Sources of genetic mutation in bacteria:
- Mutations
2. Horizontal gene transfer
2 major types of Mutations
Base substitution mutations
AAC-CGT-GGA –> AAT-CGT-GGA
Addition/Deletion (frameshift)
AAC-CGT-GGA –> AAT-CCG-TGG-A
Three possible outcomes for base substitution mutations
- Silent: nothing happens
- Missense: codes for diff. amino acid
- Nonsense: codes for a STOP codon
Spontaneous mutations
- occur during normal cell processes
- random and infrequent, but at characteristic rates
Reversion
A mutation will change bah luck into its original non-mutated state.
Point mutations
When only one base pair is changed
Induced mutagens
When a mutagen damages or changes DNA increasing the mutation rate.
Chemical mutagens
Some chemicals can modify DNA or resemble DNA bases, often resulting in base pairing mistakes.
ROS
Reactive oxygen species that can damage DNA.
Base analogs
Structurally resemble nucleobases , can be mistakenly used in place of nucleobases.
Intercalating agents.
- “Insert” between adjacent base pairs in the DNA strand.
- Increase frequency of frame shift mutations
Ex: ethidium bromide chloroquine
2 types of radiation used as mutagens:
- Ultraviolet mutation
2. X-Ray mutation
Ultraviolet mutations
Causes covalent bonds to form between adjacent thymine molecules causing a thymine dimer.
Lethal
X-Ray mutations
Cause breaks in the DNA backbone and alters bases.
Lethal
Proofreading
DNA polymerase can back up and remove nucleotide that is not correctly hydrogen bonded.
Mismatch repair
Fixes everything missed by DNA polymerase proofreading.
SOS repair
- Last effort to repair extensive DNA damage.
- Increases mutation rate itself.
Generalized transduction
When a bacteriophage injects the bacterial cell and makes more phages it accidentally takes up a peace of the host DNA and transfer it to the next bacterial cell.
