genetics test 2 ch 16(18) repeat expansions
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_ _ _ expansion of 3-base repeat
- Fragile X disease
- - dominant, X linked
- CGG, changes in # of repeats in the untranslated region of
- FmR-1 gene (retardation) - product regulates translation of other protein, plays a role in development of synapses.
- BER: Base Excision Repair
- repair oxidative damage, UV photo products uracils DNA
step 1 enzyme N-glycosylase recognizes abnormal base, cleaves btwn base and sugar.
step 2 Endonuclease recognizes gap (missing base), nicks backbone on 5' side
step 3 5' to 3' exnuclease removes base
- nucleotide excision repair
- Fix many types mutation, thymine dimers, missing bases, chemically modified bases.
- * uses different enzymes than BER
- * Removes more bases than BER
- 1. UVrA,B scan DNA, recognization of bultky lesions
- - 20-50 copies in cells
2. UVrB binds to damage site, cause uVrA to dissociate
Recruits UVrC, binds to UVrB, makes dual cut in DNA.
Xerodema Pigmentosum (XP)
- -autosomal recessive
- -caused by mutations in NER proteins
- -typically 8 or more genes
- - features of disease result of a build up of unrepaired DNA (UV damage)
- mismatch Repair
- * fixes mutations that polymerase should have found. (3' to 5' proofreading)
- 1. Recognize mismatched base
- *2. Determine which is the incorrect one
3. Excise incorrect base, carry out repair synthesis.
- Replication errors produce miss-match on newly synthesized DNA.
- methylate DNA @ Adenines in GATC sequences
- * Directly after replication, the DNA is hemi-methylated, lag time before adenine methylase adds CH3
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