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45 Cards in this Set
- Front
- Back
Original mutation aka:
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“direct”
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Back mutation aka:
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“reversion”
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Salmonella typh. that are His+ are able to make
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the amino acid histadine
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Bacteria that can grow on a medium lacking histadine are referred to as:
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histadine positive (His+)
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Why can His+ grow on a medium lacking histadine?
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Because they can make their own.
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Give an example of a bacteria that we use a histadine medium with:
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Salmonella typh.
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These bacteria can mutate from His+ to His-
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Salmonella typh.
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Which Salmonella typh is “mutant”, His+ or His-?
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His-
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Define Auxotroph
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a mutant requiring a nutrient in the medium
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What type of mutation is it when Salmonella typh His+ mutates to His-?
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This is an ORIGINAL or DIRECT MUTATION
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What type of mutation is it when Salmonella typh His- mutates to His+?
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This is called a REVERSION or BACK MUTATION
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How do mutation begin?
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Either Spontaneously or Induced
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How frequently do SPONTANEOUS MUTATIONS occur?
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1/10 e10 – 1/10 e10 and Random
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What brings on INDUCED MUTATIONS?
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Exposure of cells to mutagens
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What kinds of categorical mutagens cause mutations?
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Chemical and Physical
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What are the main types of mutations?
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Point mutations and Frameshift mutations
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Name the types of POINT MUTATIONS
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Missense and Nonsense mutations
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Describe Missense mutations
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Base substitution, one letter gets replaced resulting in a different amino acid
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What is an example of a mis-sense mutation?
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Sickle-cell anemia
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What is sickle cell anemia?
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#6 in the plypeptide is normally Glutamic acid. The Aa is replaced by valine aa instead
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Describe Nonsense Mutations
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Codon that codes for AA is changed to a STOP codon
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What is an example of a nonsense mutation?
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Thalassemia
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What is thalassemia?
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The normal HG is 146 AAs. Instead there are 39 in Thalassemic cases. #40 is changed to a stop codon.
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Name the types of FRAMESHIFT MUTATI0NS
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Deletions and Insertions
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Give an example of a frameshift – deletion mutation
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cystic fibrosis (1479 instead of 1480)
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Give an example of frameshift – insertion mutation
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Huntington’s disease (hereditary)
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Mutagens can be …
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Chemical or Physical
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Give two examples of chemical mutagens
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nitrous acid HNO2 and 5-bromouracil 5-bU
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Summarize the mutation caused by Nitrous acid HNO2
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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.
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Summarize the mutation caused by 5-bromouracil 5-bU
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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
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Give two examples of physical mutagens
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Radiations: Ionizing radiation and Nonionizing radiation
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What does Ionizing Radiation do?
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Damage DNA and chromosomes. They also break bonds in strands. X-rays eject electrons.
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What causes Nonionizing radiation?
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UV
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Describe Thymine dimers”
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two thiamines bond, causing a “dimmer
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What can a Thymine dimers do?
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can cause melanoma
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What are the two types of repair?
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Light and dark repair
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Describe light repair
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visible light breaks the bond
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Describe dark repair
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the mutant section is cut and replaced by DNA polymerase
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Describe positive (direct) selection
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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.
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What are the two types of Penicillin?
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Penicillin S and Penicillin R (resistant)
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What is used in the replica plating test to identify mutants?
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S. typhimurium, Hist+ and hist1
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What is another name for direct selection?
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Positive selection
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What is another name for indirect selection?
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Negative selection or replica plating
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Describe the procedure for positive (direct) selection
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Take a petri dish with a medium containing penicillin and we grow bacteria – only bacteria that is resistant will grow. This is positive selection.
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Describe the procedure for Negative (indirect) selection
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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-
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