Week 4 midterm 2 Flashcards
What are some features of bacteria that are useful to geneticists
- Genome simplicity
- Haploid genomes (mostly); no dominance/recessive interaction
- Short generation times
- Large progeny numbers
- Easily and inexpensively maintained and propagated
- Numerous heritable differences
Bacterial vs eukaryotic genomes
SIZE
- Small (fewer genes) vs large (more genes)
PACKING OF DNA
- DNA associated with histone proteins and supercoiled
- DNA associated with histone octamer, coiled into chromatin
LINEAR/CIRCULAR
- Circular (mostly)
- Linear
PRESENCE OF INTRONS
- Mostly no introns
- Introns within genes
CHROMOSOMES
- Often one (but not always)
- Multiple
MITOCHONDRIA
- Not present
- Present
Plasmids
- Extrachromosomal DNA
- Contain nonessential genes that are usually not necessary for life
- Can sometimes be incorporated into bacterial genome
F Plasmids
Fertility Plasmids contain genes that assist with transfer of the plasmid to another host bacterial cell
R Plasmids
Resistance plasmids contains genes that conger antibiotic resistance
What are the 3 types of horizontal/lateral gene transfer?
- Conjugation
- Transformation
- Transduction
Conjugation
Transfer of replicated DNA from a donor cell to a recipient cell
- Donor cell and recipient cell connect by conjugation pilus
- DNA- strand transfer from donor to recipient
- Crossover in recipient cell
- Exconjugant cell produced by recombination
Transformation
Uptake of DNA from the environment
- DNA fragments from donor bacteria in environment
- Recipient cell takes up donor DNA
- Crossover of donated strand with recipient chromosome
- Results in transformant cell
Transduction
Transfer of DNA form one bacterium to another by a viral vector (Bacteriophage)
1. Bacteriophage attaches to donor cell
2. Phage DNA injection leads to donor chromosome fragmentation
3. Transducing phages package donor DNA instead of phage DNA
4. Transducing phage attaches to a recipient cell
5. Donor DNA injected and recombined with the recipient chromosome
6. Transductant cell produced by recombination
- This can happen if the virus accidentally incorporates donor bacterial DNA
What is lateral gene transfer
The transfer of genetic material between individual bacteria or archaea and other organisms (can be the same species or different) - between bacteria and bacteria and eukaryotes
What percentage of the average bacterial genome is pervasive?
12%
Biased genes
Involves genes related to pathogenicity and antibiotic resistance
Conjugation with a fertility (F) plasmid
- The donor cell (F+) assembles a conjugate pilus to contact the recipient cell (F-)
- The relaxosomes complex binds the F factor at oriT and cleaves the T strand of the DNA
- The relaxosome partially degrades, leaving relaxase bound at the 5’ end of the T strand. The relaxase -T strand complex binds to a coupling factor to prepare for export. 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 (F+) unchanged and converts the recipient cell to an F+ donor state
Conversion to Hfr strain
When F plasmid becomes incorporated into the bacterial genome
- Occurs at IS element and integrated into bacterial chromosome forming Hfr chromosome
Hfr Conjugation
- Similar to gene transfer from F+ to F- except donor bacterial chromosomal genes can be transferred to the recipient
- Homologous recombination occurs between the transferred linear DNA and the circular chromosome of the recipient, generating recombinants
- Left over linear DNA degraded by enzymes
