DNA Technology
Gel Electrophoresis is a method by which the bases of DNA can be
separated. Each DNA base has its own unique molecular weight and will
move through an electrophoresis gel at a different rate. Because of the
negative charge on DNA, bases migrate through a gel oriented between
negative and positive terminals of a gel electrophoresis chamber.
DNA sequencing is the process of identifying the order of nitrogen bases
within a DNA macromolecule. It begins with cutting the chromosome using
restriction enzymes, and making many copies. The strands are separated
and the end of one specific strand is labeled with a radioactive probe. The
multiple copies of this strand are divided into equal quantities and placed in
four test tubes, each of which contains a different chemical is such that it
does not destroy the given nitrogen base each and every place it occurs on
the DNA strand.
Each chemical treatment produces DNA segments of different lengths. The
segments are then sorted by size and charge in a gel electrophoresis. The
segments with radioactive labels will show up on the X ray and can be “read”
to determine the sequence of nucleotides in the gene under study. From this
sequence, a scientist can determine the type of protein that would be
assembled by information from a gene.
Materials
 Photocopy of strands of DNA
 Scissors
 Meter Stick
 Large poster board
 Glue
 Marker
ACGGGACTACCAT
3. The numbers represent the relative distance traveled by the
segments, with “1” being the shortest distance. The smaller the
segment, the longer the distance it migrates. The DNA sequence is
read from the bottom of the X ray to the top, that is from the
smallest segment of the DNA strand to the largest. Read and record
the DNA sequence shown in figure 1. Write the letter sequence of
the bases.
Figure 1
G
A
T
C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Figure 1 – DNA sequence
Procedure
1. Look at the picture of the gel electrophoresis sample in figure 1 on
the next page. Each letter at the top represents one of the four bases
in a nucleotide of a DNA molecule. The marks under each of the
bases represent segments of DNA that migrated through the gel.
2. The radioactive probe attached to the segments “burn” these marks
into the X ray film when it is exposed to the gel.
radioactive probe
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Modeling DNA Sequencing
1. Students should construct a gel electrophoresis diagram like the one
shown below using poster board.
G
A
T
C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
2. Each group should receive 4 different colored sheets of DNA
strands. One sheet representing G, one sheet representing T, and so
on.
3. Cut out the strands and place the 6 strands and place in 4 separate
groups.
4. Take the first set of 6 strands for the letter “G”. Hold the end with
the probe. Starting on the other end of the strand find the first letter
G and make a diagonal cut across it.
Keep the end with the probe attached and throw away the other
piece.
5. Take the second strand and hold it by the probe. Starting on the
other end of the strand, find the second letter G. Make a diagonal cut
across the strand. This strand will be shorter than the first one.
Again keep the end with the probe and throw away the other end.
6. Repeat this procedure for all six strands of “G”. The strand will be
smaller and smaller.
7. Set this pile aside and move to the next letter.
8. Repeat procedure 3-7 for all the bases, A, T, and C.
9. Arrange the pieces from the smallest to the largest. Glue them into
the correct lane on the poster board.
10. Read your DNA gel electrophoresis sample. Write the base
sequence. _______________________________________________
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11. Now transcribe the DNA sample into mRNA using the base pairs AU and C-G.______________________________________________
_______________________________________________________
12. Use the chart below to find the names of amino acids coded for by
mRNA. This is the sequence of amino acids that make up this
protein._________________________________________________
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