35.3 Virion Structure and Classification Flashcards
What is the size of viruses?
20 - 300 nm
What visual techniques are used to study viruses?
- Electron microscopy has in the last 50 years developed sufficiently good resolution to view viruses
- X-ray crystallography is also useful in understanding the structure of viruses
Can viruses be detected by a light microscope?
No, only electron.
What is the system for classifying bacteria called and what is it based on?
- Baltimore system
- Based on the way in which a virus generates mRNA from its genome
How is the simplicity of viruses compared to other organisms reflected in their structure and function?
*Limited range of functions (no need for nutrition/ excretion/ independent reproduction)
*Formed from protein w/ RNA or DNA polynucleotides with very limited lipid and carbohydrate structures.
Where does the diversity of viruses come from?
Structure, host target, and disease.
Where is the genetic material of virions stored?
In nucleocapsids.
What is the nucleocapsid region?
A protein coating containing the polynucleotide sequence used by the virus to code for necessary proteins.
How are some viruses able to have an envelope?
Some viruses are encapsulated - they have a lipid bilayer derived form the host cell during viral budding at the end of the replication stage of the life cycle.
What can be inserted into the viral envelope?
Viral attachment proteins - these can assist with entry to cells and mediation of viral effects.
What are the viral attachment proteins susceptible to? Give an example.
Can be targeted by non-specific host defences/ detergents (e.g. bile salts in gut ileum are able to emulsify envelope + break it down, leaving virion vulnerable to proteolytic enzymes present in the gut)
What are the different characteristics of viral genetic informatiom?
Presence of RNA/ DNA, segmentation, positive or negative polarity
What does the positive/ negative polarity refer to?
The direction of the strand.
* The negative strand is the one used as a template for mRNA synthesis
* The positive strand is the one that corresponds in sequence to the mRNA sequence that is transcribed from the negative strand
Explain the concept of segmentation in viruses.
In viruses, the DNA may be divided into more than one section, which is referred to as it being segmented.
What is the nucleic acid type and replication strategy for Group 1 of the Baltimore classification?
*dsDNA
*RNA polymerase to produce mRNA
What is the nucleic acid type and replication strategy for Group 2 of the Baltimore classification?
*ssDNA
*Converted to dsDNA then transcribed
What is the nucleic acid type and replication strategy for Group 3 of the Baltimore classification?
*dsRNA
*RNA polymerase to produce mRNA
What is the nucleic acid type and replication strategy for Group 4 of the Baltimore classification?
*+ssRNA
*Copied into -ssRNA before transcription into mRNA
What is the nucleic acid type and replication strategy for Group 5 of the Baltimore classification?
*-ssRNA
*RNA polymerase to produce mRNA
What is the nucleic acid type and replication strategy for Group 6 of the Baltimore classification?
*+ssRNA w/ rt
*Reverse transcriptase to produce dsDNA then transcribed into mRNA
What is the nucleic acid type and replication strategy for Group 7 of the Baltimore classification?
*dsDNA w/rt + ssRNA intermediate
*Transcribed by host cell’s RNA polymerase. In replication, reverse transcription used to renew DNA genome.
Baltimore class I examples
Adenoviruses, pox viruses, HSV (HHV-1/2)
Baltimore class II examples
Parvoviruses
Baltimore class III examples
Reoviruses (rotavirus)
Baltimore class IV examples
Poliovirus, hepA, flaviviruses (HCV), calciviruses (norovirus), SARS-CoV-2
Baltimore class V examples
Orthomyxoviruses (influenza), paramyoxviruses (measles, mumps, RSV), rabies
Baltimore class VI examples
Retroviruses (HIV, HTLV-1)
Baltimore class VII examples
HepB
