Question

How does DNA polymerase work?

Answer 1

DNA polymerase belongs to the class of enzymes- Polymerases. They are responsible for the formation of long chains of polymers or nucleic acids.

Complete answer:
DNA is a molecule that contains two polynucleotide chains that run anti-parallel to each other and contains the genetic code of an organism. A polynucleotide is a polymer of many nucleotides. These nucleotides are the building block of nucleic acids and consist of a sugar molecule, phosphate group, and nitrogenous bases. In a DNA molecule, deoxyribose is the sugar, and Adenine, Thymine, Guanine, and Cytosine are the nitrogenous bases. These polynucleotides are linked together by the covalent bonds to form a long double-helical structure of DNA.

The DNA polymerases are the enzymes that are used in the process of DNA replication and help in the synthesis of DNA from its precursor molecules. These enzymes do not form a new DNA strand from the scratch. They synthesize a new DNA strand by replicating from the already existing template strands of the DNA molecule.
In the process of DNA replication, the helicase enzymes unwind the double-helical structure of DNA. This results in the exposure of the two strands of DNA, which are further used as templates for replication. DNA primase synthesizes the RNA primer, which is responsible for the initiation of the replication process. The RNA primer is added with the first nucleotide by the DNA polymerase.

The DNA polymerase starts sliding on the single-stranded template chain of the DNA molecule. They read the nucleotide bases on the template strand and add complementary nucleotide bases to the RNA primer. They add nucleotides only to 3’-OH or three prime ends of the newly formed nucleotide chain. Therefore, they read the nucleotide chain in 3’-5’ direction. The newly formed chain runs from the 5’-3’ direction. The process of elongation of the DNA chain is terminated- when there is no more template strand left to be decoded or when the enzyme meets the replication fork. The RNA primase is removed, and the nucleotides are joined together by the enzyme- DNA ligase. So by the end of replication, we have two strands of DNA molecules that are complementary to each other and identical to their parent molecule.

DNA polymerase can correct or rectify its mistakes in the process of replication- and also produce the sugar-phosphate bonds between the nucleotides. They are needed every time a cell needs to duplicate its DNA material to pass it to their daughter cells or progeny.

Note: The DNA polymerase reads nucleotides only in the 3’-5’ direction. Thus, it can read the 3’-5’ strand continuously and form a leading or continuous strand of DNA. On the 5’-3’ strand, the nucleotides are read from the 3’-5’ direction in fragments called Okazaki fragments. This strand is called the lagging or the discontinuous strand.