Restriction enzymes and characterizing DNA.


  1. A genetic map is

    a listing of all possible genes of an organism.

    a relative positioning of genes relative to each other as defined by the genetic nearness of mutations to one another.

    an absolute correlation of genes with their locations on chromosomal DNA.

    a listing of only the genes that have been identified by mutations.


  2. A restriction map is

    a positioning of genes on the chromosomal DNA molecule relative to restriction sites in the DNA.

    a map that shows the locations of genes that are not subject to mutation and whose analysis is subsequently restricted.

    the positioning relative to each other of restriction sites in a DNA molecule.

    a listing of all known restriction enzymes and the sequences those enzymes recognize and cleave.


  3. A restriction map must always be based on

    the location of the beginning of the gene of interest.

    the orientation of the DNA fragment that codes for the gene of interest.

    the exact distance between restriction sites.

    restriction enzymes that cleave within the DNA fragment of interest.


  4. Preparing a restriction map of a DNA fragment that includes two different restriction enzymes ResA and ResB involves

    digesting the DNA separately with ResA and ResB and comparing the sizes of the resulting DNA fragments.

    digesting the DNA simultaeneously with ResA and ResB and comparing the sizes of the resulting DNA fragments.

    digesting the DNA both separately with ResA and ResB and simultaeneously with ResA and ResB and comparing the sizes of the resulting DNA fragments.

    determining the nucleotide sequence of the DNA fragment, then using a computer program to locate the cleavage sites for ResA and ResB.


  5. DNA fragments generated by restriction enzymes are often examined by gel electrophoresis, a process based on the principle that

    small DNA fragments move faster than large DNA fragments in an electric field.

    small DNA fragments move slower than large DNA fragments in an electric field.

    in an electric field, small DNA fragments move faster through a gel matrix than do large DNA fragments.

    in an electric field, small DNA fragments move slower through a gel matrix than do large DNA fragments.


  6. The major functional difference between agarose and polyacrylamide gels is

    the higher pH at which the polyacrylamide gels must be run.

    the higher temperatures at which the agarose gels can be run.

    the greater size dimensions of agarose gels.

    the smaller matrix pores of the polyacrylamide gel.


  7. DNA fragments in an agarose or a polyacrylamide gel can be visualized by

    direct examination of the gel under the correct wavelength of visible light.

    direct examination of the gel under the correct wavelength of ultraviolet light.

    staining the DNA in the gel with certain dye compounds, followed by direct examination under the correct wavelength of visible light.

    staining the DNA in the gel with intercalating compounds, followed by examination under the correct wavelength of ultraviolet light.


  8. The relationship between DNA fragment size and mobility in an agarose gel is best described as a

    linear relationship between size and mobility.

    an approximately logarithimic relationship between size and mobility.

    strongly dependent on the concentration of agarose in the gel.

    independent of the voltage and current conditions used during electrophoresis.


  9. The purpose of the presence of a DNA fragment size standard, such as bacteriophage lambda DNA digested with HindIII, is

    to provide a set of DNA fragments of known sizes whose mobility can be measured and graphed to provide a standard curve.

    practice encouraged by suppliers of DNA standards to ensure continued product sales.

    to verify that each gel has performed as expected without error in gel preparation or electrophoresis conditions.

    practice that should only be followed when the sizes of unknown DNA fragments on the gel must be determined.


  10. The relative mobility of DNA in an agarose gel is most strongly dependent on the

    percent GC composition of the DNA molecule.

    the size of the DNA molecule.

    both the size and conformation of the DNA molecule.

    the pH of the electrophoresis buffer in the gel.


  11. Gel electrophoresis reveals that a 4000 bp DNA fragment digested with EcoRI gives fragments of 1000 bp and 3000 bp and the same apparent fragments when digested with HindIII. The best description of the restriction map of this fragment would be that

    the EcoRI and HindIII sites occur very near each other 1000 bp from the left end of the fragment.

    the EcoRI and HindIII sites occur very near each other 1000 bp from the right end of the fragment.

    nothing can be determined about the restriction map of this DNA fragment.

    the restriction map of this fragment contains an EcoRI site 1000 bp from one end of the DNA fragment and a HindIII site 1000 bp from one end of the fragment.

    the restriction map of this fragment contains an EcoRI site 1000 bp from one end of the DNA fragment and a HindIII site 1000 bp from the other end of the fragment.


  12. Agarose gel electrophoresis reveals that a 2000 bp covalently closed circular DNA molecule is converted to a 2000 bp linear DNA band when digested with EcoRI but appears as a 1000 bp band when digested with HindIII. This might be adequately explained by

    the presence of 2 HindIII located on opposite sides of the circular molecule, giving rise to two 1000 bp fragments that migrate as a single band.

    the presence of many HindIII site, two of which generate a 1000 bp fragment, while the others generate many small fragments that are not revealed by the agarose gel.

    the use of an enzyme other the HindIII.


  13. As the same of the genome of an organism increases, the number of DNA fragments generated by digestion with restriction enzymes and detected by gel electrophoresis will generally

    increase.

    decrease.

    stay about the same regardless of the size of the genome.

    will always allow resolution of all of the individual fragments that together comprise the genome.


  14. The preparation of detailed restriction maps can entail the digestion of a DNA sample under salt or pH conditions that are not optimal for a particular restriction enzyme, a practice that is relevant to the "star" activities of certain restriction endonucleases. These "star" activities can be described as

    irrelevant because they do not interfere with accurate generation of restriction maps.

    present in enzymes that work in a wide range of digestion conditions and are resistant to digestion artefacts.

    the recognition and cleavage of nucleotide sequences larger and more specific than the normal recognition site.

    the recognition and cleavage of nucleotide sequences smaller and less specific than the normal recognition site.


  15. The statistical frequency of the occurence of a particular restriction enzyme cleavage site that is 6 bases long can be estimated to be approximately

    once every 4096 bases.

    once every 1024 bases.

    once every 256 bases.

    once every 24 bases.


  16. The restriction enzymes that are most useful for mapping very large DNA fragments are

    enzymes with cleavage activity that is inhibited by DNA methylation.

    enzymes with large (greater than six bp) recognition sites.

    enzymes with small (less than six bp) recognition sites.

    those enzymes that are commercially available.


  17. The enzymes EcoRI (GAATTC) and HindIII (AAGCTT) both recognize a sequence containing two A's, two T's, one G, and one C, yet it is possible to isolate natural pieces of DNA that are thousands of base pairs long and are cleaved many times by one enzyme but not at all by the other. This might be explained by

    the isolation of the DNA from a host that contains a methylase that modifies the DNA and prevents cleavage by one of the enzymes.

    the fact that biological restraints may exclude the use of certain nucleotide sequences in some DNA molecules.

    the observation that some nucleotide sequences may occur preferentially in certain DNA sequences.


  18. Features that are important to the use of Type II restriction enzymes for mapping of DNA sequences include

    specificity of recognition and cleavage.

    the short cohesive DNA termini generated by digestion.

    relative ease of purification and stability of the proteins.

    the ability to reseal the termini to make new DNA molecules.


  19. The wide variety of sequence recognition and cleavage specificity that is currently commercially available is a

    result of the genetic engineering of enzyme specificity by the companies that sell restriction enzymes.

    result of the chemical or proteolytic modification of enzyme specificity by the companies that sell restriction enzymes.

    due to the wide range of specificity observed in naturally occurring restriction enzymes.

    ©1999 Attotron Biosensor Corporation
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