Bacterial Genetics Flashcards
What is a spontaneous mutation?
A mistake during DNA replication can substitute one base for a different base
What can a spontaneous mutation involve?
Can change a single amino acid, or add a stop codon and inactivate the whole protein
What does removal or addition of a nucleotide change?
The translational reading frame
Is it better to change one nucleotide, or a group of 3?
A shift or change of a group of 3 nucleotides has a less damaging effect on the strand.
In which 3 ways can a mutation be induced?
UV or X-ray radiation, or chemicals that alter DNA
What is the effect of vertical gene transfer on progeny?
All the progeny of that bacteria have the new DNA sequence
At what rate do spontaneous mutations occur?
Occurs between 1 in 104 and 1 in 1012 in a given gene when a cell divides
What are the names of the two types of “directional” gene transfer that contribute to bacterial diversity?
Horizontal and vertical.
What are the 3 types of Horizontal Gene Transfer?
- Transformation
- Transduction
- Conjugation
What is Transformation?
The transfer of genetic material from transfer of naked DNA
What is Transduction?
The transfer of genetic material from one bacterium to another by a bacteriophage
What is Conjugation?
The transfer of genetic material from one bacterium to another by means of conjugation pili
What are the 3 steps of Transformation?
- Cells rupture during the stationary and death phase (The chromosome breaks into small pieces)
- Recipient cell picks up piece of the naked DNA
- The naked DNA is integrated onto the recipient chromosome
What condition is required for natural transformation to occur?
Natural transformation occurs when bacterial cells are “competent”
When is bacterial competence?
Competence is a condition in which bacterial cells are capable of taking up and integrating larger fragments of DNA
When does bacterial competence occur?
During the late log, early stationary phase
How can bacterial competence be induced?
By treating bacteria with certain chemicals/electric current.
What is is a mis-packaging of DNA during viral replication, with regards to horozontal gene transfer, called?
Transduction
What are the steps of Transduction?
- Bacterial DNA that is transferred from donor to recipient via a bacterial virus (bacteriophage)
- The mis-packaged phage infects a new bacterial cell and inserts the donor DNA into the recipient cell
- The donor DNA is integrated and mis-matched pairs are repaired
What are plasmids?
Extrachromosomal circular DNA found in bacteria (as well as Archaea and Eucarya)
How many plasmids are found in each bacterium?
From 1-500
Plasmids are readily transferred by . . .
Conjugation
Give an example to illustrate that Plasmids are useful but not essential.
R Plasmids that confer resistance to many different antimicrobial medications
Genes that code for resistance to three antimicrobials are called what?
Resistance
Genes that code for transfer of the plasmid from bacteria to bacteria are what?
Resistance Transfer Factor
What is Conjugation mediated by?
RTF (Resistance Transfer Factor) region of plasmid
How do bacteria achieve direct contact between cells during Conjugation?
Via the sex or F pilus
What is the plasmid that codes for a pilus on the donor cell?
The fertility factor or “F factor,” which is designated F+
What is the designation of the Recipient cell, which does not carry a plasmid?
F-
What are the 4 steps of conjugation?
- Sex pilus of donor cell recognizes and binds specific receptor on recipient cell
- Cells are pulled together
- DNA is transferred (starting at origin of transfer region) to recipient [Single strand of DNA transferred, single strand left behind]
- Synthesis of functional (double-stranded) plasmid in both donor and recipient
What happens to the recipient cell after conjugation?
After the plasmid is transferred, the F- cell becomes F+
What happens to the donor cell after conjugation?
Donor survives (as apposed to transformation and transduction)
