Question
A protein with a molecular weight of 100 kD is subjected to SDS PAGE electrophoresis. The SDS PAGE electrophoresis pattern shows two widely separated bands of 20kD and 30kD after the addition of Mercaptoethanol. The true statement regarding this will be-
A. The protein has undergone complete lysis
B. The protein is a monomer of 20 kD and 30kD protein
C. The protein is a dimer of two 20kD and 30kD proteins
D. The protein is a tetramer of 20kd and 30kD proteins
Show Answer
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Correct Answer » C
Explanation
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Ans.C
Most widely used method for determination of purity and molecular weight of proteins is SDS- PAGE i.e. polyacrylamide gel electrophoresis in the presence of anionic detergent sodium dodecyl sulfate
SDS PAGE gel electrophoresis separates proteins on the basis of their relative molecular weight alone. Since the results of SDS PAGE electrophoresis show two bands only, the protein that underwent SDS-PAGE is composed of polypeptides with two different molecular weights (One of 20 KD and the other of 30kD). If the protein in question was a monomer its molecular weight should have been 50kD. Since the protein has a molecular weight of 100kD, the protein is likely to be a dimmer of two 20 kD proteins (Which form one band) and two 30 kD proteins (Which form the other band).
