Module 1 - long answers Flashcards
What happens when cells are infected with bacteriophage?
Resistant bacteria?
when a healthy bacteria cells becomes infected with bacteriophage the cell burst and dies
however,
In some cases bacteria are resistant to bacteriophages which causes the bacteria cells to survive
What was the hypothesis of Luria and Delbrusk experiment?
In the hypothesis, Luria and delbrusk stated that all bacteria dies when bacteriophages gets infected however the result of the experiment says otherwise
What was the outcome of Luria and Delbrusk experiment?
Some bacteria were resistant and survived these phages, they found out that being resistant to the bacteriophages was a mutation due to progeny of these bacteria also being T1 resistant themsleves
Two reasons of mutant bacteria arise?
1) presence of phages induced some of the bacteria to become resistant
2) resistance mutations arose spontaneously in the bacterial population (darwinian evolution - natural selection)
How does the process of complementation occurs in 2 different genes?
If both gene has a missing gene for the production of the protein required it undergoes the process of complementation
- In order for complementation to occurs, both gene is put in a cell where both mutants who are carrying the normal phenotype gene is combined together (only takes the normal allele) where they can complement both gene and make the proteins required for that specific phenotype where defects in the gene is ignored and we get the release of progeny phage
progeny phage appearance
these are identical to complementated 2 phages, it has the same genetic material (no difference), so its just really making up for the defected genes of the two parental phages
When does complementation occur?
Complementation occurs if the mutations are in the same gene, so if the mutations are on different gene then complementation is absent
How do we recognize mutations
By determining the DNA sequence of wild type and mutant genes
Ways in which mutation can arise
1) Spontaneously due to errors during DNA replication (i.e. DNA polymerase makes a mistake)
2) induced via mutagens
3) Arise due to transpoons
What are the mechanism for reducing spontaneous mutation?
1) DNA proofreading
2) Mismatch Repair system
Importance o DNA Proofreading
1) DNA proofreading reduces the frequency the frequency of spontaneous mutations in bacteria
2) Mice which lack DNA proofreading have increased rates of mutations in mitochondrial DNA which leads to premature ageing in mice
Types of point mutations
1) Transition: replacement of a single BP with another BP of the SAME chemical category
2) Transversion: replacement of a single BP with another BP of a DIFFERENT chemical category
Characteristics of a bacteriophage
- genetically among the simplest organism
- have similar genetic mechanisms to the host cell
- easy to analyze, can analyze millions easily
Where does the DNA repair take place?
At a PRE-MUTAGENIC LESION
- before DNA replication takes place. At least one round of DNA replication needs to take place in order for a pre-mutagenic lesion to become a mutation
How do photodimers arise?
upon exposure to UV light, adjacent Thymine base become covalently cross linked (photodimers). Photodimers fail to base pair properly during DNA replication
What is an apurinic site?
A site in DNA without a purine base (Adenine and Guanine)
- During DNA replication there is a blank where the purine should be and base (often adenine) may be inserted OPPOSITE the blank which changes the sequence of the base pairs causing mutations
Steps in excision repair:
1) The enzyme AP endonuclease recognizes an apurinic site and cuts the strand of DNA that contains it
2) Excision endonucleases then remove cut strand (defective DNA) and adjacent DNA
3) Gap in DNA is filled by DNA synthesis
Enzymes involved in Excision repair mechanism:
1) AP endonuclease: recognizes apurinic sites and cuts the strand of DNA which contains it
2) Excision endonuclease: removes defective DNA (cut strand) and adjacent DNA
3) Gap in DNA is the filled with DNA synthesis
