How do new Genotypes occur in microbes?
-heritable change in DNA
-SOURCE of new genotypes
-DNA exchange between cells
-SPREAD of new genotypes
What is wildtype and mutant?
Wild type = normal
What is a phenotype mutation?
Change in observable properties of the organism
What are the different types of mutations?
-single nucleotide change
Frame Shift Mutations
-Insertion OR Deletion of nucleotides
-Also known as Indel
-lengthened or shortened
What are the types of point mutations?
-Purine to Purine A⇔G
-Pyrimidine to Pyrimidine C⇔T
-Purine to Pyrimidine A/G⇔C/T
-Pyrimidine to Purine C/T⇔AG
-change from mutant to wild type
What are the types of effects of mutations?
-mutation results in same amino acid
-mutation inserts premature stop codon
-Mutation causes different amino acid
What are the types of Frame Shift Mutations?
Both shift the reading frame by adding/removing nucleotides
What are the sources of mutations?
-due to errors in DNA replication
-DNA Polymerase not 100% accurate
-Due to external agents, ie mutagens
How often do spontaneous mutations occur?
Lethal mutations balanced by adaptive mutations
Vriruses have a higher frequency of mutations
What are the types of mutagens?
Physical, Chemical, and Biological
What are the types of physical mutagens?
-breaks DNA strand
What are the types of chemical mutagens?
Nucleotide base analogs
-resemble nucleotide but not, used by DNA polymerase by mistake
-causes point mutation
-change structure of nucleotides
-cause point mutation
-chemical inserted between DNA base pairs
-cause frameshift mutation
Sometimes mutagenisis causes carcinogenesis. How do we test for chemicals that mutagenic?
The Ames Test
-start with bacteria we've mutated with single substitution
-place in low nutrient media
-if mutagenic then we will see growth b/c some of the mutations caused by mutagen will be reversions and the mutated bacteria will go back to wild type
When using the Ames test, how can you tell if you have spontaneous or induced mutations from the potential mutagen?
-Few colonies b/c non-mutagen
-Many colonies b/c mutagen
How does gene transfer occur and what are the possible outcomes?
Horizontal Gene transfer between source and receiver
1. Rejected - degraded by recipient cell
2. Accepted - replicates independently, eg plasmid
3. Accepted - inserted in recipient chromosome
How is DNA inserted into the chromosome?
Homologous recombination between Donor DNA and Recipient DNA
-Homologous = similar DNA sequences
-crossing over like in meiosis
What are the different types of gene transfer?
-naked DNA uptake from the environment
-virus-mediated, virus injects bacterial DNA into host cell
-direct passage of DNA from one cell to antoher
How does transformation occur?
Donor cells lyse → DNA in environment
-DNA outside of cell = ''naked'' DNA
Recipient cells take up nake DNA
What kinds of cells can undergo transformation gene transfer?
Competent cells able to take up naked DNA fragments
-not all bacterial cells are competent
How does bacteria choose the right naked DNA to uptake from environment for transformation gene transfer?
-quorum sensing causes bacteria to take up DNA
-must be present to uptake DNA
-recognition sequence in DNA must be present to be taken up
What is transduction?
Form of gene transfer where virus transfers DNA between cells
-viruses that infect bacteria=bacteriophage
-bacteriophages inject their genome into host cells
-normal phage destroys host cells
-in transduction the bacteriophage injects it's genome that contains some of last bacterial host into new host
-New host cell intact w/ new DNA
What is conjugation?
Form of gene transfer that involves cell-to-cell contact
-direct gene transfer
-plasmids and chromosomes are exchanged
What is machinery is involved in conjugation?
-genes for replication and transfer functions
-contacts recipient cell
-retracts to bring cells together
What does the F plasmid do?
single strand of plasmid enters recipient cell and synthesizes complementary stran
-gives recipient cell ability to conduct horizontal gene transfer
-F plasmid integrates into chromosome via recombination
What is mobile DNA?
Type of mutagenesis
-has transposable elements
-genes that move within or between DNA molecules
-can't replicate independently
-the movement of transposable elements
What are the types of transposable elements?
1. Insertion sequences (IS)
-shorter DNA segments
-single gene, transposase, an enzyme that cuts out segment of DNA and puts somewhere else
-longer DNA segments
-eg. transposase+antibiotic resistance
What are the types of transposition?
-transposon moved to new DNA molecule
-absent from donor DNA, present in recipient DNA
-transposon is replicated AND moved
-present in donor and recipient DNA
What is a biological mutagen?
When transposition causes mutation
-insertion into a gene which disrupts its function
-transposition used to create bacterial mutants
-disrupting the gene to study its function
-# of transposons related to how fast you involve