This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Reverse Transcriptase PCR”.
1. Reverse transcriptase produces DNA from RNA.
a) True
b) False
View Answer
Explanation: Production of DNA from RNA is the reverse process of transcription. Such DNA produce will not be exactly same as its parent gene as it will lack the introns as it is converted from the RNA. This reaction is facilitated by the enzyme reverse transcriptase and the DNA thus formed is known as the complementary DNA or the cDNA.
2. Which of the following serves as the first primer in RT – PCR for eukaryotic RNA?
a) Oligo A
b) Oligo T
c) Oligo G
d) Oligo C
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Explanation: All RNAs have a poly – A tail added to its 3’ end as the post transcriptional modification. Thus, during reverse transcription this poly – A tail is used as the template strand and a primer of oligo T that is used for the synthesis of the cDNA strand.
3. In RT – PCR the enzyme deoxynucleotydil transferase adds poly – G residues in the __________
a) 5’ end of RNA
b) 3’ end of RNA
c) 3’ end of cDNA
d) 5’ end of cDNA
View Answer
Explanation: During the synthesis of the complementary strand for the cDNA molecule, its 3’ end is unknown. Thus no primer can be formed which can synthesize its complementary strand. Here the enzyme deoxynucleotydil transferase adds poly – G residues in the 3’ end of cDNA so that oligo C primer can be used for the synthesis of its complementary strand.
4. The digestion of mRNA during RT – PCR is carried out by the enzyme ____________
a) Exonuclease
b) RNase H
c) Bal 31
d) Endonuclease
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Explanation: Exonuclease and endonuclease both restrict DNA fragments and Bal 31 is a type of exonuclease. RNase H brings about the mRNA digestion during RT – PCR.
5. How many primers are used in the process of reverse transcriptase amplification?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: The first primer of oligo – T is used during the reverse transcription of the mRNA to cDNA. The cDNA produced is a single stranded molecule thus synthesis of its complementary strand is necessary. A poly G/C tail is added to its 3’ end and thus the second primer is used against this poly G/C tail for the synthesis of the cDNA duplex.
6. From which organism is the enzyme reverse transcriptase isolated?
a) Bacteria
b) Fungi
c) Virus
d) Prions
View Answer
Explanation: Certain viruses have RNA as their genetic material. These viruses carry an extra protein for the synthesis of cDNA so that it can be incorporated efficiently into the host chromosome. This enzyme used by the viruses is a reverse transcriptase. Examples of such viruses are retrovirus, human papiloma virus, etc.
7. The cDNA library provides several advantages over RT – PCR.
a) True
b) False
View Answer
Explanation: The use of 5’ specific primer eliminates the risk of amplification of partial cDNAs. Thus the procedure is so sensitive that the total cellular RNA can be used for RT – PCR, and mRNA separation step is unnecessary. Thus, RT – PCR offers several advantages over cDNA library for the isolation of a specific gene provided enough information is available.
8. ________________ is a modification of RT – PCR.
a) Overlap extension PCR
b) Inverse PCR
c) Thermal cycle sequencing PCR
d) RACE
View Answer
Explanation: A modification of RT – PCR is rapid amplification of cDNA ends or RACE. This process is designed to obtain full length copies of the mRNAs. In RACE, 5’ or 3’ ends of the mRNA are copied into cDNA and are based on one primer specific to an internal site of the mRNA.
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