Lecture 5 - DNA R,R,R pt 1 Flashcards
How does cell control mutations in somatic and germline cells during replication? **
Proofreading, 3’ to 5’ exonuclease.
How does the cell fix damage that occurs before replication occurs or cell division?
NER, BER, NonHR, HR
What are types of spontaneous DNA damage
- Depurination hydrolysis of N-glycosly inkage b/w guanine and deoxyribose = base removal
- Deamination - amine froup on cytosine is hydrolzed into ammonia na dleaves carbonyl PRODUING URACIL
- Uv radiation causeing formation of pyrmidine dimers (TT and CT)
- all of these lad too deletion or base oarisubitistion
What are the differences b.w the types of repair
BER - single nuleotide repair
NER - portion of DNA are repaired
TCR (transcription coupled repair ) - recruits DNA repair to transcribed RNA (ATM)
WHat is base excision repair?
- DNA GLYCOLSYLASES scan for URACIL
- enzyme mediated flipping of base
- the glycosyl bond is cleaved no base-sugar bond
- via AP endonuclease and phosphodiesterase cuts and removed backbone)
- DNa poly
- ligase
what is Nucleotide excisiton repair?
- pyrimdine dimer identified w/ multienzyme comlplex
- excision nuclease makes cut on both sides
- helicase takes away mutated portion
- DNA poly and ligase clean up
What is transcription coupled repair and whats one diease that results in it?
- cell mediated
- RNA poly stalls at lesions and directs repair machinery
- works with BER,NER,HR,nonHR
- Results into COCKANYES SYNDROME
- defective TCR,
- RNA poly is permanetly stalled at sites of damage
- growth retardation,skeletal abnormalities, sensetitivty to sunlight
What is one primary reason why RNA is not used as hereditary information?
If we used RNa as Primary hereditary infor. Deaminiation of cytosine to uracil would be undetecable from right or wrong
WHat about DNA modification is problematic?
Methylated cytosine causes it to become thymine
there are 3% of methylated cytosines but they cause 1/3 of all point mutation assocated with inherited diseases
What are translesional Polymerases and when are they used?
Used when the cell has sustained extensive damage.
Ex the Jr varsity team to DNA poly high school
Less accutate but they make corrections when a portion of DNA is destroyed eventually DNA poly does come and take over
Lack of endonuclease proofreading activiy
know this ish
What is DS break repair/
Double strand break in DNA. Repaired via two processes
Non homolougous Cell joining and homologous recombination
What are some causes of DS breaks?
ionizing readiation
replication errors (fork falls apart)
Oxidizing agents
other metabolites that cut DNA
What do humans use as the prefered fix for a DS break?
nonhomologous end joining
WHat is non homolougous end joining?
Cell finds DS break
Ends of break are process and joined together
EFfects:
you dont know what you lose but little of the genome are exonic
What are the checks points in the cell cycle?
DNa damage triggers are identified by checkpoints
Checkpoints insure the completeion of the one stage of the cell
- blocks entry g1 into S
- slowing down of S phase
- block transition from g2 into M
What is ATM?
a kinase that generates intracellular signals that alert the cell to DNA damage and upregulate expression of DNA repair genes
mutationns lead to ataxia telengiectasia
Why do we use homologous recombination
- fix DNA breaks
- Stalled or broken replication forks
- occurs b.w homologous DNA in meiosis
- genetic variation
- mechanical role fundamental to all organisms
how are heteroduplexes formed?
DNA DS strands look for “similiar DS strand (homology)” via sampling EA. other
DNa double helices hybridize (renature) w/ each other
HOmology is found when 15 nucleotides BP up
Heteroduplex created
How many nucleotides to form a heteroduplex or show homoogy?
15
What are the steps of homologous recombination?
ds break is process to produced 3’ overhangs via exonuclease
3’ of broken strand invades the other (heteroduplex) VIA RAD51/RECA
DNA polymerase synthesizes finishing off length of invader
invader returns back home
ligase
What conducts strand invasion?
- BACTERIA its Rec A + other proteins
- tightly controlled & REQUIRES ATP
- Ieukaryotes its RAD 51
- REQUIRES ATP
What happpens when you lose control over regulation of HR
- Loss of heterozygosity
- use of non functioning homologs to repair
- Leads to cancer
How is HR regulated?
- Exonucleases required for creating the 3’ overhang are only active in S and G2
- allows for cell to know replicated chromosome will be the one targeted for repair
- Loading of recA and Rad51 is controlled
- Repair proteins dispersed through cell
What are two examples of mutations in recombination?
- BRca1 - regulates the processing of broken ends of chromosomes
- mutation in BRCA1 lead to use of non homologous end joining
- BRCA2 maintains Rad 51 (recA) incactive unit it is at the site of damage
- Mutation causes it not to bind to DNA to form invading strand.
KNOW THIS!!!
