viruses Flashcards
1
Q
h
A
2
Q
Nature of viruses
A
- All viruses
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
4
Q
Viral shape:
A
Helical capsid
5
Q
Viral shape:
A
Icosahedral capsid
6
Q
viral shape
A
Icosahedral head: helical tail
7
Q
ral shape:
A
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
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
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
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
12
Q
Icosahedral virion
A
- structure
13
Q
complex virus with binal symmetry
A
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
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
16
Q
Gigant viruses
A
- Most viruses fit through a 500-nm filter
- mimivirus does not; has a virion 150nm in diameter, genome
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
HIV infection compromises host immune system
- 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
HIV testing spread of AIDS
- 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
HIV infection cycle #1
- 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
HIV infection cycle #2
- Replication
- Reverse transcriptase
29
Evolution of HIV
- 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
AID treatments #1
- FDA lists 34 antiretroviral drugs used in AID therapy
-
31
Vaccine development for HIV has been unsuccessful
- Problem had been seen as high mutation rate
- Real problem is no vaccine yet has produced strong cellular immune respsonse
- Attenuated SIV vaccine
32
Influenza #1
- 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
Influenza #2
- 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
Viral recombinations has caused pandemics
- 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
New strains of flu
- 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
Emergin viruses
- Viruses that originate in one organism the pass to another and cause diseases
37
Ebola virus
- Cause severe hemorrhagic fever
- Among most lethal infectious diseases
- Lethality rates >90% in outbreaks in Africa
- Natural host in unkown
38
SARS coronavirus
- Seevere acute respiratory syndrome
- pneumonia-like symptoms, fatal in 8% of cases
- caused by coronavirus
- mutation rate loe
39
Viruses and Cancer
- Viruses may contribute to about 15% of all human cancers
- Viruses can cause cancer by altering
40
Prions
- "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
Viroids
- Tiny naked molecules of circular RNA
- Causes diseases in plants
- recent outbreak killed over 10 million coconut palms in the philipines
