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__ and __rely on the use of enzymes that cut DNA molecule at a limited number of specific locations. These enzymes, called __ or __, were discovered in the late 1960s by researchers studying bacteria.
- Gene cloning and genetic engineering
- restriction endonucleases, or restriction enzymes
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How do restriction enzymes protect the bacteria?
by cutting up foreign DNA from other organisms or phages.
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Each __is very specific, recognizing a particular short DNA sequence, or __, and cutting both DNA strands at precise points within this __.
The DNA of a bacterial cell is protected from the cell’s own restriction enzymes by the addition of __groups to adenines or cytosines within the sequences recognized by the enzymes.
- restriction enzyme
- restriction site x2
- methyl
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Most __are symmetrical, same on both strands when read in the 5->3direction.
Most __recognize sequences containing four to eight nucleotides.
Because any sequence this short usually occurs (by chance) many times in a long DNA molecule, a restriction enzyme will make many cuts in a DNA molecule, yielding a set of __.
- restriction sites
- restriction enzymes
- restriction fragments
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All copies of a particular DNA molecule always yield the same set of __when exposed to the same restriction enzyme. In other words, a restriction enzyme cuts a DNA molecule in a reproducible way.
restriction fragments
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The most useful restriction enzymes cleave the __ in the two DNA strands in a staggered manner.
The resulting double-stranded restriction fragments have at least one single- stranded end, called a __.
These short extensions can form hydrogen-bonded base pairs with complementary sticky ends on any other DNA molecules cut with the same enzyme.
- sugar- phosphate backbones
- sticky end
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The associations formed in this way are only temporary but can be made permanent by the enzyme __.
DNA ligase
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