Viruses 2 Flashcards
Helical capsid structure?
Capsomeres are arranged in a helical array to form a hollow cylinder
What does the surface of each capsomere contain in a helical capsid?
a ridge in which the viral genome is embedded
Issue with identifying viral capsids?
The shape is not always evident e.g. influenza generates a helical capsid but looks spherical when imaged using EM
Why does influenza appear spherical
It has a helical capsid, surrounded by a lipid envelope
How do some viruses break up their genomes?
Viruses like influenza (e.g. 8) have their genomes on several distinct strands of DNA and RNA
Viral genome size?
V small compared to other genomes–> cauliflower mosaic virus only codes 7 genes
Mimivirus genome size?
V large–> 1.2Mb
How do viruses encode a lot of genes on a small strand of DNA/RNA?
They often contain overlapping genes
Why is classifying viruses important?
important in understanding the properties of different viruses, especially newly discovered viruses
HIV-1 classification example?
Morphological and genetic characterisation of HIV-1 revealed it was in the Retroviridae family–> allowed important features to be ID’d ab it and others in the same group
How were viruses first classified?
The diseases they caused and the symptoms of these diseases
Issues with classifying viruses based on symptoms?
Dissimilar viruses can cause the same symptoms, and similar viruses can cause diff symptoms
Bacterial cause of issue with classifying viruses based on symptoms?
Some symptoms associated with viral infections may be due to secondary bacterial infections, not the virus itself
Example of viruses that cause similar symptoms but are structurally and replicatively different?
Hepatitis viruses (A,–>E)
Non-enveloped hepatitis viruses?
A and E
Enveloped hepatitis viruses?
B, C, D
What is hepatitis?
inflammation of the liver
What is the ICTV?
International Committee on Taxonomy of Viruses
What is ICTV classification based on?
Genome composition and structure, capsid symmetry, envelope, size of viral particle and host range
Most important aspect of viral classificaiton?
Genome composition
Why is genome composition the most important part of viral classificaiton?
Viruses that have similar genome sequences are likely to share a common ancestry
How did David Baltimore propose viruses should be expressed?
Genome composition and how they express mRNA and replicate their genome
Diff type of nucleic acid that viruses can have?
ssDNA, dsDNA, ssRNA (+ve sense), ssRNA(-ve sense), dsRNA
Single sense stranded nucleotides can then also be positive sense or negative sense
What will be produced if a +ve sense strand is copied?
The complementary -ve sense strand
