This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Separation of DNA Fragments by Electrophoresis”.
1. Which of the following cannot be used for the separation of nucleic acids?
a) SDS – PAGE
c) Northern blotting
Explanation: Sodium dodecyl sulphate is a detergent, often used in biochemical preparations, binds to proteins and causes them to form a rod like structure. Most proteins bind SDS in the same ratio (1.4g per g of protein). Thus, the electrophoresis of proteins in an SDS – containing polyacrylamide gel separates them in order of their molecular masses. It is not known to have the similar effect on nucleic acids.
2. The polymerization of the gel used in PAGE occurs between polyacrylamide and ____________
a) N, N – acrylamide
c) N – methyleneacrylamide
d) N, N – methylene bisacrylamide
Explanation: In PAGE, polyacrylamide gel electrophoresis, gel is made by free radical by polymerizing the monomers together. The two major monomers between which the polymerization occurs are polyacrylamide and N, N – methylene bisacrylamide in the buffer of choice.
3. If DNA is digested by endonucleases in four sites giving rise to fragments of which two are equal in length how many bands would be seen after electrophoresis?
Explanation: Digestion at four sites gives rise to five fragments. Two fragments are of same size thus they will form a single band. Therefore only four bands is observed.
4. The fluorescent dye such Ethidium is used for visualizing DNA. How do ethidium binds to DNA?
a) Stacked between histone molecules
b) Binds to the nucleotide base
c) Intercalated between the stacked bases
d) Binds to the phosphodiester backbone
Explanation: Ethidium is intercalated between the stacked bases. This increases the spacing of successive base pairs, distorts the regular sugar phosphate backbone and decreases the twist of the helix.
5. Pulse field gel electrophoresis separates DNA molecules of size ___________
a) 10 – 20 bp
b) 20 – 30 Kb
c) 30 – 50 Kb
d) 40 – 50 bp
Explanation: DNA molecules ranging from 30 – 50 kb migrate in a snake like manner thus, cannot be readily be resolved. These long DNAs can be separated by changing the orientation of the electric field. This process of separation is known as PFGE.
6. Which of the following will migrate faster? The condition is the molecular weight of the following is equal.
a) Supercoiled circular DNA
b) Nicked circular DNA
c) Single stranded DNA
d) Double stranded DNA
Explanation: Supercoiled circular DNA has a less effective volume than the others. Thus, it migrates more rapidly when subjected to electrophoresis due to its compact structure.
7. Agarose can be extracted from which of the following?
a) Gracilaria esculentus
b) Lycazusican esculentum
c) Ficum benghalensis
d) Agrostis stolonifera
Explanation: As we know agarose is extracted from seaweeds. Precisely two types of species are used for the extraction; they are the Gracilaria esculentus and Gelidium nudifrons.
8. Electrophoresis cannot be used to separate _______________
c) Amino acid
Explanation: DNA, RNA and protein can be separated by the by the method of electrophoresis as it can be separate charged molecules. Amino acids are generally separated by the process of chromatography.
9. Which of the following is not a character of polyacrylamide gel?
b) Ionic strength
c) Stable over a wide range of pH
d) Separate upto a few 100 bp of DNA
Explanation: The pore size of polyacrylamide gel is very small due to high resolution power. Thus, it can separate DNA fragments upto a few 100 base pairs only.
10. Pulse field gel electrophoresis was developed by ____________
a) Collins and John
b) Kary Mullis
c) Patrick O’ Farrell
d) Schwartz and Cantor
Explanation: PFGE was developed by Schwartz and Cantor in 1984. This mechanism was developed to separate molecules as long as 10 Mb in an agarose gel.
Sanfoundry Global Education & Learning Series – Molecular Biology.
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