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Flashcards by J yadonknow, updated more than 1 year ago
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Created by J yadonknow
almost 7 years ago
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| Question | Answer |
| What is a virus? | One or more nucleic acid molecules within a coat protein |
| What 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 |
| Why 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. |
| What 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 |
| What 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. |
| What projections are seen from this additional layer? | Virus specific proteins |
| How do viruses acquire this layer? | Membrane acquired as the virus leaves the host cell |
| Draw 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. |
| What types of different geometrical arrangements can the capsid form? | Helical capsid Icosahedral capsid helical capsid (enveloped sphere) complex capsid (bacteriophage) Pandoravirus |
| Describe 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. |
| Name the different types of viruses with RNA genomes (3) | dsRNA genomes +ssRNA -ssRNA |
| Describe how +ssRNA viruses work. | ssRNA strand can store info or act directly as mRNA. |
| Describe how -ssRNA viruses work. | Genome is complementary to mRNA, can act as a template |
| Draw an annotated diagram describing the initiation of replication in a +ssRNA virus | Viral RNA + strand acts as a template for translation Creates capsid and RNA-dependent RNA-Polymerase |
| Describe the transcription process. | RNA-dependent RNA polymerase synthesises RNA complementary to the viral genome (-) strand |
| Describe the final step in this replication | RNA-dependent RNA Polymerase uses the (-) strand as a template to synthesise new copies of the viruse genome (+) strand is regenerated |
| What happens at the end of replication? | Assembly of new virus particles. Newly formed virus buds off from cell. |
| Describe the genome of a HIV virus | Contains 2 identical ssRNA genomes, like we have 2 copies of the same gene on chromosomes. |
| What is the first step in HIV infection? | Entry - viral membrane fuses with membrane of the cell RNA molecules released |
| What 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 |
| What 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 |
| What 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 |
| What is the fifth and final step in HIV infection? | Virus is formed, buds off from cell. |
| What are Viroids? | Infectious agents without a protein coat |
| What 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 |
| What are prions? | Infectious agents without DNA or RNA |
| What type of disease do prions cause? | Transmissable Spongiform Encephalopathies (TSE) |
| What are the effects of TSEs? | Fatal and untreatable neurological deterioration. |
| What is diagnostic of prion infection? (2) | Very extensive neuronal death Spongiform degeneration (vacuolation) of the brain |
| Name 2 examples of TSEs in farm animals | Scrapie - sheep and goat Bovine spongiform encephalopathy (BSE) |
| Describe an example of a TSE in humans | Creutzfeld-Jakob disease - arises in middle and old age Most causes sporadic, a few transmitted (i.e. through contact with contaminated growth hormone.) |
| Describe an example of a TSE in humans | Fatal familial insomnia - A dominant genetic disorder that can be transmitted by injection affected brain tissue into healthy subjects. |
| Describe the characteristics of prions | Smaller than viruses so pass through anti-viral filters of the cell Very heat resistant Very resistant to radiation |
| What 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 |
| Compare normal and misfolded prion proteins | Protease 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 |
| What are the names of these extracellular deposits? | Amyloid plaques |
| Draw 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. |
| Draw 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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