Question

What is the criterion for DNA fragments movement on agarose gel during gel electrophoresis?
A. Negatively charged fragments do not move.
B. The larger the fragment size, the farther it moves.
C. The smaller the fragment size, the farther it moves.
D. Positively charged fragments move to the farther end.

Answer 1

Hint:- Gel electrophoresis is a method of separation as well as analysis of different types of macromolecules such as DNA, RNA and proteins. This method separates the fragments of nucleic acid and protein on the basis of their size and charge. It is used to separate a mixture of DNA and RNA fragments on the basis of size and charge.

Complete step-by-step solution:-
Gel electrophoresis is the method which allows for selection of desired macro molecules among the mixture of different nucleic molecules. In this process molecules are separated on the basis of their size and charge. It is a useful method to separate DNA for analytic purposes after amplification of DNA by PCR method. In this process using an electric field molecules are made to pass through a medium of gel. The gel is generally agarose or polyacrylamide. The electric field contains a negative charge end and the charge pushes the molecule through the gel. The other end of the electric field contains positive charge and pulls the molecule through the gel. The media containing the molecules to be separated are subjected into the well in the gel material. The gel is now placed into an electrophoresis chamber and it is connected to a power source. The power source creates an electric field which causes the larger molecule to move slowly through the gel while shorter molecules move faster.
The gel used is agarose which forms a solid but porous matrix. Agarose is composed of long unbranched chains of uncharged carbohydrates without cross links. This creates a gel with large pores which is suitable for the separation of macromolecules. The DNA containing media when exposed to the agarose gel electrophoresis causes the migration of DNA molecules towards the positive end. This occurs due to the fact that DNA is negatively charged. As the size of DNA is small it travels much faster and further than other molecules.
Positively charged fragments will be attracted at the negative end of the electrophoresis and the movement of the molecules depends on the size and not on the charge.
Negatively charged fragments will move to the positive charge due to attraction of charges.
The larger the fragment size will cause the fragment to move slowly than the other molecules.
Therefore, the correct option is option C.

Note:- Gel electrophoresis is the mechanism of separation of macromolecule and fragment on the basis of charge and size. It consists of a positive end and a negative end and molecules are separated after application of an electric source. The molecules or fragments such as the DNA fragments gets separated on the basis of their size due to the sieving effect of the agarose gel