DNA Mutations + Repairs (Chap 7 ) Flashcards
altered phenotype
- gene mutated transcripted + translated
Mutation def
- change in DNA base pair or chromo
- > somatic : affect only ind
- > germline: alters GAMETES and next generation
Mutation rate
# of mut per cell division - ie # of mut per gene per generation
Mutation frequency
- # of mut per total cells in defined pop
Point Mutation types
(single base pair mutation )
-substitution:
-> Transition: change b/n pur-pyr and another pur-pyr
-> Transversion: change b/n pur-pyr and to pyr-pyr
-Insertion+delections:change in reading fraom mRNA downstram mutation=framshift
(truncation, elongation, jibberish)
-> missense : change norm codon to dif one=dif a.a.
-> nonsense : change codon to STOP = premature termination= truncated protein
-> neutral/silent : sim a.a is inserted= no change of protein function
Reverse + Suppressor Mutation
- pt. Mut.
- > forward “ : change genotype from wt to mutant
- > backward”:change genotype from mutant to wt/true or partial wt
Supressor mutation
- @ sites dif from orignal mut
- > mask or compensate for initial mut
a) intragentic suppressor: @ same gene but dif site then orgi
b) from dif gene=== supressor gene
Spontaneous Mutation
(not induced by mutagen)
- during G1,S,G2 or movement of transposen
- repaired effectively and don’t stay in genome
Deproination +Deamination
- loosing purine from DNA: breaking bond + deoxibose in backbone, common b/n sugar and purine, if not repaired before replication DNA polymerase will stall
+
-remouves amino group
= DNA lesions
Induced Mutation
exposed to :
1.) physical
->radiation:
–> nonionizing : UVlight (dimer formations= buldge in DNA and disrupts replication)
–> ionizing: X-ray,cosmic ray, Radon(causes chromosom mut and death)
–> Dose and mutaion rate: linear and cummal effect ie radon gas
or
2.) chem mutations:
–> base analog: sim to normal base and readily absorbed ie transition mut of 5-Bromouracil
–> base modifying agent: hydroxylating (modifies OH- of C), Alkylating (add alkyl group to G), interclating (insert b/n bases of DNA= causes framshifts)
Repair to DNA damage
- direct reversal: mismatch repair, photoreactivity, repair of allkylation
- excision repair “”: base excission, nucleotide, methyl-directed mismatch repair, translession dna synthesis and sos response
environmental mutagens
- chem mutagens (frequent activity in liver)
- -> cause reversion mutations and increase grows w/out histones
screening for toxins
Ames test: determine chem carcinogencity
–> auxtrophy - inability for org to make particular organic component required for growth
mismatch repair
- DNA pol proofre and corrects
- e.coli : ‘ 3-5, exonucleus affirmed by mutator
- -> mutD gen encodes epsilon subunit of poly III
photoreactivity ( light repair)
- repair UV induced pyrimidine dimer
- uv activates phltolylaseto solit dimers
- humans dont have photolylase
alkylation damage ( methyl or ethyl groups)
- DNA enzyme can remove damage
- methyltransferase
base excision repair
- glycolase recognize and remove damage
- base removed from sugar backbone
- -> produces gap where pol and ligase inserts base
nucleotide excision repair
- UvrA +B scan and fix damage
- UvrB +C cut it out
- UvrD unwind helix and release damaged
- ligase and DNA pol finish
- UvrA +B scan and fix damage
methyl-directed mismatch repair
- recognise +excise+repair
- > IDs nascent DNA(unmethyllated)
ie . E.Coli 1.mutS binds= complex w/ mutH and mutL
- dna= contorts
- mutH nicks dna+ excises exonucleous
- dna pol+ ligase finish
translesion DNA synthesis
(last reslrt mec)
- allow cell to survive when speckfic baseair cannot lccur
- SOS = lexA+ recA genes turn on ( facilitates dna pol translesion synth)
- -> dna damage = recA activated=> lexA tl self digest +lexA stops mediating dna repair
