Lecture 13 and 14 Flashcards
What was the first virus to be discovered?
Tobacco mosaic virus
What does tobacco mosaic virus do?
Causes tobacco leaves to be mottled, stunts growth
Who was the first person to investigate TM disease?
Adolf Mayer
What did Adolf Mayer find could transfer the disease?
Diseases could be transferred in sap between plant
What could Adolf Mayer not find?
Anything microscopic in the sap causing the disease (something submicroscopic was causing the disease)
Who filtered the sap?
Dmitri Ivanovsky
What did Dmitri Ivanovsky find when he filtered the sap?
It could still transfer the disease
What did the fact that filtered sap could transfer disease suggest?
It was sub-microscopic or a toxin
Who discovered that the disease could replicate and therefore was not a toxin:?
Martinus Beijerinck
How did Martinus Beijerinck conclude the virus can replicate?
Filtered sap causes mottled leaf appearance in a third plant- therefore toxin was not responsible for transmission
Who tried to culture bacteria from the infected tobacco plant?
Martinus Beijerinck
What did the fact that Beijerinck’s cultures didn’t grow suggest?
Disease not caused by cultivable bacteria
How did Beijerinck definitively show that tobacco mosaic disease was not caused by a bacterium?
He treated the sap with ethanol to damage the membrane. The sap was still infectious, therefore not bacteria
Who first isolated and crystallised TMV virion?
Wendell Stanley
What did Stanley’s crystallized virus remain?
Infectious
What did the fact that TMV remained infectious demonstrate?
Viruses have no independent metabolism
Who first viewed TMV virion? How?
Kausche, Pfankuch and Ruska
Electron microscope
What is the average virus size?
20nm diameter to 1000nm length
What is the cultivable nature of viruses?
Obligate intracellular parasites
What bacteria share small size and cultivatable nature of viruses?
Rickettsia/ Chlamydia
What is the cell structure of viruses?
No cellular structure (acellular)
What is the protein coat around a viruses genome called?
Capsid
What genome do viruses have?
A single type of nucleic acid (RNA or DNA)
What is a envelope?
A lipid layer surrounding the capsid
What does synthesis result in?
Specialised structures that transfer viral genome to other host cells
Generally, where do enveloped viruses come from?
Animal cells with no cell wall
Why can’t most drugs interfere with viral multiplication?
Would affect host cell function, host enzymes are used to generate the parasites
What name is given to viruses that infect fungi?
Mycoviruses
What host range do most viruses have?
Limited to usually one host species, specific cell types
What virus causes glandular fever?
Epstein-Barr virus
What phages infect Escherichia coli?
T-even phages (T2, T4)
What cells does influenza A virus infect?
Nose/throat/lungs epithelial cells
What cells does Epstein-Barr virus infect?
B-lymphocytes
Why is virus host range limited?
Virus requirements: specific receptor/ligand for cell invasion
Need certain host factors for viral replication
Name a virus that can jump species and expand their host range.
Influenza A virus (has several variants (serotypes))
What type influenza A serotype infects birds?
H7N7
What serotype of influenza A infects pigs?
H1N1, but can act as a reservoir for all serotypes
What serotype of influenza A virus infects humans?
H3N3
Why are emerging diseases a big problem?
No natural defenses: we haven’t adapted to these diseases
What are the 2 life cycle stages for viruses?
Replicating stage, birion
What is the replicating stage?
Genome replicating
Active, intracellular disease causing stage
What is the virion stage?
Dormant, transmissible stage, survives outside host
What is the core of a virion?
Nucleic acid (DNA or RNA)
What is the capsid composed of?
Subunits called capsomeres
What makes up the capsomeres?
Some viruses, made of one protein
Other viruses, capsomere made of several proteins
How does the capsid get put together?
It is self assembling
What gives the virus a shape?
The capsid
What shape can viruses be?
Helical, complex, polyhedral
How are capsomeres arranged in helical viruses?
Arranged in a spiral (coil like)
What shape do capsomeres form in polyhedral viruses?
Equilateral triangle, which arrange into polyhedral
Most polyhedral viruses are ______ shaped.
Icosahedral (20)
What is the enveloped derived from?
Host membrane
What can the envelope contain?
Glycoproteins (spikes) encoded by viral and host genome
What do spikes on the envelope do?
Function as antigens: involved in host cell invasion and identification
What is the other function of the envelope?
Protect virion from enzymes/chemicals
Name two enveloped viruses
Influenza
HIV
What viruses carry appendages?
Complex viruses (particularly bacteriophages)
What do appendages do?
Used to attach virus to host cell
Name a non-enveloped polyhedral virus.
Poliovirus
Name an enveloped polyhedral virus
Herpes simplex virus
Name a non-enveloped helical virus
TMV
What shape are viral genomes?
Circular or linear (nucleic acid type irrelevant)
Viral genomes can be _____ or __-______
Segmented
Non segmented
What is a segmented viral genome?
Several nucleic acid molecules, such as some RNA viruses
What are non-segmented viral genomes?
Single nucleic acid molecule (most DNA viruses, some RNA viruses)
Single stranded (ss)RNA viruses can be:
+sense
or
-sense
What is +ssRNA?
Can be translated directly by host cell
What is -ssRNA?
Converted to +sense before translation
How is the + strand made from the - strand?
RNA polymerase synthesises it
What must -ssRNA also encode?
RNA polymerase
What are two classification systems used to classify viruses?
International committee of taxonomy of viruses
Baltimore classification
What does ICTV use?
Nucleic acid type, site of replication, morphology and pathology
What is the taxonomic structure of viruses?
Order
Family
Genus
Species
What does baltimore classification do?
Take into account unassigned viruses of ICTV
Based on how viruses generate mRNA
What 7 groups are baltimore classified viruses split into?
dsDNA, ssDNA, dsRNA, +ssRNA, -ssRNA, +ssRNA-RT, dsDNA-RT
Give an example of a virus that undergoes the lytic cycle.
T-even bacteriphage
What are the 5 stages of the lytic cycle?
Attachment Penetration Biosynthesis Maturation Release
What enzyme degrades the cell wall of the host when the baseplate of the virus makes contact with the cell wall?
Lysozyme
Gene expression is ______, it is not expressed at the same time
Temporal
What are the early genes?
Viral genome replication
What happens to host DNA?
Viral-induced degredation
How does host protein biosynthesis stop?
Viral proteins interfere/repress host translation
How long does the lytic cycle take?
About 30 minutes
What enzyme breaks down bacterial cell wall during release?
Lysozyme
Name a lysogenic phage.
E.coli bacteriophage lambda
What are the 7 stages of lysogenic cycle?
Attachment Penetration Integration/dormancy Excision Biosynthesis Maturation Release
What is the first stage of integration?
The viral genome circularises
What is the inserted viral DNA called?
Prophage
Why are there differences between bacteriphages and animal viruses?
Envelope/non-envelope
Genome structure
What are the 6 stages of animal virus replication?
Attachment Entry Uncoating Biosynthesis Maturation Release
Uncoating in animal viruses means that…
can get dormancy phase for some animal viruses (latent disease)
What are virion ligands in animal viruses?
Spikes (enveloped)
Fibres (non-enveloped)
What happens during attachment of enveloped viruses?
Specific receptor/ligand interaction
What happens during fusion entry of enveloped viruses?
Fusion: host cell membrane/viral envelope fuse, capsid released into cytoplasm
What happens during endocytosis/pinocytosis entry of enveloped viruses?
Attachment can trigger endocytosis or ‘feeding’ mechanism pinocytosis
What happens during uncoating?
Enzyme mediated degredation of capsid to release viral genome
What may the uncoating enzyme be of?
Viral origin (poxviruses) Host origin
How do non-enveloped viruses fuse?
Host cell membrane/viral capsid fuse, viral genome released into host cytoplasm
Where do RNA viruses multiply in animals?
The cytoplasm
What ways are animal viruses release?
Budding (enveloped), rupturing (non-enveloped viruses)
How does budding work?
Capsid associates with and adheres to portion of the host plasma membrane to virus to form a bud
What stages do antivirals attack?
Uncoating, viral biosynthesis (nucleic acid replication and protein processing)
Release
