MCO 34-42 Flashcards
Why are bacteria good model organisms
- Haploid
- Asexual reproduction
- Short generation time
- Easy to manipulate
- Easy to store
- Grow of define media
Process of binary fission
- Cell elongates and all content increases
- Septum forms in the middle
- Growth from both sides of the cell
- They are segregated and there are 2 identical daughter cells
What is a prototroph
An organism that doesn’t require special nutritional factors
What is an auxotroph
Organisms that have mutants that impair some metabolic capabilities
What it catabolic auxotrophs
Organisms that have lost the ability to catabolise some carbon sources
What is bio-synthetic auxotrophs
Organisms that have lost the ability to synthesise amino acids, nucleotide or a vitamin
what is a conditional lethal mutants
Mutants affected in housekeeping genes, which are essential for survival
What are temperature sensitive mutants
They grow at permissive temperatures, usually 30 degrees for E.coli
what are cold sensitive mutants
Mutants that grow at high temperatures
Lamarckian evolution
If an organism uses something more it will increase. Change is directed by the environment.
Darwinian evolution
Change is spontaneous and natural selection ensures survival of the fittest. Change is randomly selected.
Luria-Delbruck experiment
- E.coli cultures were grown
- Aliquots plated on plates with T1 phage
- T1 phage kills E.coli
- Muations are already present in culture
Darwinian hypothesis
Random mutations predicts that mutants appear in culture prior to adding selective agent.
Lamarckian hypothesis
Directed change predicts that mutants appear in culture only after adding the selective agent.
Newcombe experiment
- E.coli cultures are grown
- Plated onto 2 plates and let them grow
- 1 plate is left the same and nothing is done. The other is re-spreaded.
- Both sprayed with phage
- Both are grown and colonies are counted
More colonies on the re-spreaded plate as resistant colonies are spread around.
Lederberg and Lederberg replica plating experiment
- Make many replica plates of master plate of E.coli
- Then add phage
- The position of the resistant E.coli colonies on the replica plates are always the same
Therefore the resistance mutation happens before the replica plating.
What are point mutations
A change to one base pair. This can be by substitution, insertions or deletions
Types of substitutions
Transitions and transversions
What is a transition substitution
A point mutation that changes a purine to another purine or a pyrimidine to another pyrimidine
What is a transversion substitution
A point mutation that changes a purine to a pyrimidine or vice versa.
What is a silent mutation
A change in base but no change in phenotype
what is a missense mutation
A substitution where one amino acid is substituted for another
What is a non-sense mutation
Substitution leads to a stop codon being introduced
What are inversions
When kilobases are flipped
What are tandem repeats
When part of the genome is duplicated, it can lead to the overproduction of proteins
What are transposons
Nucleotide sequences that are able to move themselves around
What are reversions
A point mutation resulting in the restoration of the original sequence
What is a tautomere
Isomers of a compound which exists together in equilibrium
What happens in an isomersation switch
The rare (enol) form of a nucleotide is reverted back to the normal (keto) form.
What is a suppressor mutation
A second mutation that results in the original phenotype being restored
What is intergenic suppression
A second mutation in a different gene to the one in which the first mutation occurs. It suppresses the phenotype of the first mutation.
What is a non-sense suppressor
Inhibits the effect of a nonsense mutation. A mutated tRNA binds with the termination codon.
They tend to translate past the normal stop codon, and produce larger proteins. They not also function correctly as they may fold incorrectly.
What is a mutagen
A chemical or physical agent causing damage to DNA
How does spontaneous mutations cause damage to DNA
Replication errors and tautomers
- Base pair slipping
- Repeat nucleotides can lead to frameshift mutations
How does deamination of bases cause damage to DNA
- Removal of am amine group which causes different base pairings
- Can be caused by nitrous acid
- xanthine pairs with C
- U pairs with A
- Hypoxanthine pairs with C
How does a reactive oxygen species cause damage to DNA
-Cause a variety of changes to DNA as they are reactive:
Oxidation and addition to double bonds
-Natural side product of aerobic respiration
-Chemical reactions caused by UV light or ionising radiation .