1
Question
If the “annealing” step is missed during PCR, what would be its effect on the entire process?
I. DNA strands will not separate
II. Primers will not attach
III. DNA Polymerase would not work
IV. DNA will not extend
If the “annealing” step is missed during PCR, what would be its effect on the entire process?
I. DNA strands will not separate
II. Primers will not attach
III. DNA Polymerase would not work
IV. DNA will not extend
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Solution
The correct option is B II, III & IV
PCR or polymerase chain reaction is a technique used in molecular biology to create several copies of a certain DNA segment.
PCR occurs in three steps:
1. Denaturation: It involves breaking the hydrogen bonds between the two strands of double stranded DNA by exposing them to a high temperature (94-96°C). This helps in separating the two strands of a double stranded DNA.
2. Annealing: The primers bind to their complementary sequences on the template DNA and serve as the starting point for the synthesis of DNA. This reaction occurs around 55-65°C.
3. Extension: The bases are added to the 3' end of the primer by the Taq polymerase enzyme. This elongates the DNA in the 5' to 3' direction. It is carried out at 72°C. Finally, the complementary strands are formed.
Hence if the "annealing" step is missed, the primers will not attach to the DNA strands. DNA polymerase cannot function without a primer. This is because DNA polymerase cannot initiate polynucleotide chain synthesis. Taq polymerase enzyme adds the new deoxyribonucleotide bases to the 3' end of the primer. If primer is not present, then Taq polymerase will have no place to add nucleotides and carry out amplification. Therefore, DNA elongation will not take place.
PCR or polymerase chain reaction is a technique used in molecular biology to create several copies of a certain DNA segment.
PCR occurs in three steps:
1. Denaturation: It involves breaking the hydrogen bonds between the two strands of double stranded DNA by exposing them to a high temperature (94-96°C). This helps in separating the two strands of a double stranded DNA.
2. Annealing: The primers bind to their complementary sequences on the template DNA and serve as the starting point for the synthesis of DNA. This reaction occurs around 55-65°C.
3. Extension: The bases are added to the 3' end of the primer by the Taq polymerase enzyme. This elongates the DNA in the 5' to 3' direction. It is carried out at 72°C. Finally, the complementary strands are formed.
Hence if the "annealing" step is missed, the primers will not attach to the DNA strands. DNA polymerase cannot function without a primer. This is because DNA polymerase cannot initiate polynucleotide chain synthesis. Taq polymerase enzyme adds the new deoxyribonucleotide bases to the 3' end of the primer. If primer is not present, then Taq polymerase will have no place to add nucleotides and carry out amplification. Therefore, DNA elongation will not take place.
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