Brewer - Bacterial Genetics Flashcards
What is the structure of bacterial DNA
Circular
How does genome size reflect life style
The more genes something has the more capabilities it has. For instance E. coli has many more genes so it has the ability to live on just glucose. Mycoplasma on the other hand has a lot less genes and therefore needs a whole lot more to be present in the media.
Replicons
Site for initiation of DNA synthesis within bacterial chromosomes and plasmids.
How do you detect a plasmid?
You lose cells so that the plasmid espaces, but the chromosome stays inside of the cell. You then seperate the plasmids based on size on a gel electrophoresis. You ad ethidium bromide to make it fluoresce.
- If all of the brightness is concentrated in one area then it is one plasmid. If it is in different areas then it is many different plasmids.
What is a bacteriophage?
Viruses that inject their genomes into a bacterial cell and uses its machinery for its reproduction.
What are the two types of bacteriophage?
Virulent - bacteriophages release progeny by lysis of cells
Temperate - bacteriophages insert genomes into bacterial chromosomes and replicate with it.
Provirus/prophage
Integrated viral genome into the bacterial chromosome that we see in temperate bacteriophages
Insertion sequence
Can move from one location of DNA to another.
- the only gene that is has is for transposase, which is the enzyme that allows it to move from one spot to another.
- have an inverted repeat on both ends
Transposons
Resemble insertion sequences but contain other genes other than just transposase gene. Therefore it can move genes like the antibiotic-resistance genes.
Pathogenicity Islands
Are basically just very large Transposons. Can contain 50-100 gees. May contain a whole set of virulence genes for a particular organism.
Two modes of transposition
Cut and paste
Replicative
How does replicative transposition work?
It fuses donor and recipient molecules and then resolves them.
3 mechanisms of DNA transfer between bacterial cells
Transformation
Conjugation
Transduction
Transformation
One cell will pick up DNA fragments from a dying or lysed cell.
COnjugation
Plasmid DNA from a donor cell is transferred to a recipient through a conjugation bridge/pilli.
How is it that chromosomal DNA can be transferred through conjugation?
The F plasmid can be incorporated into the chromosome and the a conjugation bridge will form. The chromosome then acts just like a plasmid. The issue though is that these bridges are transient and break shortly so only a smart part of the chromosomal DNA will make it to the recipient cell.
Transduction
- When a virus enters a cell, it can incorporate bacterial DNA into the progeny, so when. The cell lysis and the virus spreads, it could be spreading bacterial DNA
- The virus DNA can also have a small part of bacterial DNA in it.
Merozygote
Complete bacterial chromosome + partial DNA fragment from donor.
Phase variations
When microbes continue to create new variants of the antigen to escape the immune system.
- with each wave of antibiotics, there can be one microbe that alters its antigen and stays alive to proliferate the net generation.
Three mechanisms of phase variation
Inversion of a segment of DNA
Recombination between expressed and silent genes
Shuttering by polymerase during copying of a repeat
How does salmonella do phase variation?
It has two genes for its flagella, H1 and H2. Only one is expressed at a given time.
- The enzyme, hin, recognizes two inverted repeats and then inverts the DNA between the repeats.
How does phase variation happen in Neisseria?
There is recombination betwen the silent copy and expressed copy of the piling genes so that a mosaic is created with alternating silent, expressed, etc.
Phase variation in Neisseria outer membrane protein, PII
There is a variation in the number of CTCTT repeats. If there is a multiple of 3 CTCTT repeats then PII is made, otherwise it is not.
