ch 16 genetics terms

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ch 16 genetics terms
2011-12-13 09:14:55
terms definitions 16 genetics

BIOL 350 term identification
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  1. point mutation
    refers to the alteration of a single base pair of DNA or of a small number of adjacent base pairs
  2. transition
    replacement of a base by the other base of the same chemical category; ex A to G or G to A and C to T or T to C
  3. transversion
    replacement of a base of one chemical category by a base of the other; ex purine (A or G) replaced by pyrimidine (C or T)
  4. syonymous mutation
    the mutation changes one codon for an amino acid into another codon for that same amino acid. AKA silent mutations
  5. missense mutation (conservative)
    The codon for one amino acid is changed into a codon for another amino acid, but the altered amino acide is chemcially similar
  6. missense mutation (nonconservative)
    The codon for one amino acid is changed into a codon for another amino acid, and the amino acid is chemically dissimilar
  7. Nonsense mutation
    Altered codon signals chain termination, i.e. STOP codon
  8. Frameshift mutation
    insertion or deletion of a single base pair of DNA which changes the reading frame for the translation process, causing the entire amino acid sequence downstream of the mutant site to bear no relation to the original amino acid sequence. Typically result in complete loss of normal protein structure and function
  9. tautomers
    isomers that differ in the positions of their atoms and in the bonds between the atoms; each of the bases in DNA can appear in one of several forms, called tautomers
  10. keto
    form of each base that is normally present in DNA
  11. spontaneous lesions
    naturally occurring damage to the DNA that can generate mutations
  12. depurination
    the more commone form of spontaneous lesion. The loss of a purine base.
  13. deamination
    deamination of cytosine yields uracil when H2O is transitioned into NH3
  14. oxidative damage
    a mechanism of spontaneous lesion that is a side effect of aerobic metabolism. The active oxygen species can cause damage to DNA as well as to DNA precursors, resulting in mutation.
  15. mutagenesis
    production of mutations in the lab through exposure to mutagens
  16. base analogs
    some chemical compounds are sufficiently similar to the normal nitrogen base of DNA that they occasionally are incorporated into DNA in place of normal bases. They are incorporated into DNA during DNA synthesis. They have pairing properties unlike the normal bases, thus they can produce mutations by causing incorrect nucleotides to be inserted during replication.
  17. three mechanisms of mutagenesis
    replace a base; alter a base to mispair; damage a base so no pairing can occur
  18. forms of base damage
    • UV light: generates alteration in DNA called photoproducts
    • Ionizing radiation: formation of ionized and excited molecules that can damage DNA, or more commonly, cause breakage of bonds
    • chemical carcinogens: bulky addition products cause breakage between base and the sugar
  19. intercalating agents
    planar molecules that mimic base pairs and are able to slip themselves in between the stacked nitrogen bases at the core of the DNA double helix. In this position, it can cause insertion or deletion of a nucleotide pair
  20. direct reversal of damaged DNA as a biological repair mechanism
    The most straightforward way to repair a lesion is to reverse it directlly, regenerating the normal base. Most damages are irreversible, but some can be fixed. Alkyltransferases remove alkyl group, and photolyases split pyrimidine dimers
  21. homology dependent rapair systems
    repair using sequence complementarity to replace damaged bases.
  22. base-excision repair
    damaged bases are removed and repaird through sequential action of DNA glycosylase(cleave base-sguar bonds), AP endonuclease (cuts damaged strand upstream), dRpase (cleans up backbone), DNA polymerase (refills backbone gap with nucleotides), and ligase (seals new nucleotide into backbone)
  23. nucleotide-excision repair (NER)
    repairs bulky damage; activated when global genomic repair (GGR) recognizes nontranscribed regions, or when Transcritpion-coupled NER (TC-NER) finds transcribed regions of the genome. A multiprotein complex then excises several bases and resynthesizes them using the opposite strand as a template
  24. mismatch repair
    • - conserved from bacteria to humans
    • - corrects replication errors in newly synthesized DNA
    • -100fold decrease in replication errors
    • Mismatch repair system have to do at least three things:
    • 1) recognize mismatched BP 2) determine which base is incorrect 3) excise the incorrect base and carry out repair synthesis
  25. translesion polymerases
    accommodate damaged bases; in general have a higher error rate; dissociate after adding a few nucleotides
  26. nonhomologous end joining (NHEJ)
    One method used to put double standed broken ends back together. Error-prone. 1) recognize damage 2) KU70 and KU80 bind to broken ends, forming heterodimer 3) ligase joins the two ends.
  27. synthesis-dependent strand annealing (SDSA)
    error-free repair mechanism that can correct damage if the break in the double strand occurs after replication of a chromosomal region in a dividing cell. It uses sister chromatids available in mitosis as the templates to ensure a correct repair

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