Viruses Flashcards
What are bacteriophages, and how their structures is different from other human and animal viruses?
- bacteriophage = viruses that lyse bacteria
Animal viruses capsid enters the cell, bacteriophage do not penetrate
how do viruses recognise and bind to their specific host cells?
Cellular receptor
What is not encoded in viral genomes? why are they not present?
complete protein synthesis
proteins involved in cell wall production or membrane biosynthesis
No centromeres or telomers found in standard host chromosomes
- not there because host cell has them
capsomeres?
Subunit of the capsid
Smallest morphological unit visible with an electron microscope
what is arranged in in icosahedral symmetry? what is arranged in helical?
protein subunits of round viruses
why?? = regular stable structure from the smallest number of proteins (60 identical subunits)
protein subunits of rod shaped viruses
what is meant by a virus’s particles being metastable
stable because they protect - capsid
unstable because they dissociate to give genetic information into cell
three types of capsid structures or viruses
Helical, Icosahedral, Complex
Structural Subunit of capsid definition
unit from which the capsid is built- one or more subunit
Why do you think capsid is made of one or few proteins that repeat over and over?
allow metastability
easy to break but still stable
Give examples of the different types of proteins that are encoded for by the viral genome?
Structural proteins
Capsid proteins, VAPs
Viral replication: DNA polymerase, RNA polymerase
Pathogenesis
Transformation (HPV and Cervical cancer)
Modulation of host defences
what are the Main Criteria for classification of viruses?
Nucleic acid
Capsid symmetry
Presence or absence of lipid envelope
why can -RNA not be used as mRNA but +RNA can?
+RNA has N Sequence identical to the sequence of mRNA whereas –RNA has a sequence that is complementary to the mRNA and cannot act directly as mRNA, it must first be converted to or replicated to +RNA using RNA poly , and only then it can act as mRNA.
what makes viroids and prions unconventional viruses?
- viroids contain no proteins just 70% of the nucleotides in the genome RNAs are base-paired - 220 to 400nt
- prions = no nucleic acid - jus a protein
What is the basis of Baltimore system in classifying viruses?
the way the virus makes mRNA
Identify & describe the major steps in viral replication and use examples
- Recognition
- Attachment
-Entry/penetration
Enveloped: Fusion proteins (HIV) or endosomes /ph change (Influenza)
naked: Endocytosis or Direct (Poliovirus)
-Uncoating
-Protein & NA synthesis
-Assembly
-Release - bud or lyse
define Viral Tropism
The specificity of a virus to a specific host
how do dsDNA viruses replicate their DNA?
The viral genome is copied or replicated by the DNA polymerases to produce many dsDNA copies
dsDNA - packaged with the viral proteins = many new viral particles/virions
What are the different strategies that viruses used to enter the host cell?
there are two ways:
In viral infections, what determines the host and cell range? Give examples
–
What are the steps of viral replication?
What aspect of the life cycle of a virus leads to the sudden increase in the growth curve?
the bursting of the host cell that releases all the viral particles
What are the main methods of quantifying viruses and how they differ from each other?
titre is the main method – many times the main one is a plaque assay but if the virus does not produce these holes in solution, then another method (pathogenicity assays) such as TCID50, AID50 ,LID50assays
are used.
What is meant by CPE, give some examples
CPE = Cyto Pathic Effects –> Distinct observable cell abnormalities/changes in the cells due to viral infection
How would you detect non-CPE producing viruses?
Plaque asset relies on CPE –> another method such as EM or Combination of cell culture with PCR has permitted detection of infectious viruses that grow slowly, or fail to produce CPE.
What are the main advantages of cell culture for virus growth
determine the causative agent of a disease
study its structure, replication, genetics, its effects on host cells,
Vaccine production
How can you use hemadsorption to identify viruses?
it determines if a virus is able to bind to RBCs on red blood cells
What characteristics must a gastrointestinal virus possess in order to effectively infect through this route,
not have a capsule as it is dissolved by the harsh conditions of the stomach or bile in the small intestine
What is the difference between a susceptible cell and a permissive cell?
Susceptible cell:
Expresses the specific receptors that are recognised by a specific virus through specific VAPs
Permissive cell:
Contains the proteins and molecules within the cell that are necessary for replication to occur.
What are the different portals of exit of viruses
Skin - HPV
GI tract - Poliovirus, rotavirus
Genital tract - HIV, HSV
Conjunctiva - Adenovirus
Viremia - blood
Uraemia - urine
What is the difference between pathogenesis and virulence
pathogenesis: The ability/capacity of the virus to cause disease
Quantitative or relative measure of the pathogenesis of the infecting virus: Virus A is more virulent than virus B
Give specific examples of each of the mechanisms used by viruses to cause injury to cells or tissues
4 broad groups:
- Direct cytotoxicity of the virus
- Virus-induced immunopathogenesis
- Virus-induced immune suppression
- Virus-induced transformation
What is the different between HIV and AIDS?
HIV = virus that infects human
AIDS = the last stage of the three staged of HIV infection where the patient experiences immune system failure
-“characterised by increased susceptibility to opportunity infections”
How does AIDS develop?
three stages
1. acute stage where the HIV infects CD4+ T cells (possible decrease but not enough to see)
- chromic phase - virus spread & infect helper T cells - Macrophages - dendritic cells –> virus = contained in lymphoid tissue
- AIDS stage - cell destruction + decline in CD4+ T cells in blood
immune - opportunistic infections
What is the difference between inactivated vaccines and subunit vaccines?
inactivated: contain whole virus which has been killed or have been altered, so that they cannot replicate
subunit: one or more specific component/ unit/antigens usually from the surface of the virus
Give examples of viral infections that can be treated by antiviral drugs
HIV - Maraviroc /Selzentry or HAART
influenza - AMANTADINE & RIMANTADINE
herpes simplex II - acyclovir
HIV,HCV, Herpesviruses- persistent infections
What are the different routes of transmission of viruses?
Vertical transmission
respiratory tract
GI (gastrointestinal) tract
genital tract
How can virus transmission be interrupted?
By 3 methods:
interruption
Vaccination
