Flashcards
DNA IX - Viruses, Viroids, and Prions
Cards in this deck (38)
- 1What is a virus?One or more nucleic acid molecules within a coat protein
- 2What is characteristic of a virus? (5)Can evolve and replicate
No ribosomes
Contains DNA/RNA or both
Are insensitive to changes in its environment
Affect organisms from all domains of life - 3Why are viruses relatively insensitive to changes in their environment?As they can't synthesise their own proteins, they can't translate heat shock genes into proteins or lac genes etc.
- 4What is the general structure of a virus? (5)Capsid usually made from capsomere proteins
Nucleic acid
May contain virus enzymes
Glycoprotein spikes
May have dsDNA/ssDNA/dsRNA - 5What additional structure might a virus have?Virus may be naked or enveloped by a lipid membrane acquired from the cell or nuclear membrane from an infected cell.
- 6What projections are seen from this additional layer?Virus specific proteins
- 7How do viruses acquire this layer?Membrane acquired as the virus leaves the host cell
- 8Draw a diagram showing this process.Capsid/cytoplasm/viral-encoded g.spikes/cell membrane/viral genome encodes for insertion into the host cell's membrane etc.
- 9What types of different geometrical arrangements can the capsid form?Helical capsid
Icosahedral capsid
helical capsid (enveloped sphere)
complex capsid (bacteriophage)
Pandoravirus - 10Describe the generic life cycle of a virus with a DNA genome (4)1. Entry and uncoating
2. replication
3. transcription and manufacture of capsid proteins.
4. Self-assembly of new virus particles and exit from cell. - 11Name the different types of viruses with RNA genomes (3)dsRNA genomes
+ssRNA
-ssRNA - 12Describe how +ssRNA viruses work.ssRNA strand can store info or act directly as mRNA.
- 13Describe how -ssRNA viruses work.Genome is complementary to mRNA, can act as a template
- 14Draw an annotated diagram describing the initiation of replication in a +ssRNA virusViral RNA + strand acts as a template for translation
Creates capsid and RNA-dependent RNA-Polymerase - 15Describe the transcription process.RNA-dependent RNA polymerase synthesises RNA complementary to the viral genome (-) strand
- 16Describe the final step in this replicationRNA-dependent RNA Polymerase uses the (-) strand as a template to synthesise new copies of the viruse genome
(+) strand is regenerated - 17What happens at the end of replication?Assembly of new virus particles.
Newly formed virus buds off from cell. - 18Describe the genome of a HIV virusContains 2 identical ssRNA genomes, like we have 2 copies of the same gene on chromosomes.
- 19What is the first step in HIV infection?Entry - viral membrane fuses with membrane of the cell
RNA molecules released - 20What is the second step in HIV infection?RNA reverse-transcriptase synthesises a DNA copy complementary to the RNA molecules which form a RNA-DNA hybrid
- 21What is the third step in HIV infection?RNA side of the hybrid is replace by DNA
The newly formed dsDNA is introduced at a random site of the chromosome - 22What is the forth step in HIV infection?DNA can now be transcribed from the chromosome to make mRNA that translates for the capsid and glycoprotein spikes
RNA genome is also transcribed - 23What is the fifth and final step in HIV infection?Virus is formed, buds off from cell.
- 24What are Viroids?Infectious agents without a protein coat
- 25What is characteristic of the infectious agent? (4)A circular, ssRNA molecule ~350nc in length with substantial internal base-pairing.
The RNA replicates inside the infected host cell
No 5'-3' polarity - 26What are prions?Infectious agents without DNA or RNA
- 27What type of disease do prions cause?Transmissable Spongiform Encephalopathies (TSE)
- 28What are the effects of TSEs?Fatal and untreatable neurological deterioration.
- 29What is diagnostic of prion infection? (2)Very extensive neuronal death
Spongiform degeneration (vacuolation) of the brain - 30Name 2 examples of TSEs in farm animalsScrapie - sheep and goat
Bovine spongiform encephalopathy (BSE) - 31Describe an example of a TSE in humansCreutzfeld-Jakob disease - arises in middle and old age
Most causes sporadic, a few transmitted (i.e. through contact with contaminated growth hormone.) - 32Describe an example of a TSE in humansFatal familial insomnia -
A dominant genetic disorder that can be transmitted by injection affected brain tissue into healthy subjects. - 33Describe the characteristics of prionsSmaller than viruses so pass through anti-viral filters of the cell
Very heat resistant
Very resistant to radiation - 34What are prions believed to be formed from?Believed to be mis-folded versions of a normal cellular protein (The prion protein (PrP))
Mutations in the gene encoding the prion protein may make it more likely to mis-fold spontaneously, accounting for inherited TSEs - 35Compare normal and misfolded prion proteinsProtease sensitive ¬ Protease resistant
High a-helix content (42%) ¬ low a-helix content (30%)
Low b-sheet content (3%) ¬ high b-sheet content (43%)
soluble ¬ insoluble due to high b-sheet content, produces extracellular deposits
Does not aggregate ¬ aggregates into fibres - 36What are the names of these extracellular deposits?Amyloid plaques
- 37Draw an annotated diagram showing prion replication in TSEs.Normal cell:
PrP gene -> mRNA -> normal PrP
during TSE infection:
Prp gene -> mRNA -> normal PrP -> abnormal accumulations -> infecting mis-folded PrP -> abnormal accumulations
Confirmational change
infecting mis-folded PrP causes correctly folded protein to mis-fold. - 38Draw an annotated diagram showing inherited TSE forming mis-folded PrPs.Mutant prion protein gene -> mRNA -> PrP with reduced stability and/or incrased propensity to misfold -> mis-folded PrP -> accumulation
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- User has deleted their subject information Flashcards on DNA IX - Viruses, Viroids, and Prions, created by Deleted user on 27/12/2017.
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- Created by J yadonknow · Dec 27, 2017
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