DNAAnalysis211S - DNA Analysis and Molecular Medicine 1...

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DNA Analysis and Molecular Medicine - 1 James Watson and Francis Crick opened a new era of genetic research when they submitted a letter to the journal Nature stating they believed they had determined the structure of DNA. We have been discussing the structure and functions of DNA and how mutations affect gene function, with some emphasis on mutations and genetic diseases. During our discussion of genetic diseases, we alluded frequently to the tools of current DNA research that provide us with better analysis of and identification of the DNA sequences that result in genetic diseases and other genetic differences. Before continuing our discussion of gene expression and regulation, we will pause to introduce some of the tools molecular geneticists use to locate and analyze DNA, a field of biology often called DNA (or genetic) technology. We will also look at some examples of how altered DNA causes genetic diseases and discuss ways in which we can treat genetic diseases as we gain more knowledge and skills for analyzing DNA within cells and organisms. Molecular Tools for Locating and Analyzing DNA Critical to any genetic technology process is the set of enzymes that can cut DNA, excise a desired DNA sequence and splice it into a target DNA. Although Barbara McClintock was the first to identify mobile genes that could move from one location and insert into a new location in corn DNA in the 1940's (see later) , it was not until the 1970's that enzymes that could make these cuts were identified in bacteria and first used in DNA research. Bacteria are subject to a number of viruses, which, as we have seen, inject their genetic molecule into the bacterium, where it may incorporate into the host bacterium's genome. Viruses often kill their hosts after they use the host's transcription and translation enzymes to synthesize and assemble new viral DNA and proteins. As a defense mechanism, bacteria have a set of enzymes that recognize and cut specific DNA sequences into small fragments, excising them from the bacterial genome. The bacterium protects itself by altering, by methylation, its own DNA sequences that could be susceptible to the enzymes. These enzymes are called restriction enzymes (or restriction endonucleases) because each different enzyme recognizes just one specific DNA sequence to cut. Restriction enzymes catalyze cutting of both strands of a DNA molecule at very specific DNA base sequences, called recognition sites. At the recognition site, specific nucleotide shapes within the DNA fit the active site of the enzyme. (We shall see in our gene regulation section that transcription factors locate DNA for transcription in a similar fashion.)
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DNA Analysis and Molecular Medicine - 2 Recognition sites are typically 4 - 8 DNA base pairs long, and are often palindromes (regions where the order of nucleotides at one end is the reverse of the sequence at the opposite end). By having complementary cut sites, a restriction enzyme will cut tiny "sticky ends" of
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DNAAnalysis211S - DNA Analysis and Molecular Medicine 1...

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