Gel Electrophoresis Basics Worksheet
1. Evaluate the following statements. Rewrite them so that they are correct if
necessary.
a) Each band in a DNA electrophoresis gel is made up of one molecule of DNA.
b) Gel electrophoresis can tell you the sequence of a particular DNA fragment.
c) You can see DNA on a gel because DNA is naturally fluorescent.
d) DNA moves through a gel because it is positively charged and is attracted to the
negative electrode.
e) The speed at which DNA moves through a gel is directly related to its charge.
f) An electrophoresis gel used for DNA is usually made from gelatin which is a protein
obtained from seaweed.
g) When visualizing your gel, you can tell the size of the DNA fragments by seeing how
wide each band is.
h) A gel is placed in a liquid called running buffer because it is an insulator and will
protect the user from electric shock.
The gel to the right contains DNA ladder in the first lane,
followed by four DNA samples in lanes two through five.
The DNA ladder has 10 bands that are each separated by
100 base pairs from lengths 100-1000; it also has bands at
1200 base pairs and 1500 base pairs
2. Which DNA fragment, A, B, C, D, E, or F, is the largest?
Justify your answer.
Fragment E is the larger amongst all fragments shown in the figure since as the previous
excises explain the shorter fragments move or transport faster and fragment E is the last
amongst all, the other fragments have traveled farther from the starting point than
fragment E due to their shorter size. Also at the corner or left side of the image we have a
kind figure that shows the lengths of the fragments and according to it fragment E is the
largest.
3. Which two DNA fragments are the same size? How do you
know this?
Fragments B and F are the same length because they are traveling at an equal rate of
speed and that can only be possible if both have the same size because the size of the
DNA fragments determine the speed at which they traveled and both are moving side by
side which can only be possible if they have the same size.
4. Which lane of the gel, 2, 3, 4, or 5, has a DNA fragment that is about 700 base pairs?
Lane of gel 4 has the fragment C which according to the measurements at the left side
measure 700, since is two sticks above 500 and each stick represent 100.
5. Which DNA fragment, B, C, D, or E is about the same size as the lengths of the fragment
A and fragment F added together?
Fragment A is in between the stick of 500 and 600 meaning it measure 550, while
fragment F measures 300. Added together they measure 850. The closest fragment to 850
is fragment E which measures 900 which is only 50 over the measurement of the
measurement of both fragments, meaning fragment E is the one with the closest
measurement.
Actual gels don’t have labels. Here, the labels have been
removed, but the ladder remains the same as in the
previous example.
6. On the gel to the right, write the approximate size of each DNA
fragment. Write the sizes next to each appropriate band.
I will name the fragments from 1 to 7 based on their positions the nearest to the bottom
of the image is one and so on. The first stick on the left side is the one with represents 100
and since fragment 1 is underneath it we can assume it has a size of 50. Fragments 2 and 3
are in between the sticks which represent 200 and 300 meaning both measure 250.
Fragment 4 is in between the sticks of 450 and 500 meaning it measures 450. Fragment 5
measures 600 and fragment 6 measures 700. Fragment 7 is just a little bit lower than the
stick which represent 900 meaning it measures 890.
7. Imagine that you have a sample of DNA that contains a
single, specific DNA sequence. Before you run your gel, you split
your sample into two tubes. You run the DNA from the first tube
in lane two of your gel. You take the other tube and use an enzyme
called a restriction enzyme that cuts the DNA into two pieces at a
specific point in the sequence. You then run this sample that was
cut on the gel.
Which of the next three lanes (lane 3, 4, or 5) could be the same
sample from lane two after it was cut into two pieces?
Lane 3 is the same sample than lane 2 because lane 2 fragment measure 700 and the
fragments in lane 3 when added measure 700 as well.
Use the image of a gel on the right to draw where you think
you would see the bands described below.
8. You run the following samples on a gel:
Lane 1: DNA ladder (Drawn for you)
Lane 2: a fragment of DNA that is 375 base pairs long
Lane 3: three fragments of DNA, one that is 150 base pairs,
one that is 400 base pairs and a third that is 780 base pairs
Lane 4: a 1,200-base pair fragment that has been cut in two
by a restriction enzyme at base pair number 370
Lane 5: a 50-base pair fragment of DNA and a 2,400 base pair
fragment of DNA
