Prokaryotes Flashcards
(37 cards)
What is nutrient broth?
Rich media derived from yeast extract and casein.
What is minimal media?
The basic synthetic medium for bacterial growth without nutrient supplements
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.
How quickly can E. coli replicate?
They can divide once every 20 minutes.
What are the phases to bacterial growth?
Lag phase - initial period where bacteria adapt to media.
Log phase (Exponential)- period of rapid growth where bacteria are dividing in a fixed time interval called the doubling time.
Stationary phase (Plateau)- Cells stop dividing due to limited nutrients.
What is the purpose of streaking bacteria on an agar plate?
You streak the bacteria on the agar plate so that you get a single bacteria on its own. This bacteria will produce a colony after incubation and all the progeny in the plate should be genetically identical.
What are defining characteristics of prokaryotes?
The lack nuclear membranes and true chromosomes
They are haploid, and so have only one copy of each gene
Unicellular does not apply as yeast cells are unicellular eukaryotes
How many base pairs and genes does E. coli have?
4,600 kilobases
4288 protein coding genes
7 ribosomal RNA operons
86 transfer RNA genes
What does lac- mean?
Bacteria cannot utilise lactose as a carbon source.
What does arg- mean?
The bacteria needs arginine added as a supplement to minimal medium because the bacteria itself cannot make its own arginine
What are the three methods of genetic exchange in bacteria?
Conjugation- transfer of plasmids
Transduction- Packaged DNA fragments from bacteria genome are transferred to another bacteria
Transformation- DNA fragments are taken up by the bacteria from the environment
What is transformation of genetic information for bacteria?
Bacteria take up linear pieces of double stranded DNA from dead bacteria in their environment.
DNA will bind to receptor site, one of the strands is degraded as it enters the cell. The transforming strand pairs with the homologous region of the recipient chromosome.
What chemical competency have to do with transformation in bacteria?
Very few bacteria are capable of taking up DNA by transformation at any one time - their competency varies depends on their state of growth.
Maximum level of competency is during exponential growth.
What is a bacteriophage?
Viruses that infect bacteria
What is the lytic phage life cycle?
The process that leads to lysis of the host cell
- Attachment of the (bacterio)phage to the host cell
- Injection of the phage chromosome into the host
- Replication of the phage DNA
- Transcription and translation of the phage genes (which makes the heads, sheaths etc. of the phage)
- Packaging of the phage chromosomes into the phage heads
- Lysis of the host cell and release of the progeny phage particles
What are the two types of transduction?
Generalized transduction- The transfer of any bacterial genes, is carried out by bacteriophages that cannot distinguish between phage and bacterial DNA when assembling virus particles.
Specialized transduction- Carried out only by temperate phages whose genome integrates into the bacterial genome and the only genes transferred are those close to the integration site.
How are plasmids transferred via conjugation?
The donor cell assembles a conjugation pilus to contact the recipient cell.
The relaxosome complex bind the factor at the ori and cleaves the ‘T strand’ of the DNA.
The relaxosome partially degrades, leaving relaxase bound at the 5’ end of the T strand. Rolling circle DNA replication begins in the donor.
The exporter moves the relaxase-T strand complex into the recipient cell. Rolling circle replication in the donor spools the T strand to the recipient, where it is a template for DNA replication.
The completion of replication in both cells leaves the donor unchanged and converts the recipient cell to the donor state.
Discovery of conjugation
Lederberg and Tatum discovered
They took two cultures of e coli.
Each strain had different genotypes, but neither could grow on minimal media.
If you mixed the strins together they would allow a colony to grow on minimal media.
What are IS sequences?
IS sequences allow F plasmids to integrate with the chromosome.
There are IS sequences on the plasmid and on the chromosome.
What is the F plasmid?
The fertility plasmid.
F plasmid carries genes which enable genetic exchange by conjugation.
It contains 100 kb which include tra genes Origin of replications (oriV) Origin of transfer (oriT) 3 Insertion sequences (IS)
How long does it take for the F plasmid to transfer between to F- cells?
2 mins
Mapping genes on E. coli chromosome
There is a Hfr strain and a F-strain.
The Hfr strain has all of the wild type genes but is streptomycin sensitive, whereas the F- cell has none of the wild type genes, but is streptomycin resistant
These strains are mixed together (time 0)
Every 5 minutes for about 25 minutes, take out a sample of the cells, vortexing them to break cell-to-cell contact and plated onto the agar plates with different selective media (lac+, gal+, aziR and tonR), all of which contain streptomycin.
Plot the frequency of Hfr genetics against the time. The lower the time, the closer the gene is to the oriT.
What are R plasmids?
Resistance plasmids.
They carry genes that confer antibiotic resistance.
They have the tra genes so can conjugate between different species of bacteria.
