bacterial genetics Flashcards
Describe the bacterial genome
Haploid
Circular chromosome
dsDNA
some episomal elements - plasmids
Transferable DNA
Bacteriophages/viruses
What is a plasmid?
Independent small DNA molecule that replicates independently
Contains suicide genes - if plasmid lost, bacteria dies
What is the nucleoid of bacteria?
Tightly packed genome - supercoiled by DNA gyrase
- DNA binding proteins
- RNA polymerase
- RNA
- bound regulatory proteins
What is different between the transcription of bacteria and eukaryotes?
Eukaryote transcription requires splicing to remove introns
Bacteria - no introns so transcription is direct
What genes are found on a plasmid?
Replication and partition genes - required for replication and partition between cells when bacteria divide
Transfer genes - allow transfer between bacteria
Undefined bacteria
Describe replication of the bacterial genome
Via binary fission
=> clones of bacteria
How do bacteria vary their genome to evolve?
Mutation of genes
Transfer of genes
Rearrange their DNA
Delete genes
New genes inserted
What are the possible effects of mutation of bacterial genome?
Silent mutation => same amino acid
Nonsense mutation => stop codon => gene knocked out
Missense mutation => new amino acid => alters protein sequence, may affect function
What types of bacterial genome mutation are there?
Nonsense
Missense
Silent
Frame shift
What is phase variation
gene switching
Some bacteria exploit mutation to generate increased phase variation
what are the mechanisms of introduction of new DNA into and between bacteria?
Transformation
Conjugation
Transduction recombination
What are the mechanisms of movement of DNA already in bacteria
Transposition
Recombination
Describe transformation of DNA in bacteria
Uptake of naked DNA:
- degraded by nucleus
- or is recombined into genome
Describe conjugation of bacterial DNA
transfer of genetic material between bacteria through direct cell-to-cell contact
Horizontal gene transfer
similar bacteria attached by protein filament (pilus) to allow transfer
Single strand is transferred and both bacteria then produce a 2nd strand to have 2 ‘identical’ plasmids
Describe the clinical relevance of conjugation of bacterial DNA
Transfer of plasmids can move whole blocks of properties
e.g., antibiotic resistance, toxins, virulence properties
Describe transduction of bacterial DNA
Viruses that infect bacteria = bacteriophage
Virus binds to specific receptor and inject their genome to infect the bacteria
Route to transfer bacterial DNA
what are the types of transduction of bacterial DNA?
Lytic and generalised transduction
Temperate phage and specialised transduction
Describe generalised transduction - lytic bacteriophage
Bacteriophage attaches
Infection/injection of nucleic acid
Lag phase as things replicate
Lysis
=> randomly packed bacterial DNA
Describe specialised transduction - lysogenic phage
Lysogen formed
Bacterial replication with integrated prophage
Induction
Transduction
Infection with phage with bacterial DNA
Integration of new DNA
Packaged DNA related to where prophage inserted
What happens to DNA that enters bacteria?
non-specific degradation by general nucleases
Specific degradation via specific restriction endonucleases (DNA restriction)
It manages to integrate with genome (DNA recombination)
Describe homologous recombination
2 DNA sequences are the same so can intercalate their strands
Can get spliced during replication
What is directed insertion?
insertion elements have repeats which leads to homologous/directed insertions in specific sites or enzymes that direct integration at set sites
what is the role of restriction endonucleases in bacteria?
degrade DNA not made in their own cells (act on specific sites)
Describe transposition of DNA
Transposon = sequence of DNA that can move around to different positions within the genome
Encode transposases => cut out and re-insert DNA
carry accessory genes
What is the difference between gene island and gene cassettes?
Both are regions of DNA with genes conferring properties on the bacteria.
Gene island - refers to well established genes which are now part the bacteria though evolution (i.e. permanent).
Gene cassettes - elements which are more mobile and could be considered to be circulating within or between bacterial population.
What are insertion sequences?
type of transposon
Short DNA sequence that acts as a transposable element
what is the clinical relevance of bacterial mutations?
Alteration of antibiotic binding sites
Avoidance of vaccines
Alteration of metabolism
what is genetic drift?
changes over time by mutations of genomes
