L11, 12 - Genetics of Bacteria Flashcards
Nutrient Broth contains
rich media derived from yeast extract and casein
Minimal media contains
Na+, K+, Mg2+, Ca2+, Fe2+, NH4+, Cl-, phosphate buffer ph7, glucose as carbon source
What is Prototroph?
a bacteria which can grow on minimal media and synthesis all necessary amino acids, vitamins and lipids
What is Auxotroph?
When a bacteria will grow only if an extra ingredient is added to minimal media e.g. an amino acid
Lag phase
initial period where bacteria adapt to media
Exponential or Log phase
period of rapid growth where the bacteria are dividing in a fixed time interval called the doubling time
Stationary phase
Cells stop dividing due to limited nutrients
Escherichia coli
has a circular double stranded DNA genome which is 4,600 kilo bases pairs (kb)
What are the 3 methods of genetic exchange in bacteria vis horizontal gene transfer?
Conjugation, transduction and Transformation
What is Conjugation?
- Transfer of plasmid
- Transfer of the bacterial genome when a plasmid capable of conjugation is integrated into the bacterial genome
What is Transduction?
- bacteriophage can package a DNA fragment from the bacterial genome and transfer it to another bacterial cell
What is Transformation?
- uptake of DNA fragments by the bacteria from the environment
To enhance the level of competency in a population of E.coli cells, they can be grown in…
rich liquid culture, harvested in the exponential growth phase and treated with a SALT SOLUTION
Linear pieces of DNA need to integrate into the E.coli genome by …
Recombination in order to survive
What happen to the linear pieces of DNA that did not integrate with the E.coli genome?
They cannot survive and will be digested by DNase activity to single nucleotides
What does a bacteriophage composed of?
An icosahedral head, hollow protein sheath and sometimes a set of tail fibres
Types of bacteriophage
T4 phage and Lamda phage
What are the 2 types of Transduction by bacteriophage?
Generalised transduction and specialised transduction
What is generalised transduction?
it is the transfer of any bacterial genes, is carried out by bacteriophages that cannot distinguish between phage and bacterial DNA when assembling virus particles
What is specialised transduction?
it is carried out only by temperate phages whose genome integrates into the bacterial genome and the inly genes transferred are those close to the integration site
Size of F plasmid
100 kb
The feature of F plasmid
1) approximately 30 transfer (tra) genes
2) an origin of replication (oriV)
3) an origin of transfer (oriT)
4) Three insertion sequences (IS)
Features of R plasmids
1) have tra genes so can conjugate between different species of bacteria
2) carry genes that confer multiple antibiotic resistance
3) large 100kb
Features of ColEl plasmids
1) small (6.6 kb) and does not carry tra gene cluster so CANNOT move by itself between different bacteria
2) carries ColEl gene that produces a protein colicin which is excreted from the cell and toxic to other bacteria (not the host)
