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48 Cards in this Set
- Front
- Back
Base Excision repair is what?
enzymes involved? |
repairs damage to a single nucleotide. base is removed with glycosylase and replaced with DNA ligase
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nucleotide excision repair is what?
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repairs damage 2–30 bases. thymine dimers SS-breaks. UvrABC endonuclease
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NER Transcription-Coupled Repair (TCR)
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Deploys high-priority NER repair enzymes to genes that are being actively transcribed.
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DNA polymerase I
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103kD mass. 600 turnover number, Pol A structural gene. Conditionally lethal. polyermizes. Exonuclease 3 to 5 and 5 to 3.
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non-homogenous end-joining
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a proenzyme binds to random DNAs joints them together after making them fit by cleaving frayed ends
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SOS response
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when a cell stopds dividing to specifically repair damaged DNA
error prone and mutagens able to have no proofreading by active Pols |
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Methods to repair DS-DNA breaks
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recombination repair and non-homologous end-joining
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Transposons
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mobile genetic elements
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homologous recombination
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two aligned strands are nicked and makes cross over to pair with near complementary strands to make heterlogous DNA by which DNA ligase repairs. Known as holiday junctions.
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recombination repair
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1)A single nick breaks during replication fork.
2) RecBCA+ ReA mediated inversion 3)Branch by RuvAB makes holiday junc 4) RuvC resolved holiday junction leaves repication fork in tact. primers |
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homologous end-joining
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double holliday junction fices DNA break
-DNA synthase and ligase -resolved to yield 2 intactstrands |
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3 transposon types
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-insertion sequences
-transposons and regulation -genes not involved in transposon moved -composite transposons |
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mechanism of transposons
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1) staggered ss-cuts made in both strands
2) Each fray end binds to the DNA to form replication fork. 3) replication occurs to make a cointigrie (plasmid fusion) 4)cointigrie resolved into 2 plasmids by resolvase. |
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DNA demethylation
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transfers matheyl group to Cys residue and is inactivated
O6-alkylguanine-DNA alkyltransferase |
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Base Excision Repair. most frequent type
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if DNA glyocolase cleaves glycoside bond leaving a ribose with no base. deoxyribose cleaved by AP endonuclease and gap filled in with DNA polymerase or Ligase
-Uracil DNA glycosylase is most frequent occuring. |
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UV causes
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formation of hydroxyl radical or pyrimidine dimers
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examples of chemical mutagens and what they do
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HNO2 nitrous acid deaminates.
Adenine->hypoxomethene -=C Cytosine->Urical:A DNA strands break by ROS |
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Thymine Dimer
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UV light causes a cyclobutyl ring between 2 stacked thymines
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2 classes of chemical mutation
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Point mutations: 1 BP replaced by a different one.
Transitions: Purine replaced by purine or pyrimidine Transversions: purine replaced by pyrimidine or vice versa. Insertion/Deletion: a pair is removed or added. |
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Projeria
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disease of rapid premature aging resulting in childhood death. Short telomeres.
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Mutation
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an inheritable alteration of genetic information
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how are tolomeres replicated
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telemorase makes a segment in a way similar to that of reverse transcriptase
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telemorase and cancer
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good drug target for cancer and leads to death of over proliferating cell
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Initiation of Euk. DNA replication
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One initiation->5-300kB
replicions->cluster of irigin sites (20-80/chrom) cluster activated ->Helicase binds, SSBholds as SS and DNA Pol-a binds puts RNA primer eplaced by pol-sigma |
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Elongation of Euk. DNA replication
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Pol-sigma goes bidirectionally until another fork is met
Histone_dissociate when fork approaches and join when fork passes with correct pair made for DNA RNase H1 removes RNA leaving 1 5'-RNA cleaved by flap endonuclease-1 (FEN1) |
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four ways cells maintain genetic info accurately(bacterial)
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1) Balanced dNTP's levels
2) 2 step pol III activity 3) pol I and III 3'-5' exonuclease activity to repair 4) DNA repair systems |
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Euk Replication.
DNA pol a DNA pol-sigma DNA pol- gamma |
alpha-associates w/ primase lays RNA primer to 15 DNA. No exonuclease activity
Sigma-(pol III) associates with sliding clamp(PCNA) and elongates DNA Gamma-Only in mutochondria |
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Pol III holoenzyme
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polIII+B subunit(sliding clamp) the B clamp keeps pol III on DNA
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Then replicaiton is terminated
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When a segment of DNA codes for replication to step and release complexes two replication forks sites (TerC) by TUS protein which promotes helicase activity
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Then DNA (2 DS DNA) separated
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Topoisomerases unlink DNA
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Replisome
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Large complex containing 2PolIII enzymes.
T2 lies between |
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Elongation-synthesis of leading and lagging strands
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Replisome moves along 5'-3'
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Pol I note
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Replace DNA fragments
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How is bacterial relication started?
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specific resides one bound by DNa A binds DNA B(a helicase) to unwind DNA then SS binding protein (SSB) holds it in SSDNA conformation
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DNA Gyrase(type II topoisomerase)
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undices negative supercoiling to facilitate dsDNA->ssDNA
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Role of primosome. What is it?
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DNA-B-DNA-G complex
primase->sunthesizes RNA primer for first part of leading strands and each okazaki fragment ~11 nucleotides long |
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DNA Pol I
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adds nuclotides in 5'-3' direction editing mistakes in both 3'-5' and 5-3
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DNA pol II
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DNA repair
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DNA pol III
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Replicates DNA in 5'-3' direciton cant nrepair dsDNA
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Nucleotide Excision Repair
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responds to helix distortions when UvrABCendonuclease cleaves damaged DNA UVrD displaces fragment and DNA added by Pol I and DNA ligase
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Xeroderma Pigmentosa
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disease which NER(nucleotide exicison repair) wasnt functioning leading to sensitivity to sunlight and eye damage.
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semiconservative replication
-Who discovered |
1/2 of old DNA strands joints newly synthesized strands.
Meselson and Stahl |
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DNA extends how? which direction?
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5'-3'. both directions
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2 nnames to designate strands
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leading and lagging strand
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Ames Test
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a strain of bacteria that is his-(cant make histidine) a suspected mutagen is spread with cells and # of abnormal cells is how carinogenic it is and liver is added to simulate normal metabolism
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How pyrimidine dimeres restored to monomers?
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DNA photophosphorylase
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Cockayne syndrome
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hypersensitivity of UV radiation, stunted growth developmental disabilities because of a distored DNA template.
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Mismatch repair
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Mut, Mut G combine on mismatch to make a leap where mut H and UvRd and endonuclease break off 2 strand where pol III replaces with good DNA
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