PMB: Bacteria Genetics 4 Flashcards
Describe bacteria genetics
- Have a relatively small genome
- Rarely (if at all) use introns (non-coding regions)
- Very little redundant DNA
- Able to respond quickly to enviromental changes
- Rapidl changes in gene expression levels (both upregulation and downregulation)
It is important for bacteria gene expression to be regularlated properly.
How is this done?
- Achieved by the action of σ-factor directing RNA polymerase promoter recognition
- cAMP is also important
What are operons?
In order for genes with similar roles, or which interact with each other, to work together the are often controlled at the same time.
For example, a metabolic process often requires several genes working together. These genes are often located close together due to them carrying out related activities. These related genes are often transcribed together and when this happens theya re referred to as operons.
How can you test for mutant colonies?
Replica plates can be achieved relatively easily by the method shown above. Colonies grow on the original plate. Place some sort of cloth (cheesecloth is a good choice) over a block of wood which is almost the same size as the plate with the agar. Gently touch the cloth into the plate and then gently touch it on to another plate. This second plate should be slightly different from the first plate – although remember to keep the first plate. For example, it may lack a specific nutrient (e.g. one of the amino acids). Assuming this is a nutrient which the organism can normally make, then colonies should grow on the new plate. However, there may be a few mutant colonies, where this gene no longer works. By comparing the new plate, and looking for colonies on the original which are not on the new plate, this serves as an indication for mutant colonies. By returning to the original plate, these can be isolated and studied in more detail.
Describe the Ames test and what it is used for
Use bacteria to check for mutagens
What are the genetic components of bacteria? Where is genetic informaiton kept?
- Bacteria contian one chromosone but can contain other forms of DNA
- Most essential genes are located on the chromosome (single copy)
- Non-essential/ luxary genes are located in plasmids (multiple copy)
- Can contain one, many and different plasmids
What are examples of genes in the chromosomes and genes in the plasmids?
- Chromosomes:
- House keeping genes - genes essential to every day activities
- Genes - structural components and metabolism
- Single copy only
- Plamids
- Luxary genes
- genes - antibiotic resistance, virulence, conjugation
- Generally genes which are not necessary for the survival of the bacterium under “normal” conditions
- often multiple copies of plamisds
Why can antibiotic resistance be useful but also a disadvantage?
- AB resistance protectes against antibiotics. If they are exposed to AB without it they will be killed
- Without AB resistance replication/ multiply at a much faster rate (2%)
What are other examples of important pieces of bacterial DNA?
- Transposons and insertion sequences
- These can move from onr position to another in the genome
- If they insert in the middle of a gene it will often lose its function
What methods cause bacteria to aquire new DNA from elsewhere?
- Transformation
- Transduction
- Conjugation
What is the evidnece behind transformaiton?
The work to demonstrate the existence of transformation as a phenomenon was a performed even before DNA had been categorically accepted as the molecule of inheritance. Therefore, if you look at the paper on the link, remember that point.
In this work there are two different strains of Salmonella used; smooth (S) which is lethal to mice and rough (R) which are non-lethal. If the S strain is heat-treated (i.e. killed) then it is no longer able to infect the mice and kill them. However if live R cells and dead S cells were mixed and allowed to infect the mice, some mice died. When the dead mice were investigated they were found to contain S cells. Since dead bacteria are not going to come back to life, it was concluded that the R strain acquired some DNA from the S strains which had burst open. In other words the R strain obtained some S strain DNA by the process of transformation.
What is a competent cell?
How do these cells come about?
A cell which can be transformed
Some cells are naturally competnet, others it is possible to artifically make them competent
How do you make a cell competent?
Using an appropriate growth medium can make cells competent.
At the correct stage of development they can have DNA introduced
Changes are present in bacterial cell wall - this is required
What happens to transformed DNA?
- Often transformed DNA will be destroyed by nucleases in the bacterial cell
- Some pieces of DNA will be integrated into the genome (catalysed by recA)
- If incorporated this alters the genome
What does conjugation do?
Transfers a plasmid from one bacteriu,to another
