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10 Cards in this Set

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Spontaneous damage to DNA
-arise during cell growth
1)deamination-loss of amine(NH3), converts A,G,C to U,HX,X. Refered to as TRANSITION MUTATION-pyr to pyr or pur to pur
*TRANSVERSION MUTATION-pyr to pur or pur to pyr
2)Base loss-10,000/cell generation, bases fall off, but phosphodiester backbone remains, pur more sensitive thatn pyr, can lead to strand breaks
3)Reactive Oxygen Species(H2O2)-are or cause O w/ unpaired e- (free radicals), caused by:respiration or ionizing radiation. Damage by: cleaving deoxyribose sugar or p backbone-strand break, OR damaging base-replication block or mispairing. Removed by: enzymes or reducing agents
Exogenous sources of DNA damage
a)ionizing radiation-gamma or x-rays, forms ROS, causes clustered strand breaks
b)UV light-photoactivates nucleotides, causes covalent bonds b/w adj bases-> kiinks DNA can block transc., replic, lead to mutation
2)Carcinogens: adduct formation-covalent attachments to NT-bulky, interfere w/ replic, or transc
a)alkylating agents-reactive C containing chem, add methyl,ethyl, or bigger group to base-disrupt DNA struct. can alter base pairing
b)Cross-linking agents-bifunctional agents-have two adduct forming groups, bond to two positions on DNA in 1 strand or 2 diff. interstrand completely block transc. and replic.
Errors in DNA replication
1)polymerase error-misincorporation of NT by pol b/c of tautomers(enol T pairs w/ Keto G, amino A pairs w/ amino C), <1x10^6
2)repeat/microsatellite instability-primer slips in highly repetitve DNA, causes buldge-->expans or deletion of seq
problem in mismatch repair/disease
-fixes replication errors-substitutions, slippage
-not obvious which strand is damaged
-don't know when error was made and could be on template
-HNPCC(hereditary nonpolyposis colorectal cancer)-mutation in mismatch repair factors
double stranded break repair
1)homologous recombination
-chromes found in homologous pair=one maternal,one paternal-each made up of chromatid pair
2)End-Joining/Illegitimate Recombination
homolugous recombination basics
1)make a double strand break
2)at region of break, align the equivalent unbroken region from either intact homologous chrom(meiosis) or intact sister chromatid(mitosis)
3)Use the intact homologue or sister chromatid as template for repair
meiotic homologous recombination
-always homologue repair to mix and match mat and pat chromes
-recombination causes: Gene conversion(sub one in, and loose one-AB/ab->Ab/ab) or Gene Cross-over (AB/ab->ab/AB)
mitotic homologous recombination
-ds breaks are accidental
-use sister chromatid for repair template
-conservative recombination(unless-unequal sister chromatid exchange in repetitve seq)
-more accurate
-requires S phase
End joining repair
-easy way
-nuclease get rid of damaged ends
-polymerases make ends compatable
-ligase works w/ polym to reconnect
-doesn't require a lot of E or sister chromatid
-less accurate-no template can cause translocations
-package RNA into virus-can infect new cell(extracillular phase of life cycle)
-transcribed by RNA polymerase into ssRNA copy of genome, this copy is conv. into DNA by reverse transcriptase
-prefer insertion near or in active genes
-Once integrated disrupt host gene: Directly-integrating within gene and messing up translation OR Indirectly-integrating near gene, transc. enhancers in retroviral genome-overexpression
Retrovirus may lose its genes, pick up other genes: cause transduction of host genes or parts of host genes
**-retroposons have no viral phase, remain intracellular