the smallest known infectious particles. They come in many sizes:
7Did You Know?There is a connection between herpes and psychosis due to inflammation of the brain!
8Shapes Of VirusesViruses also come in many different shapes:
9Components Of Viruses Capsid – the outer protein coat Capsomere – protein units that make up the capsidGenome – DNA or RNAEnvelope – an enclosing structure similar to cell membraneSpikes – projections on outside of virus that allow it to attach to host cell
10Viral ReplicationViruses can replicate (reproduce) in one of two ways:Lytic cycle – this is where the virus replicates in the host cell, and causes host cell to “lyse”, or burst to release new virusesLysogenic cycle – this is where the virus incorporates its DNA into the host DNA as a prophage, and replicates as host DNA replicates.
11Lytic Cycle There are 6 stages of this cycle: Attachment – virus attaches to hostPenetration – virus enters hostUncoating – capsid removed, nucleic acid releasedSynthesis – parts for new viruses synthesizedAssembly – parts are assembledRelease – host cell lyses, new viruses releasedEx: Flu virus
12Lysogenic CycleThis is when the virus enters the host cell, but does not replicate immediately. Instead, it incorporates its genes into the host’s genes, and then one day will complete the lytic cycle. Ex: AIDS
13Viral IdentificationIn many cases, when a virus infect a cell, it causes cell death or at least cell damage. The specific imprint that the virus leaves is called the cytopathic effect (CPE). By observing the effects under the microscope, scientists can sometimes identify the type of viral infection. Many viruses have a characteristic CPE.
14How Are Viruses Cultured? Touch my egg you die, buster!Viruses can be cultured in one of 3 ways:Inside a live animalInside a fertilized chicken eggIn a viral cell culture, which is a thin layer of cells in a petri dish with special nutrients
15Did You Know?Shake ya tailfeathers!There is a link between in-utero exposure to flu and schizophrenia later in life!
16Defenses Against Viruses Go body go!What are some defenses against viruses?Body can produce antibodies, which attack and kill viruses.Some drugs can be used, such as interferon or AZTCan have a vaccine against a virus
17Types of Vaccines I got your vaccine, baby! There are 3 types of vaccines that we use for viruses:Inactivated vaccine – those made from real inactivated virus. The genome is destroyed, but the capsid remains.Attenuated vaccine – those made from “live” viruses, but in such a low dose that it does not usually cause disease.Genetically-engineered vaccine – viral proteins are produced by yeast cells, so NO actual viruses used. Safest!
18ViroidsCome on viroids!An ultramicroscopic, single-stranded molecule of RNA without a protein coat.Mostly infect plantsCause stunted growth and abnormal development.
19PrionsI’m a mad cow – get it?Proteinaceous infectious particle (single piece of protein with no capsid)Can survive heat, radiation, and chemicals that normally inactivate viruses.Causes kuru and mad cow disease.
20Get it – horoscope, cancer, crab???? Viruses and CancerGet it – horoscope, cancer, crab????It is well known that certain viruses have cancer-causing abilities. Here are a few:HPV virus – cervical cancerHepatitis B virus – liver cancerHTLV virus – leukemiaEpstein-Barr virus – Burkitt’s lymphoma