Exam 4: Mutations and DNA replication/repair Flashcards Preview

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Flashcards in Exam 4: Mutations and DNA replication/repair Deck (32):
1

Depurination

bond between purine base and deoxyribose spontaneously hydrolyzes

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Deamination

Most common is conversion of cytosine to uracil

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Pyrimidine dimers

UV light causes dimerization of adjacent thymine bases on same DNA strand

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Somatic mutation

affects only cell where mutation occurred

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Germline mutation

mutation will be passed to offspring

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Gene mutations

variations in nucleotide sequence - affect only one gene

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Chromosomal mutations

rearrangements, deletions, or duplications of chromosomal regions

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Genomic mutations

addition or loss of chromosomes

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Mutations impacting chromatin

changes in methylation of DNA or in modification of histone proteins

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Point mutations

exchange of one nucleotide for another

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Silent mutation

mutation does not result in change in amino acid sequence

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missense mutation

change in sequence results in change in amino acid sequence

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nonsense mutation

change in nucleotide sequence results in a stop codon

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RNA processing mutant

change in nucleotide sequence destroys RNA splicing site or creates a new splicing site

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Small insertions and deletions are caused by

incorrect recombination (during meiosis - unequal crossover), strand slippage during replication, and intercalating agents

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nondisjunction

incomplete separation of chromosomes in meiosis; changes number of chromosomes in cell - genome mutation

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frequency of recombination between genes on same chromosomes is an

indicator of their proximity - shorter distance between genes = lower probability of crossover occurring

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Trisomy

extra copy of a chromosome present - observed for chromosomes 13, 18, and 21 only

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Monosomy

chromosome missing - if on an autosome it is lethal

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Mosaicism

some of individual composed of normal cells, whereas other parts contain mutations - somatic mutations that occur during embryogenesis (earlier it happens = more mutant cells)

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Strand-directed mismatch repair system

newly synthesized strand contains nicks that will be filled in later
Incorrectly paired bases cause distortion in DNA double helix - repair enzymes remove incorrect base pair and nucleotides to nearest nick - DNA polymerase fills in gap

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Lynch syndrome (hereditary nonpolyposis colorectal carcinoma HNPCC)

Heritable cancer - high change of developing colorectal cancer
Caused by defects in mismatch repair system

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DNA glycosylases

recognize specific types of altered base in DNA & catalyze their removal

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AP endonuclease

recognizes that a base is missing and cuts sugar-phosphate backbone on side of missing base

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DNA phosphodiesterase

removes deoxyribose phosphate group

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Nucleotide excision repair

repairs damage caused by agents that result in large changes in the structure of DNA, i.e. pyrimidine dimers
Uses helicase/nucleases to separate and cut strand; polymerase and ligase fills in gap

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xeroderma pigmentosum (XP)

Caused by mutations that abolish or impair function of proteins required for nucleotide excision repair
extreme sensitivity of skin to sunlight, pigmentation changes, and skin cancer

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Nonhomologous end-joining

broken DNA ends (when both strands break) are brought together and ligated - causes loss of nucleotide at breakpoint

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Homologous end-joining

recombination processes used to repair broken DNA without loss of information
Use other copy of chromosome to find sequence

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Cyatarabine

Used to treat acute leukemias
converted to cytarabine triphosphate inside cells - competes with deoxyribonucleotides to bind to DNA polymerases
DNA replication and repair blocked

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Cyclophosphamide

Used to treat Hodgkin's lymphoma, lung, breast, and testicular cancers
Converted to phosphoramide mustard in liver - forms inter- and intra-strand DNA crosslinks, damage that blocks replication = cell death

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Doxorubicin

Used against a variety of tumors
forms a tripartite complex with DNA and topoisomerase II - interfers with catalytic cycle and prevents re-ligation of double stranded breaks = cell death