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Question
Statement 1: PCR can be performed on a random unsequenced stretch of DNA.
Statement 2: Proofreading activity by Taq polymerase is done in 3’-5’ direction.
Statement 1: PCR can be performed on a random unsequenced stretch of DNA.
Statement 2: Proofreading activity by Taq polymerase is done in 3’-5’ direction.
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Solution
The correct option is D Both the statements are false
Polymerase Chain Reaction(PCR) is a technique to make many copies of a specific DNA stretch in vitro. This molecular technique can rapidly make a million to billions of copies of a specific DNA. A a tiny quantity of DNA can be amplified into a large amount, to study in detail.
PCR requires a few things - a DNA template which is to be amplified, a small chemically synthesised oligonucleotide sequence complementary to the 3’ end of the template DNA for initiation of replication called primers, DNA polymerase enzyme like Taq polymerase.
Although this technique of amplifying DNA is one of the groundbreaking inventions of the biotechniques which made this a ubiquitous tool in all the laboratories around the world, it has one major drawback, that it cannot be performed on a random sequence of DNA. The DNA sequence to be amplified needs to be known and accordingly, the primer is designed.
There are many thermostable polymerases that are used in the process of PCR, among which all Taq polymerases; isolated from a thermophilic bacterium called Thermus aquaticus, are mostly used. It synthesises the DNA in 5’ to 3’ direction according to the nucleotide bases on the template DNA. This polymerase has an error rate of 2*10-4 error/base. This is due to the fact that this polymerase enzyme does not have a proofreading activity like other thermostable polymerases like Pfu, Vent etc. The proofreading activity of these polymerases increases the fidelity of the PCR products by many folds, which is absent in the case of Taq polymerase.
Polymerase Chain Reaction(PCR) is a technique to make many copies of a specific DNA stretch in vitro. This molecular technique can rapidly make a million to billions of copies of a specific DNA. A a tiny quantity of DNA can be amplified into a large amount, to study in detail.
PCR requires a few things - a DNA template which is to be amplified, a small chemically synthesised oligonucleotide sequence complementary to the 3’ end of the template DNA for initiation of replication called primers, DNA polymerase enzyme like Taq polymerase.
Although this technique of amplifying DNA is one of the groundbreaking inventions of the biotechniques which made this a ubiquitous tool in all the laboratories around the world, it has one major drawback, that it cannot be performed on a random sequence of DNA. The DNA sequence to be amplified needs to be known and accordingly, the primer is designed.
There are many thermostable polymerases that are used in the process of PCR, among which all Taq polymerases; isolated from a thermophilic bacterium called Thermus aquaticus, are mostly used. It synthesises the DNA in 5’ to 3’ direction according to the nucleotide bases on the template DNA. This polymerase has an error rate of 2*10-4 error/base. This is due to the fact that this polymerase enzyme does not have a proofreading activity like other thermostable polymerases like Pfu, Vent etc. The proofreading activity of these polymerases increases the fidelity of the PCR products by many folds, which is absent in the case of Taq polymerase.
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