4 public questions tagged with this topic.
Ligase is not required for PCR. Instead, Taq polymerase, primers, and a DNA template are essential.
Ref: NCERT Class 12 Biology Chapter 9: Biotechnology: Principles and Processes Polymerase Chain Reaction - PCR and Applications
Taq polymerase is a thermostable enzyme used to amplify DNA sequences during PCR.
Ref: NCERT Class 12 Biology Chapter 9: Biotechnology: Principles and Processes Polymerase Chain Reaction - PCR and Applications
PCR buffer typically contains Tris-HCl, potassium chloride, and magnesium chloride adjusted to pH 8.3-8.8 at 25°C, which shifts to approximately 7.2 at extension temperature due to temperature coefficient of Tris. This system stabilizes pH against proton changes from dNTP hydrolysis, maintains ionic strength required for enzyme activity, and supports polymerase conformation. It does not hydrolyze DNA, dissolve template, or cool reaction, as thermal cycling is mediated by instrument block. Stable pH environment maximizes enzyme processivity, fidelity, and reproducibility across cycles.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
Divalent magnesium ions serve as an essential cofactor for DNA polymerases in PCR. Mg2+ coordinates with phosphate oxygens of dNTPs at the active site, facilitates nucleophilic attack by 3' hydroxyl, stabilizes negative charges during phosphodiester bond formation, and influences primer-template duplex stability. Concentration critically affects enzyme activity, fidelity, specificity, and primer annealing. Unlike an enzyme that catalyzes reaction itself, buffer that maintains pH, or template that encodes sequence, Mg2+ is a non-protein chemical activator indispensable for catalytic function and typically used at 1.5-2.5 mM.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
