what is semi-log graph paper…. and why do i need to know?
Post on 03-Jan-2016
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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.
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.
• 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.
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Table 1. Restriction enzyme analysis of λ and UPCFV DNA
λ Virus U.P. Cabin Fever Virus (UPCFV)
DNA Hind III digest DNA Hind III digest
Size (kb) Distance (mm) Size Distance (mm)migrated migrated
23.1 3 ? 5 9.42 14 ? 12 6.56 18.5 ? 15 4.36 23.5 ? 27 2.32 32. 2.03 34 0.56 50
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
Leng
th m
igra
ted
• 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
Leng
th m
igra
ted
• When a curve is not straight.. It can be made straight with logarithms.
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migration
Log
of f
ragm
ent
leng
th
Scientists use logarithmic graph paper to manage
large amounts of data easily
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• And when you are talking kilo base pairs…. And DNA….
You are discussing a
LARGE amount of data
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Qu
ickTim
e™
and
a d
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pre
sso
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de
d t
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ee t
his
pic
ture
.
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
Qu
ickTim
e™
and
a d
ecom
pre
sso
rare
nee
de
d t
o s
ee t
his
pic
ture
.
See the funky graph paper?
One of the virtues of
semi-logarithmi
c plots is their
ability to show a
very wide range of
values.
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