Download Human Genome

14.3
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 Scientists can read the base sequence in DNA from
any cell by using tools that cut, separate, and
replicate DNA base by base.
 DNA molecules are too large to be analyzed, so they have to
be cut into smaller pieces.
 Bacteria produce enzymes that do this
 Restriction enzymes: highly specific substances that cut
even the largest DNA molecule into smaller pieces.
 These smaller pieces are called restriction fragments.
 There are hundreds of known restriction enzymes; each cuts
DNA at a different spot.
 Used once DNA has been cut
 Gel electrophoresis: technique used to
separate & analyze the fragments
 Mixture of DNA is placed in wells on a slice
of gelatin
 Electric voltage applied
 Electricity moves fragments across the gel
 Short fragments move faster (1-2 hours)
 Fragments are separated
 They appear as a band on the gel
 Reading = sequencing DNA
 Single-stranded DNA fragments are placed in a test tube with
DNA polymerase (enzyme that copies DNA) along with the
four bases A, T, C, G.
 Unknown strand is used as a template for the new
complementary strand
 Each time a dye colored nucleotide is added, DNA replication
stops
 Results in color coded DNA fragments of different lengths
 When gel electrophoresis is used to separate the fragments,
we can “read” the DNA sequence directly from the gel
 A 13-year international effort with the main goals of
sequencing all 3 billion base pairs of human DNA and
identifying all human genes.