Chapter 13, Problem 2STP

Solution

Introduction:

Gel electrophoresis refers to technique by which macromolecules such as DNA, RNA and proteins are separated according to their size and charge. This technique is used in clinical chemistry, biochemistry and molecular biology to separate proteins by charge and to separate DNA and RNA fragments by length.

Gel electrophoresis involves an electrical field and the field is applied in such a manner that one end of the gel has a positive charge and the other end has a negative charge.  

The nucleic acid molecules are separated by using gel electrophoresis that is by applying an electric current to move the negatively charged molecules through a matrix of agarose gel. As DNA carry negative charge, the short molecules move faster and migrate farther as compared to longer molecules because shorter molecules move more easily through the pores of the gel. This phenomenon is called sieving.

The correct option isA, Band A.

Correct answer:

A. Band A has covered the most distance and migrated farther as compared to other molecules, so it is the one which contains smallest DNA fragment.

Explanation for incorrect answers:

B. Band B has covered a little distance and it is nearby the gel chamber so it contains large DNA fragments.

C. Band C has not covered any distance and is closest to the gel chamber hence it contains the largest DNA fragments.

D. Band D has covered some distance that is more than band B but is less than band A so it can be concluded that it contain DNA fragments larger than band A but smaller than band C.