L10: Genetics of Bacteria Flashcards
Bacteria is grown in…
Liquid medium
Agar plate
2 types of media
1) Nutrient broth
2) Minimal media
3 bacterial growth phases
1) Lag phase
2) Exponential (log) phase
3) Stationary phase
Which phase of bacterial growth is characterised by rapid cell division?
Lag Phase
What happens during the exponential/log phase?
Period of rapid growth where bacteria are dividing in a fixed time interval (doubling time)
What happens during the stationary phase?
Cells stop dividing due to limited nutrients
How does wild type E. coli grow on minimal media?
By synthesizing all necessary components from minimal media
3 methods of genetic (DNA) exchange between bacteria
1) Transformation
2) Transduction
3) Conjugation
Describe transformation in bacterial DNA exchange
uptake of DNA fragments by bacteria from the environment
Describe transduction in bacterial DNA exchange
Gene transfer via bacteriophages
Describe conjugation in bacterial DNA exchange
Direct transfer of DNA via cell-to-cell contact/conjugation pilus
Define natural competency
Specific physiological state in which prokaryotes are able to take up genetic material
2 features of natural competency in transformation in bacterial DNA
1) only a small fraction of bacterial cells naturally take up DNA
2) competency is only induced in a lab using CaCl2 treatment
How does the environment influence the competency of bacteria for transformation?
The bacterial growth state
Process of transforming plasmid into competent E.coli cells
- Incubate competent cell
- Heat shock at 47 degrees for 30s to encourage plasmid to enter cell
- Place back in ice
- Place on selective agar media plate
- Incubate for 24 hrs at 37 degrees
Structure difference between T4 phage & lambda phage
T4 phage contains tail fibers, base plate
Lambda phage doesnt have tail fibers, base plate
What is the significance of the lag phase in bacterial growth?
Bacteria are adapting to the new media
What happenns when generalised transduction occur?
1) Host bacteria with 2 genes
2) Phage fuses with enzyme that chops genome into bits
3) A virus picks up a piece of host genomic DNA that is the same size as its own and transports it to another cell
4) virus infects cell injecting bacterial chromosme into the cell
5) digested by cellular digestases to become a transduced bacterium
How does the presence of introns differ between bacterial and eukaryotic genomes?
Bacterial genomes typically lack introns
What are the four phases of bacterial growth in culture?
Lag phase, exponential phase, stationary phase, death phase
What is the significance of homologous recombination in bacterial genetics?
To integrate transferred DNA into the chromosome
What is the significance of studying the complete DNA sequence of E. coli?
It provides insights into fundamental genetic principles
What is the importance of operons in bacterial genomes?
Coordinating the expression of related genes
What happens to arg- E. coli when grown on minimal media without added arginine?
will not grow
What features characterize the F plasmid in E. coli?
Transfer genes, oriV, oriT, and IS
What happens to the recipient cell during conjugation with an F+ cell?
Becomes an F+ cell
Describe the discovery of conjugation using Y-24 & Y-10
Individual growth of Y-24 & Y-10 grown on complete medium showed no growth
Mixed Y-24 & Y-10 showed colony growth
What does conjugation require the physical contact between?
Donor (F+) & Recipient (F-) cells
How is genetic information transferred through in conjugation?
hollow tube made of proteins (conjugation pilus/conjugation tube/sex pilus)
What does F plasmid carry?
Genes which enable genetic exchange by conjugation
Features of the F plasmid
1) Approx 30 transfer (tra) gene
2) An origin of replication (oriV)
3) An origin of transfer (oriT)
4) 3 insertion sequences (IS)
Mechanism of the F plasmid by conjugation
1) F+ cell has a conjugation pilus that attaches to the F- cell
2) One strand of F plasmid (T strand) is transferred into the F- cell
3) Single strand nick produced at oriT
4) Both cells become F+
When does the F plasmid integrate?
When a homologous recombination event occurs between 1 of its IS sequences & 1 of the several IS sequences
What distinguishes Hfr strains from F+ strains in E. coli?
Hfr strains have the F plasmid integrated
How does the lytic cycle of T4 phage affect bacterial cells?
It causes bacterial cell lysis
