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32 Cards in this Set
- Front
- Back
what is the mechanism for
genome mutations chromosome mutations gene mutations |
genome- nondisjunction, 10-2
chromosome- chromosome rearrangements 6x10-4 gene- single base sub 10-10 bp |
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define transition
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pur to pur or
pyr to pyr eg T-C |
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define transversion
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pur to pyr or
pyr to pur eg T-G |
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define missense
nonsense silent |
misense- changes AA in protein
nonsense- premature stop codon silent- no change in AA seq |
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what causes frameshift mutation?
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insertion or deletion of one or more base pairs
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define in-frame
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insertion or deletion in multiples of 3 bp
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define tandem repeated DNA
what are egs |
insertion of repeats
eg Fragile X > 230 CGG repeats eg Huntington's >40 CAG repeats |
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define tautomerization; how does it cause mutations?
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interconversion of isomers by proton rearrangements
cause erroneous base pairings that generate substitutions following a round of DNA replication |
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cytosine can be deaminated to form what base?
5 methylcytosine? |
cytosine-->uracil
5 methylcytosine-->thymine |
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define hotspots
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substitution to thymine can NOT be recognized by DNA repair machinery therefore 5 mCG 3 sites are hotspots- more than 30% of all single base changes have occured here
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what produces apurinic (AP) site in DNA?
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removal of a purine base and replacing with OH
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what are eg of mutations caused by depurination?
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transitions and transversion
bp deletions DNA strand breaks |
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what type of spontaneous mutation involves hotspots?
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single nucleotide runs are hotspots for insertion
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what type of mutation does HNO2 cause and via what process?
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induced mutations (environmental) via deamination
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what can alkylated G pair with? what can alkylated G cause?
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T, causing transition (c-->t)
alkylated G can cause depurination |
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define intercalating agents; what can they lead to? what is another process that can do this?
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aromatic molecules that insert between bases and stretch DNA double helix
can cause insertions addition of bulky chemical groups also leads to distortions |
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eg of DNA damage by free radical involving guanine; what is another example of hydroxyl free radical damage?
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hydroxyl radical generates 8 hydroxy guanine which causes transversion and binds with A instead of C
-can cause DNA strand breaks resulting in deletions of 1 or more bp when break is repaired by non homologous end joining |
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what can UV rays cause?
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formation of covalent dimers in form of cyclobutane ring between adjacent thymines in DNA strand, distorting double helix and impairs from DNA replication and transcription
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what protein recognizes mismatched base pairs?
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MutS- prokaryotes
hMSH2- humans |
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what is function of MutL (hMLH1 in humans)
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activates MutH which cleaves new daughter strand in vicinity of mismatch
directs excission of oligonucleotdie with MutS, Helicase and Exonuclease |
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what fills in gap and what seals strand?
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DNA pol 1 fills (beta in humans) and ligase seals strand
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what is role of DNA glycosylases in base excision repair?
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scans along DNA, cleaves N-glycosidic bond to generate free base and AP site
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what enzyme breaks DNA backbone by cleavage of phosphodiester bond after glycosylases?
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AP endonucleases
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what enzyme removes deoxyribose and creates free 3'OH and 5'P?
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deoxyribosephosphodiesterase
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what are eg of repair by base excision repair?
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deamination of adenine to form hypoxanthine and oxidation of guanine to form 8 hydroxyguanine
-removes and replaces base |
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what is function of nucleotide excision repair?
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recognize and repair damage or lesions that cause distortions in DNA double helix
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what complex is used in nucleotide excision repair? what is the function of the proteins?
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excinuclease complex
-recognize damage, helicases unwind damaged region, cleavage by 5 and 3' endonucleases on both sides of damage followed by replacement and sealing by beta polymerase and ligase |
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define transcription coupled repair and its significance
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nucleotide excision repair for actively transcribed genes thus cells maintain integrity of expressed genes preferentially
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what 2 proteins are involved in transcription couple repair?
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CSA and CSB
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describe process of transcription coupled repair
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stalling of RNA polymerase as it encounters eg thymine dimer
CSA and CSB recognize stalled RNA polymerase and it is displaced and transcription is terminated excinuclease complex is recruited by CSA and CSB to initiate nucleotide excision repair |
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define recombinatorial repair and its process- what is the significance?
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repair double strand breaks by homologous recombination- RESTORES ORIGINAL SEQ
-homologous chromosome is not damaged and recombination followed by gaps filled by beta poly and ligase form holliday junctions which are cleaved and religated to restore DNA seq |
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what proteins are involved in recombinatorial repair?
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RecA (Rad51 in humans)
RuvA, B, C |