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.
