Diversity of Life I Notes Week 3
Diversity of Life I Notes Week 3 210
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This 9 page Class Notes was uploaded by Jacob Erle on Saturday September 19, 2015. The Class Notes belongs to 210 at Syracuse University taught by Dr. Justine Weber in Fall 2015. Since its upload, it has received 61 views. For similar materials see Diversity of Life I in Foreign Language at Syracuse University.
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Date Created: 09/19/15
Diversity of Life I Notes Week 3 91515 Viral Diversity De nition amp Features What is a virus Virus in Latin poisonous venomous slime Manfred Eigen Mathematician amp virologist genetic program carrying the message quotReproduce Me All viruses share the following features set of 1 genomic nucleic acid molecules DNARNA not both singe or doublestranded linear or circular positive 5 to 3 negative sense 3 to 5 or ambisense partpositive and partnegative refers to how strand of viral DNARNA gets translated nuceic acid encapsulated in a protein coat some viruses are surrounded by lipoprotein membrane with lipids proteins and carbohydrates of host origin Mediate their own replication by usurping host proteinsynthesizing ability forces protein to synthesize more viral cells transmissible and cause disease in at least 1 host submircoscopic 10400nm in any 1 direction 3 orders of magnitude smaller than bacteria amp lterable pass through 022uM lter infectious obligate diseasecausing parasites pathogens that mutate and evolve do not reproduce via binary ssion but replicate like nucleic acids 107virions viral particles occupy less than 1 of the volume of a typical eukaryotic cell come in a wide assortment of shapes sizes genomes etc very diverse no synthetic capabilities Are Viruses Alive l Depends on your de nition of life if life cellular life then NO if life set of mutating and evolving genes then YES Not Alive aceuar entities not selfreplicating no oxygen exchanges Not really a valid argument oxygen is toxic to other organisms scientists consider iving nutrition not required to survivereplicate ack nite lifespan ack complexity of biological organization have one all their own instead ack metabolism need a host cell to synthesize new virions can be created de novo from nothing from DNARNA amp protein molecule can be crystallized and remain viable in crystalline form Alive possess genes evolve by Natural Selection repicate by making multiple copies of genetic material and synthesize protein to repackage genetic material obigatory parasitic bacteria are considered alive exchange genetic info with living cells quotinventquot new genes through recombinationreassortment International Committee on Taxonomy of Viruses ICTV prior to 2000 ICTV considered them living since then not living 2005 report of ICTV dubs them quotbiological entitiesquot Who Cares if viruses are organisms they should be included in treeoflife What about Last Universal Common Ancestor LU CA symbiogenesis and evolution of nucleus and eukaryotes Viral Species Concept Biological Species population of morphologically similar fertile organisms reproductively isolated from other such groups does this apply to viruses which replicate asexually CTV believes so viruses are a set of genes that mutate and evolve But they don t consider viruses to be alive Viral Species a polythetic sharing several characteristics in members of a group but are not needed for classifying that group class of viruses that make up a replicating lineage and occupy a certain niche Who Cares vaid viral species concept has practical value for aiding in diagnosis control and treating viral diseases Poiovirusvaccines work since coat proteins are highly conserved ln uenza virusvaccines don t work coat proteins not conserved HVvaccines don t work virus is very variable heps to identify potential vectors or growth sites of unknown viral pathogens SARS Ebola 9th report of ICTV updated in 2014 describes 3187 species group GenBank has sequences showing 3142 other unofficial virus species not yet formally recognized For classi cation the folo Wing features are most important nuceic acid type presenceabsence for envelope capsid symmetry size and shape of virions viruses are conveniently grouped into groups that infect prokaryotes algae fungi inverts vertebrates even other viruses Characters used in Viral Taxonomy to differentiate orders type and organization of viral genome viral replication strategy virion structure Characters used to differentiate species genome sequence relatedness natura host range cell and tissues trophisms it prefers degree of pathogen severity how does it get transported from 1 host to another insects fungi touch physiochemica properties of virion antigenic properties of viral proteins The Baltimore System has grouped viruses into 7 different categories based genome method of replication and mRNA synthesis all these different methods means wider range of potential host organisms more options for recombination Virus quotGrowth Cyclequot all viruses have to do this Uncoating viral protein coast is removed Transcription naked viral nucleic acid acts as template for production of viral mRNA or is the mRNA itself Transation viral MRNA translated by host ribosomes and tRNAs into viral proteins Replication parent viral nucleic acid copied for future virions process catalyzed by enzyme viral replicase Assemby viral coat proteins and nucleic acids assemble to form complete virions Release progeny virions released from the cell to infect other cells and other susceptible individuals cell lysis budding plasmodesmata vectors etc 91717 Viral Diversity Cont VirusCell Interactions Cytocidal Infections cell death as end result of infection Lysis many bacterial virus infections eg T4 Inhibition of host NA or protein synthesis Picorna Adeno Herpesviruses Damage to lysosomes that release hydrolytic enzymes Alter membranes that enhance IR attack HIV Viral proteins with direct toxic effects in uenza amp mumps Viral inclusions that disrupt cell integrity Rabies Herpes Arenaviruses Chromosomal disruption Herpesviruses Cell transformed into malignancy HTLVirusesleukemia Noncytocidal Infections Acute or Persistent chroniclatent Acute infections viruses ushed out of body quickly by various defense mechanisms eg cold and u viruses Persistent infections 2 types chronic or latent Chronic infections infected cells continually produce virions HIV Hep B Latent infections infected cells don t continually produce virions virus is dormant for period of time before becoming active again during latency no virus symptoms or antibodies are detectable Herpes EBV Cytomegalo human tumor viruses Persistent infections often are lysogenic incorporate DNA into host chromosomal DNA virus integrated into DNA Provirus cell is lysogenized stress can trigger provirus to become lytic herpes Adeno Retroviruses prophage has profound effects on a cell stereptococci E coli must be lysogenized with speci c prophage to become virulent provirus is passed on to daughter cells l 2 ways to generate infected cells many putative cancer viruses are temperate lysogeny can confer advantages to the virus as well as the host Darwin s Blind Spot Darwin was insistent on gradual Change No one has any proof con rming one way or the other for changing 1 species into another Competitive struggle mechanism TH Huxley posited quotsaltationismquot rapid jumps Symbiosis many examples of cooperative partnerships that contradict the competitive struggle mechanism central to Darwinian evolution symbiosis de ned by Anton deBary in late 18005 argued symbiosis was common in biology and a major force in evolution NeoDarwinism amp Svmbiodenesis Lynne Margulis bending of Darwin and Mendel in symbiogenesis 2 life forms join genomes honed by evolution not random but a creative force Margulis suggests symbiogenesis is the only evolutionary force Svmbiodenesis and the Eukarvotic Cell SET Serial Endosymbiotic Transfer suggests eukaryotic cells formed from series of symbiotic events inside cells of speci c bacteria and archaea from which all eukaryotic life branches from see origin of mitochondria chlorplasts refuses to consider viruses as possible point of origin most biologists accept SET but little evidence to support idea with origin of nucleus Viral EukaryogenesisNuclearViriogenesis According to Margulis s theory ancient archaeon engulfed by bacterium many problems with this VE hypothesis suggests an RNA cell not DNA cells was infected by virus and adapted as an organelle likely pox or mimiviruses Virus World Concept concept of Koonin suggests viruses predate cells viruses rst evolved from precellular RNA world formed on iron sul de crystals deep in hydrothermal vents theory that viruses would transfer some of their genes to bacteria and archaea via fusion endosymbiosis viruses as source of new cellular DNA info proteins 3 Domains 3 Viruses Hypothesis Bacteria Archaea and Eucarya Proposed by Forterre 2006 LUCA was an RNA cell 3 independent transfers of DNA from viruses to RNA cells leading to formation of 3 domains Interesting Facts the size of human genome is only about 40000 genes ony 10x as many genes as a bacterium 4x as many as a fruit y amp 2x as many as a nematode worm we share 2758 of our genes with fruit ies 2031 with worms and 1523 with both lUnquestionable proof all life has a common ancestry Viruses as Force of Diversity amp Evolution retorviruses and tranposons make up half the human genome and more than 90 of genome of plants common in all other life forms too elements are viral in origin many found in the sex chromosomes staby integrated lysogenic persistent and inherited not junk DNA but thought to be important in speciation process Retroviruses Placenta amp Origin of Live Birth Endogenous retroviruses are present in all vertebrates human genome has 22 ERV families highly transcribed in embryonic andor germine tissue code for viral genes ex envelope gene for protecting virus itself that provide essential cell functions Enveope protein gene codes for quotsyncytinquot viral gene expressed in placenta drives implantation of embryo to uterine wall suppresses maternal immune response and inhibits transmission of related retroviruses Origin of Live Birth Hypothesis ERVs led to development of placenta and inhibiting materal IR lContribution to development of life ERVs may also protect host genome against any related virus colonization isolate lines of same host species Contribute toward speciation Viruses Plants and Insect Evolution retroposons are found in high amounts in most plant chromosomes today most are inactive Pant ERVs are closely related most are inactive defective or unable to generate intact virus vary in number and type based on plant family cosely related in terms of phylogenetics to fungal and insect retropossons theory of fungus involvement in evolution of early plantanimal Conclusion we see viruses mainly as pathogens but we have little to no clue of actual viral diversity possible to start looking at viruses as fundamental life forms drivers of evolution END OF NOTES