Molecular Biology Questions and Answers – Construction of DNA and RNA Libraries

This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Construction of DNA and RNA Libraries”.

1. How many types of DNA libraries are possible?
a) 1
b) 2
c) 3
d) 4
View Answer

Answer: b
Explanation: There are two types of DNA libraries that can be produced. They are genomic DNA library and cDNA library that is produced from the reverse transcription of the mRNAs produced.

2. In the following type of libraries pick the odd one out.
a) A DNA library
b) B DNA library
c) cDNA library
d) Z DNA library
View Answer

Answer: c
Explanation: cDNA library lacks DNA fragment from the genomic DNA. This type of library is produced by the action of reverse transcriptase on the mRNA molecule to synthesize complementary DNA molecules without the intervening introns.

3. Which enzyme is involved in the synthesis of the DNA over an RNA template?
a) DNA polymerase
b) Reverse transcriptase
c) Klenow fragment
d) RNA polymerase
View Answer

Answer: b
Explanation: Reverse transcriptase is the enzyme that is involved in the reverse transcription of mRNA molecule. Thus it is used to produce the DNA copy from the mRNA transcript to form the cDNA library also known as the RNA library.

4. For the construction of DNA library what is the range of genomic DNA that has to be cloned into the vector?
a) Less than 100 bases
b) 100 to 1000 bases
c) Less than 100 to mega bases
d) Less than 10 bases
View Answer

Answer: c
Explanation: To construct a DNA library the target DNA is digested with a restriction endonuclease. This provides us with the desired range of fragments that can be incorporated within the vector and also the whole genome can be preserved within bacterial cells.

5. Which of the following enzymes is responsible for the digestion of the RNA strand in the RNA-DNA hybrid?
a) RNase A
b) RNase H
c) DNase
d) Exonuclease
View Answer

Answer: b
Explanation: When making a cDNA library the DNA copy is made from an RNA template thus leading to the formation of the RNA-DNA hybrid. Thus for the production of the chimera molecule the RNA template needs to be hydrolysed which is provided by RNase H enzyme whereas RNase A enzyme removes RNA primer from the in case of replicating the lagging strand.
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6. cDNA is synthesized from __________
a) Protein chain
b) tRNA
c) mRNA
d) DNA
View Answer

Answer: c
Explanation: cDNA contains only coding sequences of the genomic DNA. Instead of starting with genomic DNA, mRNA is transcribed into DNA sequences by the action of reverse transcriptase.

7. During storage of DNA fragments for making library, larger fragments are having more chances of getting lost.
a) True
b) False
View Answer

Answer: a
Explanation: During the making of DNA library storing of larger fragments becomes complicated and while replication it might get lost. Thus average insert size taken is less than the insert size capacity of the vector.

8. What is the characteristic of the DNA that is used for the construction of library?
a) Naked DNA
b) Plasmid
c) Plasmid and naked DNA
d) Plasmid is preferred over naked DNA
View Answer

Answer: c
Explanation: Those libraries which are constructed using a plasmid containing cells. Although naked DNA can also be inserted in the plasmid containing cells as the host transforms the naked DNA as per requirement.

9. What is the state of phage cloning vector that is used for the construction of library?
a) Packaged phage
b) Unpackaged phage
c) Packaged and unpackaged phage
d) Packaged and unpackaged phage are used but unpackaged phage is favored
View Answer

Answer: b
Explanation: Packaged phage is the one that contains viral genome but unpackaged phage is the one that does not contain any genetic material. If the phage is devoid of any genetic material it is easier to introduce desired DNA fragment and its integration into the host without the development of any infectious effect. Thus unpackaged phage is favored over packaged phage.

10. Which enzyme is used to avoid ligation of separate DNA?
a) Kinase
b) Phosphatase
c) Endonuclease
d) Ligase
View Answer

Answer: b
Explanation: Phosphatase is used to avoid ligation of separate DNA segments. Phosphatase is used to remove the terminal phosphate groups thus preventing the ligation.

11. Partial digestion is preferred for the fragmentation of DNA.
a) True
b) False
View Answer

Answer: a
Explanation: For the partial digestion all fragments of DNA needs to be represented. Thus partial digestion is preferred over the complete digestion.

12. The ordered steps for the construction of library involves __________

i) Vector preparation
ii) Amplification
iii) Ligation and introduction into the host
iv) Isolation of genomic DNA
v) Fragmentation of DNA

a) iv, v, i, iii, ii
b) v, iv, i, iii, ii
c) i, ii, iii, iv, v
d) ii, iii, iv, v, i
View Answer

Answer: a
Explanation: The order of the steps is:
i) Isolation of genomic DNA
ii) Fragmentation of DNA
iii) Vector preparation
iv) Ligation and introduction into the host
v) Amplification.

13. What is the significance of “c” in cDNA library?
a) Copy DNA
b) Cut DNA
c) Cell DNA
d) Clone DNA
View Answer

Answer: a
Explanation: In cDNA library mRNA sequences are converted into double stranded DNA copies called cDNA. Thus significance of “c” in cDNA library is copy DNA as it is the copy of RNA segment in the form of DNA and not fragmented DNA itself.

14. mRNA can be readily separated from lysed eukaryotic cells adding magnetic beads. What is the sequence of this magnetic bead?
a) Oligo G
b) Oligo A
c) Oligo T
d) Oligo C
View Answer

Answer: c
Explanation: mRNA is used in the construction of cDNA library. The magnetic beads that is used for magnetic separation of mRNA molecules are oligo T sequence.

15. What is the significance of SI nuclease?
a) DNA synthesis
b) Cleavage of hooks
c) Degrades RNA
d) Annealing the primer
View Answer

Answer: b
Explanation: SI nuclease is the enzyme that is used in cDNA library. SI nuclease cleaves the hook which is extended by DNA polymerase I into complementary strand during cloning the cDNA library.

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