I. MICROBIAL GENETICS
G. Genetic Recombination in Bacteria
5. Recombinant DNA
Genetic Recombination in Bacteria (def)
Genetic recombination is the transfer of DNA from one organism to another. The transferred donor DNA may then be integrated into the recipient's nucleoid by various mechanisms.
Natural mechanisms of genetic recombination in bacteria include:
a. transformation
b. transduction
c. conjungation
DNA can also be transferred to bacteria by recombinant DNA technology.
Genes in bacteria can also bealtered artificially through recombinant DNA technology. In recombinant DNA technology, discussed later in this unit, endonuclease and ligase enzymes are routinely employed. Restriction endonuclease enzymes (def) are naturally occurring enzymes in bacteria that help protect bacteria from viral attack by cutting up the foreign viral DNA while not harming the bacterium's own DNA. Restriction endonuclease enzymes recognize specific palandromic deoxyribonucleotide base sequences (base sequences that read the same forward and backward on the complementary DNA strands), and then split each DNA strand at a specific site within that sequence. For example, Escherichia coli makes a restriction endonuclease called Eco R1 that recognizes the deoxyribonucleotide base sequence G-A-A-T-T-C and cuts the DNA strand between the G and the A. Since the complementary strand has the sequence CTTAAG, it is also cut between the G and the A (see Fig. 1). This leaves short, complementary, single-stranded sticky ends capable of hydrogen bonding with the complementary sticky ends of DNA fragments cut by the same enzyme, as seen in Fig. 2 through 5. (These same enzymes are used routinely in recombinant DNA technology, as will be discussed later in this unit.) The inserted fragments can then be joined by the enzyme DNA ligase (def).
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