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16 Cards in this Set

  • Front
  • Back
Mutation types
-Point:change in 1 bp
-Deletions/Duplications: bases are added or removed from the normal sequence
-Translocations:transfer of genes from 1 chromo location to another
Types of point mutations
-transitions:purine to purine,or pyrim to pyrim
-transversions:purine to pyrimadine (A,G->C,U,T)or vice versa
Results of point mutations
silent-trasnition,asymptomatic,codesfor same protein
nonsense-transversion,creates a stop codon,premature termination of translation, complete loss of protein function
missense-transition,changes code to a diff protein
frameshift-insertions & del of anyting other than 3bp's =shift in reading frame,premature stop codon & loss of protein function
Spontaneous point mutations
hydrolysis rxns:
-hydrolysis of glycosidic bond b/t purine and deoxyribose=no base just OH on C#1
-hydrolysis of amino grp on cytosine=uracil
tautomeric shifts:shifts durng replication
-imino form of A pairs w/C
-enol form of T pairs w/G
Deamination of methyl cytosine & deaminating agents
Both = errors in replication
-C is methylated = T
nitrous acid turns A to hypoxanthene & C to uracil
Pyrimadine dimers
-UV radiation i.e. sunlight, causes 2 T dimers to occur in the same strand of a dbl helix
Intercalating agents
-agents insert themselves b/t bases
-mutations occur as frameshifts
i.e. ethidium bromide,aflotoxin-
causes G to T =transverion=liver CA
Postreplication mismatch repair
-removes mismatches,ins & del from replication errors
-enzymes can tell old strand from new b/c old strand is methylated
2 main repair principles
-base excision=single base repair
-nucleotide excision=bulky modification
Repair mechanisms
-3'exonuclease activity=replication errors
-post replication mismatch=replication errors
-direct repair=methylated bases, pyrim dimers in bact.
-base excision=breaks bond b/t sugar & nonstandard base
-AP endonuclease= takes out empty sugar
-nucleotide excision=bulky lesions
TT dimer repair
-scan for distortion i.e. abn width of helix
-excise region
-fill in
Problems w/ repair rxns
-99% succsessful
-repair DNA pols are sloppy than in replication
-no post replication repair after a repair DNA pol
Cocayne syndrome
-defect of nucleotide excision repair for transcribed genes
-poor growth
-neuro probs
-early senility
-2 types
Xeroderma pigmentosum
-defect of genome wide nucleotide excision repair
-hyper sensitive to sun
-neuro probs
-30 yr.dec in life expectancy
-inc risk of skin CA
-7 types
XP is present if both copies of an XP gene is mutated=
1 cell provides a protein that the other cell needs & vice versa
-if no complementation then both cells are mutated in the same gene
Hereditary non-polyposis colon CA
-defect in post replication mismatch repair
-80% risk of dev colon CA
-dominant inheritance