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2011-03-02 19:45:08

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  1. __in cells remains the best method for preparing large quantities of a particular gene or other DNA sequence.
    However, when the source of DNA is scanty or impure, the__ is quicker and more selective.
    • DNA cloning
    • polymerase chain reaction, or PCR
  2. In this technique, any specific target segment within one or many DNA molecules can be quickly amplified in a test tube.
    · With __, __can make billions of copies of a target segment of DNA in a few hrs, faster than the days it’d take to obtain the same number by screening a DNA library for a clone with the desired gene and letting it replicate within host cells.
    • automation
    • PCR
  3. __is being used increasingly to make enough of a specific DNA fragment to insert it directly into a __, entirely skipping the steps of making and screening a library.
    • PCR
    • vector
  4. In the __procedure, a __-step cycle brings about a chain reaction that produces an exponentially growing population of identical DNA molecules.
    · During each cycle, the reaction mixture is heated to __(separate) the DNA strands
    · Then cooled to allow __(hydrogen bonding) of short, single- stranded __complementary to sequences on opposite strands at each end of the target sequence;
    · finally a heat-stable __extends the primers in the 5’->3’ direction.
    • PCR
    • three
    • denature
    • annealing
    • DNA primers
    • DNA pol
  5. What would happen if a standard DNA pol were used?
    The key to automating __was the discovery of an unusual heat-stable DNA pol, first isolated from cells of a bacterial species living in hot springs that could withstand the heat at the start of each cycle.
    • the protein would be denatured along with the DNA during the first heating step ad would have to be replaced after each cycle.
    • PCR
  6. Just as impressive as the speed of PCR is its __.
    · Only minute amounts of DNA need be present in the starting material, and this DNA can be in a partially degraded state, as long as a few molecules contain the complete target sequence.
    · The key to this high specificity is the __, which hydrogen bond only to sequences at opposite ends of the target segment. (For high specificity, the primers must be at least __nucleotides long.)
    • specificity
    • primers
    • 15-20
  7. By the end of the __cycle, __of the molecules are identical to the target segment, with both strands the appropriate length.
    · With each successive cycle, the number of target segment molecules of the correct length doubles, soon greatly outnumbering all other DNA molecules in the reaction.
    • third
    • one-fourth
  8. Despite its speed and specificity, __ cannot substitute for gene cloning in cells when large amounts of a gene are desired. Occasional errors during __ impose limits on the number of good copies that can be made by this method.
    • PCR amplification
    • PCR replication
  9. When __is used to provide the specific DNA fragment for __, the resulting clones are sequenced to select clones with error-free inserts.
    Devised in 1985, __has had a major impact on biological research and biotechnology.
    • PCR
    • cloning
    • PCR
  10. __has been used to amplify DNA from a wide variety of sources: fragments of ancient DNA from frozen wooly-mammoths; DNA from fingerprints or from tiny amounts of blood, tissue or semen found at crime scenes; DNA from single embryonic cells for rapid prenatal diagnosis of genetic disorders and DNA of viral genes from cells infected with viruses that are difficult to detect, like HIV.