Chapter 5 ID Terms

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Chapter 5 ID Terms
2015-02-05 15:28:14
Test One
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  1. DNA replication
    the accurate duplication of vast quantities of genetic information carried in chemical form as DNA
  2. DNA polymerase
    Nucleotide-polymerizing enzyme that uses free nucleotides as substrate for polymerization into DNA on a single-stranded DNA template
  3. Replication fork
    y-shaped structure where replication moves progressively along; here is where a multienzyme complex that contains DNA polymerase synthesizes DNA
  4. DNA helicases
    Propel themselves rapidly along a DNA single strand. When they encounter a region of double helix, they continue to move along their stand, prying the helix apart
  5. Single-strand DNA-binding (SSB) proteins
    Helix-destablilizing proteins/ bind tightly and cooperatively to exposed single-stranded DNA without covering the bases, which therefore remain available for templating; stabilize the unwound, single-stranded conformation; straighten out the strand to prevent the formatin of short hairpin helices that form in single-strand DNA
  6. Strand-directed mismatch repair
    System that detects the potential for distortion in the DNA helix from the misfit between noncomplementary base pairs. To distinguish between the parental and newly synthesized strands, the newly synthesized lagging-strand DNA contains nicks (before sealed by ligase). These nicks provide the signal that directs the mismatch proofreading system to the appropriate strand.
  7. DNA topoisomerase
    Reversible nuclease that adds itself covalently to a DNA backbone phosphate, thereby breaking a phosphodiester bond in a DNA strand
  8. topoisomerase I
    1) Topoisomerase I: produces a single-strand break (or nick_; allows the two sections of DNA on either side of the nic to rotate freely relative to each other, using the phosphodiester bond in the strand opposite the nick as a swivel point; tension will drive it int eh direction that relieves the tension
  9. topoisomerase II
    2) Topoisomerase II: forms a covalent linkage to both strands of the DNA helix at the same time, making a transient double-strand break in the helix; activated on sites where two double helices cross over each other. It breaks one double helix to create a DNA gate; the second, nearby double helix passes through the break; and, it then reseals the braek and dissociates from the DNA
  10. initiator proteins
    Begin the process of DNA replication by binding to double-stranded DNA and prying the two strands apart, breaking the hydrogen bonds between the bases
  11. replication origins
    The positions at which the DNA helix is first opened; the DNA in these contain short sequences that attract initiator proteins and stretches of DNA that are easy to open, such as A-T base pairs, which are easier to break due to fewer H bonds
  12. histone chaperones
    Multisubunit complexes that bind the highly basic histones and release them for assembly only in the appropriate context; directed to newly replicated DNA through a specific interation with the sliding clamp, called PCNA, which are left beind moving replication forks and remain on the DNA long enough for the histone chaperones to complete their task
  13. telomeres
    Special nucleotide sequences at the ends of chromosoems  that contain tandem repeats and cap the end of the chromosome to ensure no segments are lost
  14. telomerase
    sequence-specific DNA-binding proteins recognize telomere sequences and call telomerase to replenish the sequences each cell division; recognizes the tip of an existing telomere DNA repeat sequence and elongates it in the 5’-to-3’ direction, using an RNA template that is a component of the enzyme itself to synthesize new copies of the repeat; RNA-dependent DNA synthesizing protein; after extension of the parental DNA strand by telomerase, replication of the lagging strand can be completed by polymerases
  15. t-loop
    Loop formed from a protruding end that loops back and tucks into duplex DNA; provide normal ends of chromosomes with a unique structure to protect them from degradative enzymes
  16. nonhomologous end-joining
    Broken ends are simply brought togheter and rejoined by DNA ligation, generally with the loss of one or more nucleotides at the site of joining; occurs with double-strand breaks
  17. homologous recombination
    Genetic exchange takes place between a pair of homologous DNA sequences (DNA sequences similar or identical in nucleotide sequence); used to exchange bits of genetic information between two different chromosomes to create new combos of DNA sequences in each chromosome; used to accurately repair double-strand breaks; chromosome segregation
  18. hybridization or DNA renaturation
    Occurs when a rare random collision juxtaposes complementary nucleotide sequences on two matching DNA single strands, allowing the formation of a shrot stretch of double helix between them (helix nucleation)
  19. Branch migration
    Can occur after strand exchange; an unpaired region of one of the single strands displaces a paired region of the other single strand, moving the branch point without changing the total number of DNA base pairs; proceeds equally in both directions