This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Hybridization of DNA and RNA”.
1. Which of the following does not affect the formation of hybrid DNA?
a) Ionic strength
b) Pressure
c) Temperature
d) Homologous DNA
View Answer
Explanation: Hybrid molecules are formed when homologous, denatured DNAs from two different sources are mixed with each other. This occurs due to the presence of complementary bases and under appropriate ionic strength and temperature.
2. Which of the following is not termed as hybridization?
a) DNA and cDNA
b) DNA and mRNA
c) DNA from different species
d) DNA from male and female of same species
View Answer
Explanation: The process of base – pairing between complementary DNA strands from different sources of species is termed as hybridization. Thus DNA from male and female of same species is not known as hybridization.
3. What is a probe?
a) Chemically synthesized DNA
b) Purified DNA
c) Fragmented DNA duplex
d) Either purified or synthesized single stranded DNA
View Answer
Explanation: A probe is a known DNA oligonucleotide used to search for specific DNA sequences containing its complementary sequence. These probes can be both, purified DNA or chemically synthesized single stranded DNA.
4. Why is a probe labeled?
a) Improve visibility
b) Improve stability
c) Improve location identification
d) Improve binding capability
View Answer
Explanation: The probe is labeled because to improve its location identification. This means the probe DNA must be labeled so that it can be readily located once it has found its target sequence.
5. In how many ways a DNA can be labeled?
a) 2
b) 3
c) 4
d) 5
View Answer
Explanation: There are two basic methods for DNA labeling. The first involves the synthesis of the probe DNA in the presence of a labeled precursor. The other involves adding a label to the end of an intact DNA molecule.
6. What is the function of polynucleotide kinase?
a) Addition of γ – phosphate at 3’ – OH
b) Addition of γ – phosphate at 5’ – OH
c) Removal of γ – phosphate at 3’ – OH
d) Removal of γ – phosphate at 5’ – OH
View Answer
Explanation: The enzyme polynucleotide kinase is known to add γ – phosphate at 5’ – OH end of the DNA strand. This reaction occurs at the cost of an ATP molecule which id hydrolyzed to extract energy and a phosphate.
7. Fluorescent labeling is an important phenomenon in case of hybridization and manipulations in molecular biology.
a) True
b) False
View Answer
Explanation: DNA labeled with fluorescent precursors can be easily detected by irradiating the DNA sample with appropriate wavelength of UV light. The results can be monitored by visualizing the longer wavelength light emitted by the labeled DNA. This is thus very important in localization of probes and thus identifying the location of the target DNAs.
8. Radiolabelling is generally brought about by addition of radioactive phosphorus.
a) True
b) False
View Answer
Explanation: Radioactively labeled precursors typically have radioactive 32P or 35S incorporated into α – phosphate of one of the four nucleotides. Radioactive DNA can be detected by exposing the sample of interest to X – ray film or by photomultipliers that emit light in response to excitation by the β – particles emitted by from 32P and 35S.
9. During electrophoresis denaturation of the double stranded DNA is brought about by __________
a) Treatment with alkali
b) Application of current
c) Treatment with EtBr
d) Application of heat
View Answer
Explanation: During electrophoresis denaturation of the double stranded DNA is brought about by its treatment with alkali. This step is done once the sample is separated by electrophoresis and taken up in the nitrocellulose membrane.
10. In case of northern blotting the hybridization occurs between two RNA molecules.
a) True
b) False
View Answer
Explanation: The electrophoretically separated RNAs are transferred into a positively charged membrane. Then probe of radioactive DNA of choice is used thus in case of northern blotting the hybridization occurs between a DNA and a RNA molecule.
11. Northern blotting is performed for ____________
a) Determining the size of DNA
b) Determining the size of RNA
c) Quantification of RNA
d) Sequencing of RNA
View Answer
Explanation: Northern blotting is performed by an experimenter to ascertain the amount of a particular mRNA present in the sample rather than its size. This measure is a reflection of the level of expression of the gene that encodes it.
12. The process by which a probe is used to screen a library is known as ___________
a) Hybridization
b) Southern blotting
c) Colony hybridization
d) Western blotting
View Answer
Explanation: The process by which a labeled DNA probe is used to screen a library is known as colony hybridization. This process uses the technique of replica plating.
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