Microbial Genetics Flashcards
What is the central dogma?
The central dogma of molecular biology is the process of how DNA turns to RNA and to a protein. DNA is replicated, then it is transcribed into RNA and translated into a protein. Replication is when DNA gets copied into DNA. During transcription, DNA is converted into RNA. Finally, translation is when RNA is converted into a protein.
What is a mutation?
when there is a change in the DNA sequence.
What is a point mutation?
Substitution of a single base.
What is a silent mutation?
a change in the DNA sequence but there is no change in the amino acid sequence
- does not have an effect on the structure of the protein
What is a missense mutation?
one amino acid is changed into a different amino acid
- results in the change of the meaning of the codon
- the effects of this mutation can be significant depending on the location of the changed amino acid.
What is a nonsense mutation?
a change in the base pair of a DNA sequence causes a change in an amino acid into a stop codon
- this type of mutation results in the formation of proteins that are shorter and nonfunctional.
What is a frameshift mutation?
a shift in the reading frame is caused by the addition or removal of one or two bases. If the number of nucleotides is not a multiple of three, it can cause every single amino acid that comes after to change. This type of mutation can be extremely problematic and have a dramatic effect on the protein.
How does positive selection work?
only the microbe that one wants to grow can grow
What is an example of positive selection?
if one is looking for cells that are ampicillin resistant, one could grow bacteria in a tryptic soy agar with ampicillin added to it. When they are spread, only the cells that are resistant to ampicillin can grow and form colonies.
What is negative selection?
the microbe that an individual wants to grow does not grow. This type of selection is used for mutants that are not able to make their own nutrients.
What is replica plating?
used to identify mutants that cannot make their own histidine
1. a plate with sterile velvet pressed onto it is used to press down onto the plate with bacterial colonies.
2. The sterile velvet picks up the cells from bacterial colonies. These cells are then transferred to two different plates. One medium contains histidine and the other lacks histidine. The cells are pressed into each plate.
3. After the transfer, the two plates are incubated.
4. Finally, after incubation, the growth or absence of growth on the plates are compared. In this step, one looks for the microbe that can no longer grow on the selected media.
How does the Ames test work?
used to detect whether a chemical is a mutagen
- For example, a salmonella strain can be used as a test strain to find if a chemical is a possible mutagen that causes the formation of mutants that go from his- to his+. To begin, a salmonella strain that requires histidine is taken and plated on a medium that lacks histidine. In this medium, the only microbes that grow are those that are his+. The cells are grown and incubated. What can be seen are two his+. This is the background mutation rate. After, the possible mutagen is mixed into the tube with the salmonella strain. This is plated and incubated. If there is greater growth on the plate than the background mutation rate, it shows that the possible mutagen is causing mutations. In both tubes, rat liver extract is used to mimic liver metabolism.
What is the difference between vertical transmission and horizontal transfer/transmission?
Vertical transmission is the transfer of genetic information from parent cell to daughter cell via binary fission. Horizontal transmission is the passing of genetic material between two unrelated cells. In this type of transfer, DNA is transferred unidirectionally from a donor cell to a recipient cell. There are three mechanisms of horizontal transfer, transformation, transduction, and conjugation.
What is transformation?
when a cell picks up DNA found in its environment. The DNA comes from other cells that have lysed and released their contents into the environment.
What is Griffith’s experiment?
Griffith noticed that there were different strains of streptococcus pneumoniae, a rough strain, and a smooth strain. The rough strain contained colonies that appeared rough while the smooth strain contained a capsule that made it smooth. When he injected the rough strain in a mouse, the mouse lived, signifying the strain was nonvirulent. However, when he injected a smooth strain into a mouse, the mouse died, meaning the strain was virulent. In his experiment, he conducted three tests to see whether a capsule was causing virulence. In the first test, he took a smooth strain, heat-killed it, and injected it into a mouse. The mouse lived. In the second test, Griffith took a rough strain and the heat-killed smooth strain and mixed them together. He injected this mixture into the mouse, and the mouse died. In the third test, he reinjected the virulent strain from the dead mouse in the second test and the mouse died. Griffith’s experiment showed that dead smooth cells were able to transfer genetic material to the living rough cells. The rough cells picked up genetic material from the heat-killed smooth cells. They used the genetic material from the heat-killed smooth cells and developed capsules. His experiment demonstrated transformation.
