Download Restriction Enzymes

Ch 9-1 & 9-2
DNA Identification
• The repeating sequences in noncoding DNA vary
between individuals and thus can be used to identify
an individual.
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Steps in DNA Identification
1. Copying DNA
– To identify a DNA sample, scientists isolate the
DNA and copy it using the Polymerase Chain
Reaction (PCR)
– Millions of copies are made in just a few hours
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Polymerase Chain Reaction
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Steps in DNA Identification
2. Cutting DNA
– The DNA is then cut into fragments using
restriction enzymes
– Restriction enzymes recognize and cut specific
nucleotide sequences called a restriction site.
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Restriction Enzymes Cut DNA
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Steps in DNA Identification
3. Sorting DNA by Size
– The fragments are separated by size using gel
electrophoresis
– A positive electrode is attached to one side of the
gel (a thin slab of hard gelatin)
– A negative electrode is attached to the other side
– An electric current is sent through the gel and the
DNA (which is slightly negative) moves towards
the positive side
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Steps in DNA Identification
3. Sorting DNA by Size
– There are pores in the gel for the DNA to move
through
– Large pieces of DNA stop sooner (closer to the
negative end)
– Small pieces of DNA move farther (closer to the
positive end)
– The resulting pattern of bands is called a DNA
fingerprint
– a Restriction map shows the lengths of the bands
produced in the gel
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Gel Electrophoresis
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