What is Semi-Log Graph
paper…. And WHY do I need
to know?
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DNA can be cut, using
RESTRICTION ENZYMES… into
segments of differing lengths.
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After DNA is separated on an
agarose gel by electrophoresis,
the migration of fragments of
known size can be compared to
that of fragments of unknown
size.
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• Suppose we
have digested
DNA from two
viruses ~ both
with Hind III,
• And
electrophoresed
the DNA from
both on an
agarose gel
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• Electrophoresing
the DNA on an
agarose gel ~~
causes the
migration of the
fragments.
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• After running the gel
~ you measure the
distance the DNA
migrated.
Table 1. Restriction enzyme analysis of λ and UPCFV DNA
λ Virus
DNA Hind III digest
Size (kb)
Distance (mm)
migrated
23.1
9.42
6.56
4.36
2.32
2.03
0.56
3
14
18.5
23.5
32.
34
50
U.P. Cabin Fever Virus (UPCFV)
DNA Hind III digest
Size
?
?
?
?
Distance (mm)
migrated
5
12
15
27
In order to determine the sizes of the U.P. Cabin
Fever Virus DNA, you will make a standard
curve for the known
Lamda DNA
• YUK! This does not
show a linear
relationship between
the fragment size
and distance
migrated… down
towards the right
side of the graph, it
would be difficult
to determine size…
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Size of fragment
• A logarithmic graph, basically takes an
EXPONENTIAL graph and changes it to a LINEAR
one … but using funky graph paper & by using the
log function. (log function is the inverse of an
exponential function)
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Size of fragment
• When a
curve is not
straight.. It
can be made
straight with
logarithms.
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migration
Scientists use logarithmic
graph paper to manage
large amounts of data easily
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• And when you
are talking kilo
base pairs….
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And DNA…. You
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LARGE amount
of data
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See the funky graph paper?
The axis with
the
logarithmic
info runs in
cycles…
The cycles differ by
a factor of 10
btw, this is an
example of 6 cycle
graph paper
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See the funky graph paper?
One of the
virtues of
semilogarithmic
plots is their
ability to show
a very wide
range of
values.