____ 4.By mistake, DNA fragments were loaded onto a gel using a buffer with a pH so low that all the phosphate groups of the DNA nucleotides were protonated (i.e., had H+ ions added to them.) Subsequent electrophoresis failed to separate the fragments. This was because [I OBJ:6.1]

Question

____ 4.By mistake, DNA fragments were loaded onto a gel using a buffer with a pH so low that all the phosphate groups of the DNA nucleotides were protonated (i.e., had H+ ions added to them.) Subsequent electrophoresis failed to separate the fragments. This was because [I OBJ:6.1]

a. the voltage difference across the gel was inadequate
b. the double-stranded fragments became single-stranded and all migrated very swiftly to the positive pole
c. the fragments joined together into one huge molecule
d. the fragments had very little charge, and thus were not attracted to the positive pole
e. "the fragments became circular"

Answer 1

The correct answer to the question is (d) the fragments had very little charge, and thus were not attracted to the positive pole.

To understand why this is the correct answer, we need to consider the process of electrophoresis and how it works. Electrophoresis is a technique used to separate and analyze DNA fragments based on their size and charge. It involves applying an electric field to a gel matrix containing the DNA fragments.

During electrophoresis, the negatively charged DNA fragments move towards the positive pole (anode) due to the electric field. The size of the DNA fragments determines how quickly they move through the gel. Smaller fragments can move more quickly and migrate further, while larger fragments move slower and migrate a shorter distance.

In the given scenario, the buffer used for electrophoresis had a pH so low that all the phosphate groups on the DNA nucleotides were protonated, meaning they had H+ ions added to them. This protonation of the phosphate groups reduces the overall negative charge of the DNA fragments.

Since the DNA fragments had very little negative charge due to the protonation of phosphate groups, they would not be attracted to the positive pole during electrophoresis. As a result, the fragments would fail to separate as they would not migrate towards the anode.

Therefore, the correct answer is (d) the fragments had very little charge, and thus were not attracted to the positive pole.