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DNA repair is divided into two types:
1. _____-_____ repair pathways, which prevent mutations
2. ____-_____ repair pathways, which risk introducing mutations
- 1. Error-proof
- 2. Error-prone
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_____-_____ DNA repair pathways include: methyl mismatch repair, photoreactivation, nucleotide excision repair, base excision repair, and recobinational repair
Error-proof
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____-____ DNA repair pathways operate only when damage is so severe that the cell has no other choice but to die.
Error-prone
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______ _______ repair is based on recognition of the mehtylation pattern in DNA bases.
Methyl mismatch repair
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Methyl mismatch repair uses methylation of the ______ strand to discriminate from newly replicated DNA under the premise that this strand will contain the proper DNA sequence.
parental
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The methyl-directed mismatch repair proteins (and genes) are called ____ because a high mutation rate results in strains that are defective in one of these proteins.
Mut
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A bacterial strain with a high mutation rate is called _____ strain.
mutator
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_______ is a type of error-proof repair pathway which involves the enzyme photolyase biding to the pyrimidine dimer and cleaving the cyclobutane ring.
Photoreactivation
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_____ _____ repair is a type of error-proof repair pathway which involves an endonuclease removing a patch of single-stranded DNA containing certain types of damaged bases, including dimers. (Uvr proteins)
Nucleotide excision
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Name the type of error-proof repair pathway:
- specialized enzymes can recognize specific damages bases and remove them without breaking the phosphodiester bonds
Base excision repair
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Base excision repair results in an abasic site, or AP site (______ or ______), which can be recognized and cleaved by a specific AP endonuclease.
apurinic, apyrimidinic
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During base excision repair, the AP site allows ___ ____ __ to synthesize a replacement strand containing the proper base.
DNA Pol I
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Name the error-proof repair pathway;
- takes place at the replication fork
- a single-stranded segment of the undamaged daughter strand can be used to replace a gap in the damaged daughter strand, which is carried out by RecA
- Not limited to pyrimidine dimers
- It will work on any damage that causes gaps during replication
Recombinational repair
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Name the error-prone DNA repair:
- induced by extensive DNA damage
- RecA coprotease activity stimulates autodigestion of the LexA repressor
- Expression of many DNA repair enzymes
- Among them, two "sloppy" DNA polymerases that lack proofreading activity, however the cell has no other option but "mutate or die"
SOS ("Save Our Ship") repair
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Name the error-prone DNA repair:
- common in eukaryotes
- found in some bacteria such as Mycobacterium and Bacillus
- May cause loss or addition of a few nucleotides or even the joining of two previously unlinked DNA molecules
Nonhomologous end joining (NHEJ)
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