Chapter 25. 바이러스 (The Viruses)

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1 Chapter 25 바이러스 (The Viruses)

2 Generalized Structure of Viruses 2 2

3 Virus Classification Classification based on numerous characteristics Nucleic acid type Presence or absence of envelope Capsid symmetry Dimensions of virion and capsid 3 목 (order), 73 과 (family), 9 아과 (subfamily), 287 속 (genera), 2000 종 (species) 3

4 생물학의중심명제 (Central dogma) 복제 전사 번역 4 4

5 Alternative Classification Scheme David Baltimore Focuses on viral genome replication and process used to synthesize viral mrna 7 life cycle groups 5

6 볼티모어시스템바이러스분류 dsdna virus ssdna virus dsrna virus ss (+)RNA virus ss ( )RNA virus ssrna retro virus Gapped dsdna virus 6

7 Viruses with dsdna Genomes (Group I) Largest group of known viruses Most bacteriophages, archael viruses, herpes viruses, nucleo cytoplasmic large DNA viruses Some dsdna viruses rely on host s DNA and RNA polymerases 7

8 Bacteriophage T4 Some of bacteriophage enzymes synthesize hydroxymethyl cytosine (HMC), a modified nucleotide that replaces cytosine in T4 DNA HMC is then chemically modified by glucosylation Protects T4 phage DNA from E. coli restriction enzymes ( 제한효소 ) Restriction is a bacterial defense mechanism used against bacteriophage infection 8

9 Bacteriophage T4 DNA Is Terminally Redundant Telomere problem Base sequence repeated at both ends 상동재조합 (homologous recombination) Allows for formation of concatamers ( 연쇄체 ) Long strands of DNA consisting of several units linked together Structure allows for cleaving of genome for viral progeny packaging 9

10 Alpha ( ) Herpesviruses Herpes simplex virus type I (HSV 1, 입술포진 ) Herpes simplex virus type II (HSV 2, 생식기포진 ) Varicella zoster virus (VZV) chicken pox ( 수두 ), shingles ( 대상포진 ) Beta ( ) Cytomegalovirus (CMV, 거대세포바이러스 ) Gamma ( ) Epstein Barr virus (EBV) infectious mononucleosis ( 감염성단핵구증 ) 10

11 Herpesvirus Virons Icosahedral( 정이십면체 ), nm, pleomorphic ( 다형성 ), enveloped, surface spikes Envelop surrounds tegument (layer of proteins, 표피단백질층 ) which surrounds nucleocapsid Linear genomes, genes Target cells are epithelial or nerves 11

12 Herpesvirus Infections Productive (primary) infections ( 증식성감염 ) 50, ,000 virons produced/cell Cell dies due to degraded host DNA Latent infections ( 잠복성감염 ) Occurs in neuronal cells Infectious virus not detected Can be reactivated in neurons Productive infection recurs 12

13 Herpesvirus Life Cycle Circularization of genome and transcription of immediate early genes ( 전 전기유전자 ) Immediate early proteins stimulate transcription of early genes ( 전기유전자 ) Early proteins function in DNA replication, yielding concatemeric DNA. Late genes ( 후기유전자 ) are transcribed Late proteins participate in virion assembly 13

14 Herpesvirus Life Cycle DNA replication concatemer formation 14

15 Herpesvirus Life Cycle 15

16 Nucleo Cytoplasmic Large DNA (NCLD) Viruses 핵세포질성대형 DNA 바이러스 NCLD group thought to have arisen from common ancestor Similar life cycle, most in cytoplasm Enveloped, icosahedral capsids( 정이십면체 ) Virion and DNA are large Poxviridae Variola virus (Small pox virus, 천연두 ) Vaccinia virus 16

17 Viruses with Single Stranded DNA Genomes (Group II) Bacteriophages φx174 and fd Parvoviruses

18 Rolling Circle Mechanism of Replication ( 회전환복제 ) Nicking enzyme Lagging strand synthesis 18 18

19 Viruses with Double Stranded RNA Genomes (Group III) Bacteriophage 6 and rotavirus ( 설사, 탈수, 사망 ) RNA genomes cannot rely on host cell enzymes for genome replication or mrna synthesis Use RNA dependent RNA polymerase

20 Virus with Plus Strand RNA Genomes (Group IV) Bacteriophages MS2 and Qβ, poliovirus, hepatitis C virus (HCV), and tobacco mosaic virus Non segmented plus strand RNA genomes (=mrna) Replicate in cytoplasm and synthesize RNA dependent RNA polymerase Replication complex for replication & assembly

21 Poliovirus 소아마비바이러스 Attaches to human PV receptor Viral genome acts as mrna Virus uses internal ribosome entry site (IRES, 내부리보솜결합부위 ) instead of 5 cap Polyprotein translated, cleaves itself into smaller proteins Genomic RNA synthesized Assembly and lysis 21

22 Cap dependent translation Riboso me mg mrna AAAAA 22

23 Internal ribosome entry site (IRES) No 5 cap found on eukaryotic mrnas important in ribosome binding Translate its capless RNA using a 5 region on the RNA called internal ribosome entry site (IRES) Cap independent translation Numerous elements and extensive secondary structures Important for recognition of the RNA by the ribosome 23

24 Cleavage of Poliovirus Polyprotein The polyprotein has a protease activity and cleaves itself into three smaller proteins 24

25 Viruses with Minus Strand RNA Genomes (Group V) Enveloped virions, pleomorphic shape Cannot serve as mrna Must bring a RNA dependent RNA polymerase Segmented or nonsegmented genomes Rabies ( 광견병 ), Ebola, measles ( 홍역 ),hantaviruses, and influenza virus 25

26 Influenza Virus NA HA Causative agent of the flu ( 독감 ) Transmitted by inhalation or ingestion Three types of viruses A, B, C Seven to eight segments of linear RNA Hemagglutin (HA) binds host receptors Neuraminidase (NA) hydrolyzes mucus ( 점액질 ), cleaves virus from host receptor 26

AP Biology. Viral diseases Polio. Chapter 18. Smallpox. Influenza: 1918 epidemic. Emerging viruses. A sense of size

AP Biology. Viral diseases Polio. Chapter 18. Smallpox. Influenza: 1918 epidemic. Emerging viruses. A sense of size Hepatitis Viral diseases Polio Chapter 18. Measles Viral Genetics Influenza: 1918 epidemic 30-40 million deaths world-wide Chicken pox Smallpox Eradicated in 1976 vaccinations ceased in 1980 at risk population?