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  • The enzyme DNA polymerase in E. coli is a DNA dependent polymerase and also has the ability to proofread the DNA strand being synthesised. Explain. Discuss the dual polymerase.

The enzyme DNA polymerase in E. coli is a DNA dependent polymerase and also has the ability to proofread the DNA strand being synthesised. Explain. Discuss the dual polymerase.

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Enzyme activities of DNA-dependent DNA polymerase (dual polymerase) are discussed below:

  • Polymerase Activity:
    The DNA-dependent DNA polymerase synthesizes the new DNA strand by adding nucleotides complementary to the template strand in the 5′ to 3′ direction. This activity is essential for DNA replication, ensuring the elongation of the new strand based on the template.

  • Proofreading and Exonuclease Activity:
    The enzyme has 3′ to 5′ exonuclease activity, which enables it to proofread the newly synthesized DNA. If a mismatched nucleotide is incorporated, the enzyme detects it, removes the incorrect nucleotide, and replaces it with the correct one, improving the accuracy of DNA replication.

  • DNA Repair Function:
    DNA polymerase also plays a role in repairing DNA damage caused by environmental factors such as UV radiation. It is involved in the nucleotide excision repair (NER) pathway, where it helps remove damaged nucleotides and fills in the correct ones, ensuring the DNA remains intact.

  • High Fidelity in Replication:
    The enzyme's proofreading ability, combined with its polymerase function, ensures high fidelity during DNA replication. It reduces the error rate of replication to about 1 in 10^7 nucleotides, preventing mutations from accumulating in the genome.

  • Template-Dependent Elongation:
    The DNA-dependent DNA polymerase uses the parent DNA as a template for synthesizing the new strand. The enzyme adds nucleotides to the growing strand by recognizing the complementary bases of the template strand, ensuring that the genetic information is accurately passed on to the new DNA molecule.

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