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26 Cards in this Set
- Front
- Back
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What 3 components make up the bacterial genome? |
Chromosomal DNA Plasmid DNA Transposons |
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How is chromosomal DNA described, and where is it found? |
Principal DNA, found in the nuclear region |
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How many chromosomes and copies are involved in the chromosomal DNA? |
1 chromosome 1 copy |
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What is the structure of chromosomal DNA? |
Circular/double stranded Supercoiled |
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What shape is the plasmid DNA and how does it replicate? |
Circular - independent replication |
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How is plasmid DNA described? |
Auxiliary (helper) but addiction mechanisms exist |
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Name the 5 different kinds of plasmid. |
R - resistance V - Virulence Col - Colicin F - Fertility D - Degradative |
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How many types and copies of plasmid DNA are present in each cell? |
More than one type, each with more than 100 copies. |
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What is particular to transposons? |
Most primitive form of self-replicating gene. |
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What are the two main components of transposons? |
Inverted repeats (different in different transposons) Tranposase |
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What effect does genetic bacterial variation have? |
Virulence Resistance to host Resistance to treatment |
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What are the five main mechanisms of genetic variation? |
1. Use of multiple genes, where only one of multiple vaguely similar genes can be used. For example, a gene encoding surface antigens can be switched off and another activated, evading the host's immune response. 2. Slightly different fragments of the same gene can swap in and out of the same gene. For example, to for the gene encoding surface antigens, making it evade the host's immune response. 3. Gene can turn 180 degrees to give rise to an altered product. 4. Transposons can cause frameshift mutation or can integrate stop/start codons to alter expression. 5. Spontaneous mutations can occur. |
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Name the 2 types of spontaneous mutation and what they entail. |
Point mutation - 1 base change alters 1 amino acid. Frameshift mutations - 1 to 100s of base pairs added or deleted. |
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What are the three main type of recombination? |
Transformation (free DNA takeup) Transduction - generalised and specialised (bacteriophage DNA - virus infected bacteria) Conjugation (cell-cell contact) |
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How does transformation occur? |
Bacterial cell dies, releasing its DNA. Plasmid and chromosomal DNA taken up by bacteria (plasmid acts alone in cell, chromosomal integrated into chromosome) |
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Why is transformation a relatively unimportant process? |
Particular gene does not expand Extracellular DNA can be degraded Competency required for uptake Gene transfer is low and random Intracellular DNA can be degraded Homology required for chromosomal DNA |
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What is phage conversion? |
Expression of bacteriophage encoded virulence determinants (e.g. toxins, antigens) after integration into bacterial chromosome (lysogeny) |
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What is the bacteriophage genome? |
ss/dsDNA or ssRNA genome |
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What two methods of infection can bacteriophages use? |
Lytic - kills bacteria Lysogenic - Integrate into chromosome |
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Are there any uses for bacteriophages? |
Yes - disinfectant |
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What is the life cycle of lytic dsDNA bacteriophage? |
DNA enters host Host mechanisms shut down under phage control Phage replicates DNA and produces protein capsid (Progeny) Phage assemble Host cell lysis and bacteriophage particles released. |
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What is the life cycle of lysogenic dsDNA bacteriophage? |
Phage enters host Integration into chromosomal or plasmid DNA Prophage replicates Prophage excision results in phage entering lytic life cycle. |
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What is transduction?
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Error during excision of the lysogenic phage results in host DNA being picked up.
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What are the two types of transduction? |
Generalised - Host DNA excised only (integrates into host) Specialised - Phage DNA is picked up (used as template in phage replicative cycle) |
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How does conjugation occur? |
Conjugative plasmid (+ transfer operon) causes the formation of a sex pilus which isn inserted into a female bacteria and plants plasmid which goes on to replicate. |
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What makes conjugation an important process? |
Species and genus barrier can be crossed Plasmids are common No sexual preference Promiscuous male Wide host range |
