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General Biology II Lecture > viruses > Flashcards

viruses Flashcards

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1
Q

h

A
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2
Q

Nature of viruses

A
  • All viruses
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3
Q

Viruses structure

A
  • Nearly all viruses form a protein sheath, or capsid, around their nucleic core
  • composed of repeats of 1 to a few proteins
  • some viruses store specialized ensymes with nucleic acid core
  • Reverse transcriptase notr found in host
  • Many animal viruses have an evelope derived from host cell membrane with viral proteins
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4
Q

Viral shape:

A

Helical capsid

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5
Q

Viral shape:

A

Icosahedral capsid

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6
Q

viral shape

A

Icosahedral head: helical tail

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7
Q

ral shape:

A
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8
Q

Viral hosts

A
  • Viruses are olbigated intracellular parasites in every kind of organism investigated
  • host range- types if organism infected Each type of virus has limited host range
  • tissue tropism- inside a host the virus may only infected ceratin tissues
  • viruses can remain formant or latent for years
  • chicken pox can reemerge as shingles
  • more kinds of viruses exist than kinds of organism
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9
Q

Viral Replication

A
  • infecting virus can be thought of as a set of instructions
  • viral genome tricks host cell into making viruses cell with a virus is often damaged by infections
  • viruses can only reproduce inside cells
  • outside, they a re metabolically inert virions
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10
Q

Viral replicatiom #2

A
  • Viruses lack their own ribosomes and enzymes for protein and nucleic acid synthesis
  • Virus hijacks the cell’s transcription and translations machineries ti express
  • early genes
  • middle genes
  • late genes
  • end result is assembly and release of viruses
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11
Q

Viral shapes

A
  • Most viruses come in 2 simple shapes
  • helical- TMV, rodlike or theadlike
  • Icosahedral- soccer ball shape
  • ## Some viruses are compled
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12
Q

Icosahedral virion

A
  • structure
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13
Q

complex virus with binal symmetry

A
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14
Q

Viral genomes
#1

A
  • Vary greatly in both type of nucleic acid number of strands
  • most RNA viruses are single-stranded
  • replicated in the host cell’s cytoplasm
  • replication in cytosol is error- prone= high rates of mutation
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15
Q

Viral genomes #2

A
  • RNA viruses
  • positive- strands virus- ciral RNA serves as mRNA
  • Negative-strands virus- genome is complementary to the viral mRNA
  • Retroviruses (HIV) employ reverse transcriptase to reverse transvribe viral RNA into DNA
  • Most DNA viruses are double -stranded
  • replicated in nucleus of eukaryotic
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16
Q

Gigant viruses

A
  • Most viruses fit through a 500-nm filter
  • mimivirus does not; has a virion 150nm in diameter, genome
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17
Q

Bacteriophage

A
  • Viruses that infect bacteria
  • diverse and united only by bacterial host
  • called phage for shot
  • E. coli-infecting voruses are the best studied
  • included the “T” series (T1, T2, etc)
  • viruses have also been found. in archea
  • different from bacterial virusws
  • characterization in early stages
18
Q

Reproductive cycles of Bacteriophage: Lytic cycle #1

A
  • Attachment or adsorption
  • target part of bacterial outer surface
  • oenetration or injection
  • T4 pierces cell wall to inject viral genome
  • Synthesis
  • Phagen takes over the cell’s replication and protein synthesis enzymes to synthesize viral components
19
Q

Reproductive cycles of Bacteriophage: Lytic cycle #2

A
  • Assembly
  • Assembly of components
  • release
  • Mature virus particles are releaae through enzyme that lyses host or budding through host cell wall
  • Eclipse period
  • Time between adsoption and the formation of new viral particles
  • If a cell is lysed at this point, fe if any active virions can be released
20
Q

Reproductive cycles of bacteriophage: Lysogenic cycle

A
  • Latent phase; virus not immediately kill infected cell
  • Integrate virus nucleic acid into host cell genome
  • Integration allows a virus to be replicated along with the host cell’s DNA as the host divides
  • temperate or lysogenic phage
  • Integrated genome called prophage; cell containing a prophage called lysogen
21
Q

Phage A

A
  • Phage lambda of E.coli
  • Best studied lysogenic phage
  • when phage infects a cell, the early events constitute a genetic switch that will determine wheter the virus is lytic or lysogenic
  • induction during stress
  • prophage can be excised and begins lytic cycle
  • requires turning on the gene expression necessary for the lytic cycle
22
Q

Phage conversion

A
  • During integrated portion of lysogenic cycle, some viral genes many be repressed
  • phenotype or characyeristics of the lysogenic bacterium can be altered by the prophage
  • vibrio cholerae
23
Q

Human Immunodeficiency viruses

A
  • HIV causes acquired immune deficiency syndrome (aids)
  • AIDS was first reported in the U.S in 1981
  • origin in Africa in 1950s
  • closely related to simian immunodeficincy virus
  • Some people are resistant to HIV infection
  • Exposed repeatedly never become positive
  • others become HIV- positive without developing AIDS
  • ## others have little resistance and progress rapidly from infection to death
24
Q

HIV resistance

A
  • Variability resistance may be due to selective pressure by smallpox virus
  • before its eradication, smallpox killed billions
  • people resistant to HIV infection have a mutation in the CCR5 gene
  • Historical appearance and distribution of this allele correlates with timing anf geography of smallpox
25
Q

HIV infection compromises host immune system

A
  • HIV targets CD4+ cells, mainly helper T cells
  • withut these cells, the body cannot mount an effective immune response
  • host may ultimately fie from a variety of opportunictic infections
  • does not normally cause disease
  • clinical symptoms usually appear after 8-10 year latent period
  • provirus integrates in genome
26
Q

HIV testing spread of AIDS

A
  • HIV testing
  • not a test for circulating cirus
  • test for presence of antibody against HIV
  • Spread of AIDS
  • carries have no clinical symptoms but are infectious
  • infection continues throughout latent period
  • mutation allows the virus to overcome immune system and AIDS begins
27
Q

HIV infection cycle #1

A
  • Model for animal viruses
  • details may vary for other viruses
  • Attachment
  • virus attacks CD4+ cells
  • viral gp 120 attaches to CD4 protein on macrophages and CD4+ cells
  • coreceptors like CCR5 affect likehood
28
Q

HIV infection cycle #2

A
  • Replication
  • Reverse transcriptase
29
Q

Evolution of HIV

A
  • During an ifection, HIV is constantly replicating and mutating
  • eventually virus mutates to infect a broader range of cells, leading to loss of T- helper cells
  • Destruction of T cells
30
Q

AID treatments #1

A
  • ## FDA lists 34 antiretroviral drugs used in AID therapy
31
Q

Vaccine development for HIV has been unsuccessful

A
  • Problem had been seen as high mutation rate
  • Real problem is no vaccine yet has produced strong cellular immune respsonse
  • Attenuated SIV vaccine
32
Q

Influenza #1

A
  • One od the most lethal viruses in human history
  • influenza pandemic of 1918 and 1919 through to have infected 1/3 of the world’s population
  • Flu virusees are enveloped animal viruses
  • 3 “types” based on capsid protein
  • type A- serious epidemics in humans and other animals
  • Types B and C- mild human infection
  • Subtytypes differ in protein spikes
  • Hemagglutinin (H)- Aids in viral entry
  • Neuraminidase (N)- Aids in viral exit
33
Q

Influenza #2

A
  • H and N molecules accumulate mutations
  • Thus we have yearly flu shots, and not a single vaccine
  • Type A viruses are classidied into 18 distinct H subtypes and 11 distinct N subtypes
  • Flu viruses can also undergo genetic recombination when 2 subtypes infect the same cell
  • creates novel combinations of spikes unrecognizable by human antibodies
34
Q

Viral recombinations has caused pandemics

A
  • Spanish flu of 1918, A (H1N1)
  • killed 50-100 million worldwide
  • Asia flu of 1957, A (H2N2)
  • killed over 100,000 Americans
  • Hong Kong flu of 1968, A (H3N2)
  • infected 50 million in U.S., Killing 70,000
35
Q

New strains of flu

A
  • New strains of flu often originate in the Far east
  • virus host are ducks, chicken, and pigs
  • In Asia, often live in close proximity to each other and humans
  • Simultaneous infection with different strains gavirs genetic recombination
  • H1N1 pandemic of 2009- viral reassortment of avian, human, and swine viruses
  • death toll was similar to seasonsla influenza, but affected more younger people
36
Q

Emergin viruses

A
  • Viruses that originate in one organism the pass to another and cause diseases
37
Q

Ebola virus

A
  • Cause severe hemorrhagic fever
  • Among most lethal infectious diseases
  • Lethality rates >90% in outbreaks in Africa
  • Natural host in unkown
38
Q

SARS coronavirus

A
  • Seevere acute respiratory syndrome
  • pneumonia-like symptoms, fatal in 8% of cases
  • caused by coronavirus
  • mutation rate loe
39
Q

Viruses and Cancer

A
  • Viruses may contribute to about 15% of all human cancers
  • Viruses can cause cancer by altering
40
Q

Prions

A
  • “Proteinaceous infectionns particles”
  • Cause transmissible spongiform encephalopathies (TSEs)
  • “Mad cow” disease- BSE
  • Scrapie in sheep
  • Creutzfeldt- jacob disease in human (CJD)
  • Host has normal prion proteins (PrPc)
  • Misfolded proteins (PrPsc) causes normal PrP to misfold, cause disease
41
Q

Viroids

A
  • Tiny naked molecules of circular RNA
  • Causes diseases in plants
  • recent outbreak killed over 10 million coconut palms in the philipines

General Biology II Lecture (25 decks)

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