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45 Cards in this Set

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Original mutation aka:
“direct”
Back mutation aka:
“reversion”
Salmonella typh. that are His+ are able to make
the amino acid histadine
Bacteria that can grow on a medium lacking histadine are referred to as:
histadine positive (His+)
Why can His+ grow on a medium lacking histadine?
Because they can make their own.
Give an example of a bacteria that we use a histadine medium with:
Salmonella typh.
These bacteria can mutate from His+ to His-
Salmonella typh.
Which Salmonella typh is “mutant”, His+ or His-?
His-
Define Auxotroph
a mutant requiring a nutrient in the medium
What type of mutation is it when Salmonella typh His+ mutates to His-?
This is an ORIGINAL or DIRECT MUTATION
What type of mutation is it when Salmonella typh His- mutates to His+?
This is called a REVERSION or BACK MUTATION
How do mutation begin?
Either Spontaneously or Induced
How frequently do SPONTANEOUS MUTATIONS occur?
1/10 e10 – 1/10 e10 and Random
What brings on INDUCED MUTATIONS?
Exposure of cells to mutagens
What kinds of categorical mutagens cause mutations?
Chemical and Physical
What are the main types of mutations?
Point mutations and Frameshift mutations
Name the types of POINT MUTATIONS
Missense and Nonsense mutations
Describe Missense mutations
Base substitution, one letter gets replaced resulting in a different amino acid
What is an example of a mis-sense mutation?
Sickle-cell anemia
What is sickle cell anemia?
#6 in the plypeptide is normally Glutamic acid. The Aa is replaced by valine aa instead
Describe Nonsense Mutations
Codon that codes for AA is changed to a STOP codon
What is an example of a nonsense mutation?
Thalassemia
What is thalassemia?
The normal HG is 146 AAs. Instead there are 39 in Thalassemic cases. #40 is changed to a stop codon.
Name the types of FRAMESHIFT MUTATI0NS
Deletions and Insertions
Give an example of a frameshift – deletion mutation
cystic fibrosis (1479 instead of 1480)
Give an example of frameshift – insertion mutation
Huntington’s disease (hereditary)
Mutagens can be …
Chemical or Physical
Give two examples of chemical mutagens
nitrous acid HNO2 and 5-bromouracil 5-bU
Summarize the mutation caused by Nitrous acid HNO2
If you treat the A with HNO2, the A will no longer bond with T, but C instead. The next replication proceeds normally. Change AT pair into CG pair.
Summarize the mutation caused by 5-bromouracil 5-bU
This chemical takes the place of Thymine in the replication chain. This strand now has GCACG -> CG5-buGC -> GCGCG (the 5-bu pairs with G) change AT pair into GC pair
Give two examples of physical mutagens
Radiations: Ionizing radiation and Nonionizing radiation
What does Ionizing Radiation do?
Damage DNA and chromosomes. They also break bonds in strands. X-rays eject electrons.
What causes Nonionizing radiation?
UV
Describe Thymine dimers”
two thiamines bond, causing a “dimmer
What can a Thymine dimers do?
can cause melanoma
What are the two types of repair?
Light and dark repair
Describe light repair
visible light breaks the bond
Describe dark repair
the mutant section is cut and replaced by DNA polymerase
Describe positive (direct) selection
Take a petri dish with a medium containing penicillin and we grow bacteria – only bacteria that is resistant to penicillin will grow. This is positive selection.
What are the two types of Penicillin?
Penicillin S and Penicillin R (resistant)
What is used in the replica plating test to identify mutants?
S. typhimurium, Hist+ and hist1
What is another name for direct selection?
Positive selection
What is another name for indirect selection?
Negative selection or replica plating
Describe the procedure for positive (direct) selection
Take a petri dish with a medium containing penicillin and we grow bacteria – only bacteria that is resistant will grow. This is positive selection.
Describe the procedure for Negative (indirect) selection
Take a petri dish with a medium containing histidine – this plate is called MASTER. Both His+ and His- will grow. We prepare two plates. The first one has a medium containing Histidine. The second one with a medium lacking Histidine. We take sterile filter paper and we press it onto the colonies. We then press it clearly onto the two new plates. The medium with histadine will receive all transferred (same as master). The medium lacking Histadine will only grow the His+ colonies. The missing colonies are His-