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53 Cards in this Set
- Front
- Back
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Are bacterial viruses host dependent? |
Yes |
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What does host dependent mean? |
Cannot survive without infecting bacteria Require host machinery to produce progeny phages |
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What is host specificity |
Each phage has its specific range of host bacteria |
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Are they beneficial to the host? |
No, they are harmful to their hosts |
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What is the most abundant and diverse form of DNA replicating agent on the planet? |
Marine phages |
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What is the ratio of marine phage to ocean in 1ml? |
5x10^7 per ml |
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What do marine phages do for bacterial population explosions? |
Essential in preventing bacterial population explosions (algal blooms) |
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Who discovered marine phages? |
Twort and d' Herelle independently |
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What is the most common genome of phages? |
dsDNA genomes |
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Name the parts of a virus |
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How many tailed phages are there? |
4900 |
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How many phages in total? |
5100 |
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What are the categories in categorising a phage? |
Host bacteria, genome, morphology, ability to lysogenise |
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What are the 3 basic types of phage? |
Tailed phages (dsDNA) Filamentous phages (ssDNA) Icosahedral phages (ssDNA, ssRNA, dsDNA) |
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Example of lambda phage |
Linear dsDNA, icosahedral lysogenic cycle |
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How much average size gene products do simple phage have enough nucleic acid to code for? |
3-5 average size gene products |
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How many gene products do more complex phages have to code for? |
over 100 gene products |
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What do tail fibres attach to? |
Specific receptors |
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What are some examples of specific receptors? |
Surface proteins, LPS, pili and lipoprotein |
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What is the role of the sheath? |
Serves as a channel for DNA/RNA injection |
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3 characteristics of the lytic cycle |
+lysis of host and release progeny particles +viral genes fully expressed +virulent phage |
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What are 3 characteristics of the lysogenic cycle? |
+phage DNA inserted into the host chromosome sometimes at a specific site-prophage +most of phage functions are switched off +temperate phage |
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What are the 5 stages of the infection of host cells by phages --lytic cycle ? |
1. Adsorption 2. Injection fo genomic nucleic acid 3. Transcription & Translation 4. Replication of DNA 5. Maturation & release |
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3 characteristics of adsorption? |
Highly specific Interaction between tail & cell surface receptors Host range mutation may occur in phages |
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What did the Hershey and Chase Experiement (1952) show? |
The material inside the virus is not proteins but nucleic acids (genetic information) |
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4 steps in viral injection of DNA |
Landing, pinning, tail contraction and penetration & DNA injection |
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What are the 3 types of genes in sequential transcription of phage genes (Transcription & translation- 1) |
Immediate early and delayed early genes Middle genes- transcribed throughout infection Late genes |
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What occurs in immediate early and delayed early genes? |
Shut off cellular macromolecule synthesis Replication of phage DNA |
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What occurs in middle genes- transcribed through infection? |
DNA replicates and recombines |
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What occurs in late genes? |
Capsid proteins & enzymes for lysing cells |
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What else occurs in transcription and translation? |
utilisation of ribosomes |
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What is the main component of the head capsid? |
Most abundant T4 protein |
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Describe the viral DNA replication- M13 |
Host enzymes carring in the infecting ss viral genome and a duplex DNA replicative form Replication occurs (bi-directoinal ori) Gene II nicks + strand rolling in a circle replication Gene II nicks completed + strand and circularisatoin of completed + strand |
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What occurs during maturation and release? |
Assembly of the capsid
Association of DNA and capsid Lysis of cells and release of phages (~100 progeny phage released, each cycle 45-60mins) |
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What forms when there is bacteria + phage after phage plaque formation? |
lysis can be seen- where all the bacteria have died as the phage killed it |
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What is lysogeny? |
The indefinite persistence of the phage DNA in the host cells, without phage production |
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What can temperate phages produce? |
phenomenon of lysogeny
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What are prophages? |
Integrated, noninfectious form of phages |
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What is repression? |
Phage inserts itself via integration to host's chromosome to be replicated everytime bacteria replicates |
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What is a repressor? |
Phage coded protein that binds to a site on the phage DNA (operator) |
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What is the role of the repressor? |
Shuts off transcription of most phage genes except repressor gene |
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Is repression specific? |
Yes, immunity to superinfection with same phage |
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Describe integration of DNA into bacterial chromosome |
Cut & paste of DNA , recombination |
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What are some phage resistant systems? |
Blocking of phage DNA injection Abortive infection systems Evolutionary arms race between bacteria and their phages |
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What is the abortive infection system? |
interfering with phage DNA replication, RNA transcription, phage development and morphogenesis |
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What is naturally occurring phage resistance |
Adsorption interference DNA injection inhibition Restriction/modification (R/M) Abortive infection (Abi) |
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What is genetically engineered phage resistance? |
Per (phage encoded resistance) Antisense RNA |
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Briefly describe phage resistance in lytic cycle |
Restruction modification (R/M) -> Abortive infection -> Adsorption interference |
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Importance of bacteriophges |
Early mode for molecular genetics and biology Therapy-antibiotic resistance Important component of modern biotechnology |
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Advantages of bacteriophages |
Very specific- affects targeted bacterium only Chance of developing secondary infects reduced No side affects Phage able to reproduce as long as host bacteria is available Development of resistance may lead to virulence Selection of new phages can overcome resistance Production simple and relatively inexpensive |
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Advantages of antibiotics |
Can be used without knowing the ID of the bacteria |
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Disadvantage of bacteriophages |
Disease causing bacteria must be identified before therapy |
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Disadvantage of antibiotics |
Non-specific action that targets pathogen and normal flora leading to secondary infections
Multiple side effects: yeast infection, allergies , intestinal disorders Repeated administration is needed Antibiotic resistant bacteria remains pathogenic Development of new antibiotic takes years Production is expensive |
