Intro to Virology Flashcards
What is a virus?
Viruses are obligate intracellular parasites that cannot ‘live’ independently
-no independent metabolism and cannot replicate outside of living cells
What are bacteriophages?
Viruses that infect bacteria
Examples of commonality amongst viruses
-Capsid and nucleic acid material DNA or RNA
–some have lipoprotein layer and are called enveloped viruses
-Lytic and chronic lifestyles
-require host cells to reproduce
What are the steps in the lytic pathway?
- Attachment
- Penetration of nucleic acid material
- Synthesis of viral proteins and nucleic acids
- Assembly of new viruses
- Cell lysis and release of new virions
What does lysogenic mean?
Integration of the viral genome into the bacterial host genome and the virus can be vertically transmitted to new daughter cells
-Induction via stress or spontaneiusly to lytic pathway
Infection of eukaryotic host cells by influenza virus?
- Influenza virus becomes attached to target epithelial cell.
- The cell engulfs the virus by endocytosis
- Viral contents are released. Viral RNA enters the nucleus where it is replicated by the viraö RNA polymerase
- Viral mRNA is used to make viral proteins
- New viral particles are made and released into the ECF. The cell, which is not killed in the process, continues o make new virus
Examples of phages that infect E.coli?
-Phage Chi binds to the flagella
-Phage M13 binds to pili
-Phage MS2 binds to pili
-Phage T1 phage binds to OMPs
-Phage T4 binds to LPS
-Phage Phi174 binds to LPS
What is the firat and essential step of viral infections of host cells?
Receptor recognition by viruses
What is receptor recognition?
Key factor that dtermines host specificity and viral host range - if the viralrecüpetpor is specific to one species then virus will only infect one species
-if the virus is shared across multiple taxa then the virus can infect many species - broad host range
-has important implications for understanding disease outbreaks and predicting virus host jumps
How many viruses is there on the planet?
10*31
-most abundant biological entity on Earth
-All domains of tree of life can be infected by viruses
-Viruses account for 95% of total number of organisms present
-Bc viruses so small - amounmts to about 5% of total biomass
What is a virion?
-Functions to deliver viral genome into a host cell where it can be replicated
-when outside of living cells, viruses exist as particles - virus particle is called a virion
Herpes Simplex virus 1 vs Herpes Simplex virus 2
Herpesvirus virion
Herpes simplex virus 1 causes cold sores
Herpes simplex virus 2 causes genital herpes
What is included in Reoviruses?
Rotavirus - causes gastointestinal infections and diarrhea and is a major cause of infant mortality in developing countries
Ebola
-Discovered in 1976 when 2 consecutive outbreaks of fatal hemorrhage fever occured in diff parts of central africa
-Haemorrhage fevers - death in 65% of cases
-bats are resevoir hosts
-through humans- spread by contact with blood or body fluids or w bodies
What is a spillover event?
Occurs when an animal or person becomes infected with an ebolavirus through contact with resevoir host
What causes the Great Influenza Pandemic of 1918-1920?
Caused by the H1N1 influenza A virus
-earliest document was March 1918
How much of pathogens that cause emerging and re-emerging plant disease epidemics are viruses?
Nearly half - 47%
Viral Shunt in Marine Ecosystems
-In marine ecosystems, viruses infect and replicate within bacteria, phytoplankton and other mo
-When these infected cells burst open (lyse) they release their cellular components (carbon, N, phosphorus) into surrounding environment
-These nutrients can be recycled and used by other mo and can divert resources to higher organisms
How muc is estimated that through the lysis of pro cells, viruses relaease into global oceans
145 Gt C yr-1
Difference in lysogenic cycle?
-Phage plasmid enters and replicates with host DNA
In lytic cycle virus replicates inside host cell and bursts cell to release more virus
Lytic phage impact on bacterial evolution?
-Lytic phage can drive host evolution via natural selection for resistance evolution (lethal selection pressure like ABX)
-cycles of antagonistic coevolution - results in diversification of both bacteria and phage populations
Other evolution
-Horizontal gene transfer- many bacteria contain lysogenic or temperature phages that can integrate into host genomes
-The toxins of many pathogens are prophage encoded or phages derived - Cholera toxin and Shiga toxin
-Phages can also encode auxiliary metabolic genes (AMGs) that rewire host metabolism e.g viruses of cyanobacteria
What affect do viruses of cyanobacteria (cyanophages) have?
Carry photosynthetic genes that can account for mre than 50% of the expression of photosynthetic genes at the community level in oceans showcasing their capacity for diverting carbon to viral infected cells or virocells
What traces of viral DNA have been found in human genome?
-Retroviruses have infected germline cells leading to incorporation of viral DNA in genome of host organism - passed down and presenmt in human DNA
What are these viral sequences in DNA called?
Endogenous retroviruses (ERVs)
-Most are inactive or have accumulated mutations to make them non-functional but some may still be able to produce proteins or RNA
What are smallest infectious agents?
-Viroids (infectious RNA) and prions (infectious proteins)
Virion diameter
Virion - single viral particle
–vast majority fit range 25-100nm (0.025-1µm)
Cell diameter (bacterial, archaea and euk)
–vast majority 0.5µm-200µm
What is the genome size (length) of viruses?
-3-200Kb (ssDNA, dsDNA, ssRNA, dsRNA)
-Circovirus has a circular, ssDNA genome of between 1759 and 2319nt, making it possibly the virus of the shortest genome size in mammal viruses
DNA vs RNA
-Viral genome is encoded in DNA or RNA
-DNA and RNA can be single stranded or double stranded
-DNA and RNA can incorporate C,G and A
-Diff backbone sugar deoxyribose (DNA), ribose (RNA)
-Diff use of U/T nucleobase - uracil in RNA and thymine in DNA
-RNA is less stable - low fidelity
What is taxonomy and what is benefits?
-Order- family- genus- species
-Allows for standardized communication between scientists
-Simplifies classification of new organisms/species
What are biological species and who said this?
Ernst Mayr 1942
‘groups of interbreeding natural populations that produce viable offspring’
Definition of viral species?
A monopohyletic group of viruses that can be distinguished from those of other species by multiple criteria
Who discovered retroviruses and reverse transcriptase?
David Baltimore
-Baltimore classification of viruses
Which classes are DNA viruses and what are these?
Class I - classical semiconservative
Class II classical semiconservative, discard (-) strand
Class VII transcription followed by reverse transcription
Which classes are RNA viruses and what are these made up of?
Class III - make ssRNA (+) and transcribe from this to give ssRNA (-) complimentary strand
Class IV - make ssRNA (-) and transcribe from this to give ssRNA (+) genome
Class V - make ssRNA (+) and transcribe this to give ssRNA (-) genome
Class VI - make ssRNA (+) genome by transcription of dsDNA
What does the Baltimore classification base of off?
Categorizing viruses based on their genome type and replication strategy
Group I examples
Double stranded DNA viruses
e.g herpesviruses, adenoviruses and poxviruses
Group II examples?
Single stranded DNA viruses (serves as atemplate for transcription)
e.g parvoviruses
Group III
Double-stranded RNA viruses (dsRNA)
e.g reoviruses
Group IV
Positive - sense single stranded RNA viruses (+ssRNA) - functions as mRNA upon entry into host cell
e.g picornaviruses, flaviviruses and coronaviruses
Group V
Neg-sense single stranded RNA (-ssRNA) - have single strand RNA genome that is complimentary to MRNA
e.g influenza virus and paramyxoviruses
Group VI
Reverse-transcribing viruses
-use reverse transcriptase enzyme to convert their RNA genome into DNA upon infection
e.g HIV
Group VII
Double stranded DNA viruses with a RNA intermediate - consists of viruses that have a DNA genome but replicate through an RNA intermediate
e.g hepatitis B
