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what are the short-term consequences of DNA damage?

1. reduced proliferation
2. altered gene expression
3. apoptosis


what are the long term consequences of DNA damage?

1. aging
2. disease


What are the two classes of spontaneous mutation?

1. errors of replication

2. spontaneous lesions- chemical changes


what kind of errors can occur during replication?

wrong base is incorporated by DNA poly

due to tautomerism sometimes thymine can be in its enol form and bind with guanine


what is bloom syndrome?

A defect in the DNA helicase enzyme

1. smaller than average
2. narrow chin, prominent nose and ears
3. facial rash
4. chromosome instability (higher risk of cancer)


What are the three main types of spontaneous dna damage?

1. depurination
2. deamination
3. oxidative damage


explain depurination?

most common

breaking of glycosidic bond between base and sugar in purine nucleotides; a purine is lost

An apurinic site is the result


explain deamination?

loss of an amine group from a base

cytosine will deaminate to uracil

but... 5-methyl cytosine deaminates to thymine; which will lead to bigger issues. (mutational hotspot)


explain oxidative damage?

a result of the production of reactive oxidative compounds due to oxidative metabolism

can lead to a transverse mutation


what can UV light lead to the creation of?

covalent linkages between adjacent pyrimdine bases on the same DNA strand.

these dimers interfere with normal base pairing and block replication


types of repair mechanisms?

1. nucleotide excision
2. base excision
3. mismatch repair


How does excision repair occur?

1. recognize damage
2. recruit endonucleases
3. region excised
4. DNA poly fills gap
5. ligase seals


xeroderma pigmentosum

autosomal recessive disorder

mutations in NER genes


base pair excision?

1. missplaced base
2. base removed by glycosylase
3. sugar phosphate removed by endonuclease
4. replace base and ligate


mismatch repair?

1) Mismatch missed by proofreading is recognized by MSH proteins
2) Repair may occur during S-phase (if missed by proof-reading) or in G2 when genome is scanned for errors
3) Excision of bases around mismatch
4) Repair by re-synthesis


how can double strand breaks be fixed?

1. non-homologous end joining

2. recombinational repair


what is the result of DNA repair gene mutation?

1. increased error rate

2. genomic stability


ataxia telangiectasia?

mutation of the ATM gene
autosomal recessive
increased cancer risk (avoid X-rays)