Bacterial Genetics Flashcards
Describe the General Secretion Pathway (post-translational).
- The chaperone SecB takes the protein to the docking protein SecA.
- ATP is hydrolyzed; Protein pushed through translocon (SecYEG).
Describe the Signal Recognition Pathway (co-translational).
Energy required (GTP); Target proteins to CM
- Signal recognition particle binds signal sequence
- Protein is pushed into translocon (SecYEG)
Are bacteria haploid or diploid?
They are haploid
How do bacteria acquire genetic variation?
Random mutations and Acquisition of new DNA by horizontal gene transfer.
What are types of mutagens?
Chemical, Radiation and viruses.
What are the types of chemical mutagens?
Nucleotide analogues, Frameshift mutagens (Dna intercalating agents)
What are the types of DNA repair?
Direct DNA repair, Excision repair, Post-replication repair, SOS response, and Error-prone repair.
What does Direct DNA repair fix?
A single damaged nucleotide.
What does Excision repair entail?
A segment of damaged DNA is removed and replaced.
What does post replication repair do?
Involves recombination with homologous sequences.
What is the SOS response?
An inducible DNA repair system.
Describe error prone DNA repair.
It replaces accuracy with speed.
What are the 3 types of genetic exchange in bacteria?
Transformation, Transduction and Conjugation.
What is transformation?
The uptake of naked DNA from the environment; Need competent recipient cell.
What are the steps to transformation?
- Binding of exogenous DNA to cell surface.
- Uptake of donor DNA into cells
- Recombination with the recipient cell genome.
What is Transduction?
Transfer of DNA from donor to recipient cell via bacteriophage. Bacteriophages are either lytic or lysogenic.
What are the 2 types of transduction?
Generalized and Specialized transduction.
Describe Generalized Transduction.
Lytic phage destroys host cell DNA. Small fragments of host cell DNA can be packaged into phage heads as new phage particles are formed. These pieces of bacterial DNA can be injected into new host cells when the virus infects. This is a low frequency transduction.
Describe Specialized Transduction.
Lysogenic phage infects host bacterial cell. Prophase integrated in host cell genome. When prophage excises to produce new virions, it could pick up pieces of host cell chromosome. These genes co-integrate into the chromosome of a new recipient cell along with phage genome.
Describe the transduction frequencies in specialized transduction.
The initial event of picking up bacterial DNA occurs at low frequency. Once a phage has picked up the DNA, all progeny phage will carry it as well and introduce it into new hosts at High frequency.
Describe bacterial conjugation.
Plasmid mediated transfer of DNA from donor to recipient cell by direct contact; Governed by plasmid genes.
Describe standard conjugation.
Conjugation between F+ and F- cells. Involves replicative transfer of DNA. One strand directs synthesis of its complement within donor cell. Other strand is transferred to the recipient cell, where its complementary strand is synthesized. Plasmid recircularizes and replicates independently in the recipient cell. Results in high frequency transfer of plasmid but not of host chromosomal genes. Both cells are F+
Describe conjugation involving an Hfr donor
The F plasmid is integrated into the host chromosome. Incomplete transfer of F plasmid sequence leaves recipient cell F-; Donor remains Hfr.
What are the fates of transferred DNA?
- Degraded by nucleases.
- Stabilization by circularization (plasmid)
- Integration into host chromosome
