This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Fundamentals of PCR”.
1. PCR is a DNA amplifying in vivo method ______
Explanation: A powerful method for amplifying particular DNA segment is the polymerase chain reaction. This procedure is carried out entirely biochemically, that is invitro.
2. Which of the following is a mismatch?
a) Polymerase – Taq polymerase
b) Template – double stranded DNA
c) Primer – oligonucleotide
d) Synthesis – 5’ to 3’ direction
Explanation: PCR uses the enzyme DNA polymerase that directs the synthesis of DNA from deoxynucleotide substrates on one stranded DNA template. DNA polymerase synthesizes DNA in a 5’→3’ direction and can add nucleotides in the 3’ end of a custom – designed oligonucleotide.
3. Annealing of primer is facilitated by complementary region ___________
Explanation: A synthetic oligonucleotide is annealed to a single stranded DNA template that contains a complementary region. DNA polymerase thus uses this annealed primer to elongate the new strand.
4. Primer used for the process of polymerase chain reaction are ______________
a) Single stranded DNA oligonucleotide
b) Double stranded DNA oligonucleotide
c) Single stranded RNA oligonucleotide
d) Double stranded RNA oligonucleotide
Explanation: Two single stranded, oligonucleotide is synthesized and used as a primer. The primers thus produces binds to the denatured DNA and polymerase starts its synthesis in the 5’ to 3’ direction.
5. Polymerase used for PCR is extracted from _____________
a) Escherichia coli
b) Homo sapiens
c) Thermus aquaticus
d) Saccharomyces cerevisiae
Explanation: Amplification is usually carried out by the DNA polymerase I enzyme from Thermus aquaticus. As this organism lives in hot springs, Taq polymerases are thermostable thus they are resistant to high temperature.
6. How many DNA duplex is obtained from one DNA duplex after 4 cycles of PCR?
Explanation: After each cycle the number of duplexes doubles itself thus after the first cycle there are 2 DNA duplexes. A duplex has 2 DNA strands thus after second cycle there will be 4 Duplexes, after third cycle there will be 8 DNA duplex. Lastly, after the 4th cycle there will be 16 duplexes.
7. At what temperature do denaturation of DNA double helix takes place?
Explanation: The polymerase chain reaction is started by heating the mixture at 94˚C. At this temperature the hydrogen bonding between the nucleotide bases melts thus separating the two DNA strands.
8. At what temperature do annealing of DNA and primer takes place?
Explanation: After the denaturation of the two strands the temperature is decreased to 50 – 60˚C. At this temperature the primers anneal to their complementary segments. Thus as 54˚ lies within this range option b is the correct option.
9. The temperature at which DNA synthesis takes place is 74˚C _______________
Explanation: The DNA synthesis in polymerase chain reaction takes place at 74˚C. This is usually set at 74˚C because this is just below the optimum temperature of functioning of the Taq polymerase.
Sanfoundry Global Education & Learning Series – Molecular Biology.
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