Bms1026 Viruses

Front 1

Importance of viruses

Back 1

- Biological control: specific viruses to target pests

Front 2

How to study viruses

Back 2

- need host cells to multiply so have to maintain virus within embryonic eggs, cell cultures or living plants/animals
- Plaque method: monolayer of cells on plate, virus cells clear area by destroying cells by lysis creating clear plaques which can be seen

Front 3

Fighting viral disease

Back 3

- cant use antibiotics as have no metabolism (are inert) and most other drugs interfere with host cells as well so are to toxic to use
- VACCINATIONS: introduce attenuated, dead, inert, fragment of virus to create an immune response which is remembered by memory cells incase of secondary infection
- other methods: antiviral drugs, slaughter/isolate infected animals, control vectors, infection control in hospitals.

Front 4

What are viruses?

Back 4

- are very small (filterable) and are OBLIGATE INTRACELLULAR PARASITES (need host), have small genome (3-300kb), no metabolism
- have either DNA or RNA (never both)
- contain protein coat
- multiply within hosts synthesising machinery
- range from 20-225nm diameter

Front 5

4 main structures

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- tobacco mosaic virus: spiral RNA core surrounded by protein coat to form a hollow tube
- adenovirus/polyhedral: DNA core surrounded by protein capsome with protruding glycoproteins
- influenza: RNA surrounded by protein capsid, with a membrane envelope with protruding glycoproteins
- bacteria phage: DNA in head, long sheath with tail filaments and pins

Front 6

How are viruses constructed?

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- virus taken into host cell
-viral DNA transcribed into RNA and replicated DNA
- RNA translated into proteins which are synthesised into capsids and joined with DNA to form protein units
- virus released by lysis
(virus uses hosts enzymes, ribosomes, nucleotides, energy etc)

Front 7

Lytic cycle of phage T4 (virulent phase)

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1) attachment: the T4 uses its tail fibres to bind to specific to specific receptor sites on E.coli surface
2) entry of phage DNA + degradation of host DNA: the sheath of the tail contracts, injecting DNA and causing host DNA to hydrolyse
3) synthesis of viral genomes & proteins: phage DNA directs production of proteins & genome by host enzymes, using components within the cell
4) assembly: 3 separate sets of proteins self-assemble to form phage heads, tails and fibres. the phage genome is packaged inside the head
5) release: the phage directs production of an enzyme that damages the cell wall allowing fluid to enter and the cell to swell and burst releasing the phages

Front 8

Lysogenic cycle of phage T4 (latent phase)

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1) viral DNA incorporated into the hosts DNA
2) when host replicates, so is the viral DNA but no particles are released
3) remains dormant as latent phase
4) latent viruses can be activated by stress and complete lytic cycles

Front 9

Extracellular Vs intracellular

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- EXTRACELLULAR: microscopic particle containing nucleic acid surrounded by a protein coat or other macromolecules (VIRION = the infectious virus particle is metabolically inert and cannot produce energy or biosynthesis - can contain enzymes that the host doesnt have)
- INTRACELLULAR: when virus is in the host cell and replicates

Front 10

Symmetry types

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- spherical viruses have icosahedral symmetry
- rod shaped viruses have helical symmetry

Front 11

Viral proteins

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- EARLY proteins: synthesised soon after infection which are necessary for replication
- LATE proteins: proteins for capsid

Front 12

Genetic material type

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- can be DNA or RNA, single or double stranded wit positive (same orientation as mRNA or negative complementary to mRNA)
- depending on type may need transcribing before use as mRNA or need reverse transcription etc