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Inquiry Questions

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Self Test

1). Cutting certain genes out of molecules of DNA requires the use of special
    a). degrading nucleases.
    b). restriction endonucleases.
    c). eukaryotic enzymes.
    d). viral enzymes.
Answer: b

2). Which of the following cannot be used as a vector?
    a). phage
    b). plasmid
    c). bacterium
    d). All can be used as vectors.
Answer: c

3). In Cohen and Boyer's recombinant DNA experiments, restriction endonucleases were used to
    a). isolate fragments of cloned bacterial plasmids.
    b). isolate fragments of frog DNA that contained an rRNA gene.
    c). cleave the bacterial plasmid.
    d). All of these are correct.
Answer: d

4). A DNA library is
    a). a general collection of all genes sequenced thus far.
    b). a collection of DNA fragments that make up the entire genome of a particular organism.
    c). a DNA fragment inserted into a vector.
    d). all DNA fragments identified with a probe.
Answer: b

5). A probe is used in which stage of genetic engineering?
    a). cleaving DNA
    b). recombining DNA
    c). cloning
    d). screening
Answer: d

6). The enzyme used in the polymerase chain reaction is
    a). restriction endonuclease.
    b). reverse transcriptase.
    c). DNA polymerase.
    d). RNA polymerase.
Answer: c

7). A method used to distinguish DNA of one individual from another is
    a). polymerase chain reaction.
    b). cDNA.
    c). reverse transcriptase.
    d). restriction fragment length polymorphism.
Answer: d

8). Inserting a gene encoding a pathogenic microbe's surface protein into a harmless virus produces a
    a). piggyback vaccine.
    b). virulent virus.
    c). active disease-causing pathogen.
    d). pharmaceutical human protein.
Answer: a

9). Although the Ti plasmid has revolutionized plant genetic engineering, one limitation of its use is that it
    a). cannot infect broadleaf plants.
    b). cannot be used on fruit-bearing plants.
    c). cannot transmit prokaryotic genes.
    d). does not infect cereal plants such as corn and rice.
Answer: d

10). Which of the following is not an application of genetic engineering in plants?
    a). nitrogen fixation
    b). DNA vaccines
    c). resistance to glyphosate
    d). production of insecticidal proteins in plants
Answer: b

Test Your Visual Understanding

1). What process is illustrated in this figure? Where in the cell would you look to find the primary RNA transcript, and where would you look to find the mature mRNA transcript?
Answer: The process illustrated is the production of complementary DNA or cDNA. The primary RNA transcript is present in the nucleus of the cell. The mature mRNA transcript is present in the cytoplasm of the cell. The primary RNA transcript contains introns that are spliced out by enzymes present in the nucleus and from there, the mature mRNA transcript moves out of the nucleus into the cytoplasm.

2). When might researchers use this process? That is, what would they be trying to accomplish?
Answer: Researchers use the production of cDNAs when they require the DNA that codes for the final protein product, which is encoded by the mature mRNA transcript. This is needed when using bacteria to mass produce a eukaryotic protein. If a copy of the DNA for a particular protein was placed in a bacterium, all of the introns in addition to the exons would be transcribed and translated and the protein would not be functional. It is necessary to use the mature mRNA to make the cDNA that can then be inserted into the bacterium so that the functional protein product is made.

Apply Your Knowledge

1). The human genome has about 3 billion base-pairs. Assume you wanted to clone the entire human genome using various vectors, but there is a limit to the size of a DNA fragment that can be inserted in a vector. Following is a list of vectors along with their size limit of DNA fragment. Calculate how many vectors of each type would be needed to generate a library of the human genome.
    a). bacterial plasmid-18 kilo base-pairs
    b). phages-25 kilo base-pairs
    c). YACs-250 kilo base-pairs
1a). The human genome is 3 billion base-pairs or 3 x 109 bp and so the number of bacterial plasmids needed would be:
3 x 109 bp / 18,000 bp = 166,667 plasmids
1b). The number of phages needed would be:
3 x 109 bp / 25,000 = 120,000 phages
1c). The number of YACs needed would be:
3 x 109 bp / 250,000 = 12,000 YACs

2). A major focus of genetic engineering has been on attempting to produce large quantities of scarce human proteins by placing the appropriate genes into bacteria and thus turning the bacteria into protein production machines. Human insulin and many other proteins are produced this way. However, this approach does not work for producing human hemoglobin. Even if the proper clone is identified, the fragments containing the hemoglobin genes are successfully incorporated into bacterial plasmids, and the bacteria are infected with the plasmids, no hemoglobin is produced by the bacteria. Why doesn't this experiment work?
Answer: Hemoglobin is a complex protein actually made of four polypeptide chains that are held together in a quaternary structure. There are also four heme groups (iron-containing groups) that are associated with each polypeptide chain. The complexity of this molecule may preclude its synthesis by a bacterial cell. Other genes are most likely involved in the formation of the tertiary and quaternary structures and involved in the incorporation of the heme groups into the polypeptides. A bacterial cell may be able to translate the gene into a polypeptide but the further complexity of the molecule probably restricts its synthesis by bacteria.

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