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Question
A mixture of DNA fragments from the same source, after amplification was loaded into wells of two different gels, A and B. The magnified image of the agarose gel after gel electrophoresis has been given below with the possible marker values given aside.
Select the appropriate statement(s) among the following.
I. Gel A has greater agarose concentration than gel B
II. Gel A has lesser agarose concentration than gel B
III. The pore size of gel A is smaller than that of gel B
IV. The pore size of gel B is smaller than that of gel A
A mixture of DNA fragments from the same source, after amplification was loaded into wells of two different gels, A and B. The magnified image of the agarose gel after gel electrophoresis has been given below with the possible marker values given aside.
Select the appropriate statement(s) among the following.
I. Gel A has greater agarose concentration than gel B
II. Gel A has lesser agarose concentration than gel B
III. The pore size of gel A is smaller than that of gel B
IV. The pore size of gel B is smaller than that of gel A
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Solution
The correct option is D II and IV
Agarose gel electrophoresis is a technique that separates charged molecules (here, negatively charged DNA) of different sizes under the influence of an electric field. DNA fragments migrate towards the anode under the influence of the electric field. The rate of migration is affected by the shape and size of the molecules, strength of electric field as well as concentration of agarose.
The concentration of agarose determines the pore size of the gel. The pores present in the agarose gel create a sieving effect. This helps in the separation of DNA fragments based on their size. A gel with higher agarose concentration would have greater cross linkage and decreased pore size. This will allow the molecules to cover less distance than the gel with greater pore size.
In this case, the DNA sample loaded in both the gels were the same. The DNA fragments present in the sample mixture are migrating a longer distance from the well in gel A than in gel B. This means that the composition of the two gels are different. Gel A must be containing lesser agarose concentration than gel B. This must have caused greater cross-linkage in gel B compared to gel A. This must have resulted in greater pore size in gel A as compared to gel B. Hence, the same piece of DNA fragment must have migrated a longer distance in gel A compared to that in gel B, provided all other reaction conditions are kept constant.
Agarose gel electrophoresis is a technique that separates charged molecules (here, negatively charged DNA) of different sizes under the influence of an electric field. DNA fragments migrate towards the anode under the influence of the electric field. The rate of migration is affected by the shape and size of the molecules, strength of electric field as well as concentration of agarose.
The concentration of agarose determines the pore size of the gel. The pores present in the agarose gel create a sieving effect. This helps in the separation of DNA fragments based on their size. A gel with higher agarose concentration would have greater cross linkage and decreased pore size. This will allow the molecules to cover less distance than the gel with greater pore size.
In this case, the DNA sample loaded in both the gels were the same. The DNA fragments present in the sample mixture are migrating a longer distance from the well in gel A than in gel B. This means that the composition of the two gels are different. Gel A must be containing lesser agarose concentration than gel B. This must have caused greater cross-linkage in gel B compared to gel A. This must have resulted in greater pore size in gel A as compared to gel B. Hence, the same piece of DNA fragment must have migrated a longer distance in gel A compared to that in gel B, provided all other reaction conditions are kept constant.
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