Question

The “TOP” of the gel depicted below is where the 4 separate reactions were loaded for sequence determination. Which of the following is true regarding the image below?

: TOP ddTTP ddCTP ddATP ddGTP : BOTTOM

a. The largest/longest nucleotide chains are at the top of the image

b. The largest/longest nucleotide chains are at the bottom of the image

c. A negatively charged electrode will be placed at the “BOTTOM” to run the DNA through the ge

d. The 5’ end of each DNA chain contains a ddNTP

e. The 3’ end of each DNA chain (contained in the bands in the image) contains a ddNTP

Answer 1

In gel electrophoresis separation is based on the size. Longer the size of DNA least distance it will migrate in the gel. Since DNA is negatively charge it will move towards positive electrodes. DNA is moving from top to bottom means the electrode in the bottom is positive charge. At the 5' end of every fragment there is only unlabeled primer. At 3' end when the ddNTPs get incarcerated the elongation of chain get terminated. As a result of this every strand at 3' end contains a ddNTP.

So option A and option E are correct.