Microbiology - Lecture Thirty Four : Microbial Genetics
6 important questions on Microbiology - Lecture Thirty Four : Microbial Genetics
What are the properties of bacterial genome ?
- Single circular chromosome
- No nuclear membrane
- Nucleoid : defined, non-membrane bound region that chromosome occupies within cell
- Plasmids : smaller, self-replicating, circular DNA found in cytosol (separate to the chromosome)
What are the differences between vertical and horizontal gene transfer ?
- Gene transferred onto the next generation of daughter cells
- E.g parent --> offspring
- Genes transferred onto the same generation of cells
- Recipient cell can be of different species to donor
- Main mechanism of transferring genes to maintain virulence
- E.g one organism --> another living organism
What are the 4 strategies that generate genetic diversity in bacteria ?
- Mutations
- Transformation
- Transduction
- Conjugation
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Explain the "Transformation" strategy that generate diversity in bacteria ?
- Occurs when recipient cell takes up DNA fragments from the environment or surroundings
- This DNA is from nearby dead organisms)
- Competency = cell’s ability to take up DNA from their environment
Explain the "Transduction" strategy that generate genetic diversity in bacteria ?
- Transfer of DNA via replicating virus (bacteriophage)
- Occurs as replicating bacteriophage may accidentally incorporate some of the host cell’s DNA into its own viral genome
- Important tool for horizontal gene transfer in gram +ve bacteria (as their cell capsule is very impenetrable)
- Donor cell dies, as the the replicating bacteriophage lyse the cell in order to infect other bacterial hosts
Explain the "Conjugation" strategy that generate genetic diversity in bacteria ?
- Donor cell stays alive
- Requires cell-cell contact
- 1 single stranded DNA from the donor plasmid is transferred via a sex pili (thin, fibrous protein tube) to the recipient cell
- The recipient cell then replicates the donor DNA strand : double stranded donor DNA plasmid
- Often a process used to transfer antibiotic resistant genes
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