Term
Describe Mutations
1. Purpose
2. Adaptation
3. Character |
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Definition
1. essential to provide new genetic variability
2. could not occur without mutation
-survival of the fittest
3. usually deleterious and recessive |
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Term
Types of Mutations
1. Germinal
2. Somatic
3. Spontaneous
4. Induced |
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Definition
1. sperm/egg cells
2. somatic cells (bodily cells)
3. occurring without known cause but can be predicted
(10E-7 to 10E-9 percent)
4. resulting from exposure to mutagens |
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Term
| Is mutation random or directed by stress? |
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Definition
RANDOM!
-non adaptive
-stress selects pre existing mutations
*Lederberg proved by velvet test |
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Term
| Describe Adaptive Mutagenesis |
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Definition
-actually called stationary phase mutagenesis (occurs during stationary phase)
-bacteria use error prone polymerase without repair
-still random but could provide something to aid in survival |
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Term
| Describe Reversible Mutations |
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Definition
1. Back mutations- restores sequence *rare
2. Suppressor mutations- second site mutation restores phenotype
a. within the same gene
b. within another gene |
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Term
Describe Mutations that may not influence mutation
1. Isoalleles
2. Null alleles
3. Recessive |
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Definition
1. a. silent/neutral mutation- changes base but not AA
b. conservative missense mutation- actual mutation but does not affect protein
2. no gene is produced or its non functional
-if they are recessive for the gene, it can lead to recessive lethal
3. recessive only seen in homozygous recessive
-also in hemizygous as in the X chromosome |
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Term
Describe how mutations can be harmful:
1. Reversible
2. Insertion/Deletion
3. Nonconservative Missense
4. Nonsense
5. Dominant negative
6. Gain of function |
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Definition
1. very unlikely!
2. shifts gene one base- frameshift alters reading frame
3. protein is altered by mutation
4. codes for release factor or stop codon
-protein is stopped too soon
5. gene is faulty and efficiency declines
6. gene could get new function and interfere with other genes |
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Term
Describe the following Conditional Lethal Mutations
1. Auxotrophs
2. Temperature sensitive
3. Suppressor sensitive |
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Definition
1. metabolic related lethal mutation
2. does not function at certain temperatures
-some are restrictive and others permissive
3. when the suppressor is fixed, it dies
*useful for finding out what a gene does |
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Term
| Describe the role of tautomeric shifts in mutation |
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Definition
1. G and T are normally in keto form but can shift to enols
2. A and C are normally in amino form but can shift to imino
Purines always bind to Pyrimidines
A:C
G:T
*During replication, if tautomers are present a permanent mutation can occur |
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Term
Define the following
1. Transition
2. Transversion |
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Definition
1. purine changes to purine, pyrimid changes to pyrimid
2. purine changes to pyrimidine and vice versa |
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Term
Describe the following Induced Mutation
Base Analog |
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Definition
*only during replication
-structures similar to normal bases
-increase mispairs
-encourage tautomeric shifts
-results in transitions
ex. 5-bromouracil (thymine analog)
-binds to A or G
-bidirectional transition |
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Term
Describe the following Induced Mutation
Acridines |
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Definition
*only during replication
-intercalate between stacked bases of DNA
-cause frameshift mutation
ex. ethidium bromide, acridine orange, proflavin |
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Term
Describe the following Induced Mutation
Deamination |
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Definition
-compounds like HNO2 can deaminate A, C, G
-changes structure and changes pairing
A binds to C
C binds to A
G still binds to C
*bidirectional transitions |
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Term
Describe the following Induced Mutation
Hydroxylation |
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Definition
-treatment with NH2OH causes C to be hydroxylated
-C will bind to A
-only G:C --> A:T
*undirectional |
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Term
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Definition
*determine if mutagens are carcinogens
-created by Bruce Ames to determine if chemical was mutagenic/carcinogenic
-placed mutagen to see if bacteria could grow better (revertants)
-received some false positives and negatives when comparing to mammals
-added liver enzymes to get the proper results
-concluded that the liver can change the structure making something mutagenic that wasn't or harmless that was mutagenic |
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Term
Describe following DNA repair mechanism in E. coli
Light Dependent repair |
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Definition
-absent in mammals
-UV light causes thymine dimers
-DNA photolyase uses light energy to cleave the crosslinks
(absorbs blue light) |
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Term
Describe following DNA repair mechanism in E. coli
Excision Repair: BER |
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Definition
Base excision repair (one base)
1. initiated by DNA glycosoylases that recognize abnormal bases
2. sugar/base bond cleaved leaving empty site
3. AP endonucleases and phosphodiesterases remove the remaining phosphate-sugar backbone
4. DNA polymerase and ligase repair the gap
*specific glycosylases for each base |
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Term
Describe following DNA repair mechanism in E. coli
Excision Repair: NER |
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Definition
Nucleotide Excision Repair (multiple bases)
1. initiated when 2 UvrA proteins and 1 UvrB protein recognize thymine dimer
-ATP is used to bend DNA
2. UvrA leaves; UvrC binds and makes 5' incision
3. UvrB makes 3' incision
4. UvrD removes oligomer 12 bp (DNA helicase II)
5. DNA polymerase I and ligase repair the gap |
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Term
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Definition
*back up proofreading
-knows which base is new and which is old by methylation
(newly synthesized DNA is not methylated)
1. MutS recognizes mismathc
2. MutH and MutL join complex; MutH contains endonuclease that makes incision
3. requires exonuclease
4. DNA Poly 3 and ligase repair the gap |
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