DNA Replication is a very simple process if you know how it works. It is a process by which two identical dsDNA strands are produced by one dsDNA( double-stranded DNA)

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Just as there are many ingredients to a dish, DNA replication also requires some raw materials. The primary requirements are

  • A DNA Template

  • dNTPs( deoxy-ribonucleotide phosphate): These are the energy sources for the process

  • Enzymes/ Proteins

There are 7 major proteins required

  1. Initiator Proteins: These are the proteins that recognize a specific site within the Origin of Replication from where the replication of DNA starts.

  2. Helicase: They help in the unwinding/opening of DNA by breaking Hydrogen bonds between two base pairs.

  3. Single-Strand Binding Proteins or SSB Proteins: They prevent the rejoining of two polynucleotide chains of DNA.

  4. Primase: It is a type of RNA polymerase that helps in synthesizing RNA primers, which act as a starting point for DNA synthesis.

  5. Topoisomerase: It prevents the supercoiling between two polynucleotide chains.

  6. Ligase: It helps in the joining of DNA fragments.

  7. DNA Polymerase: It is the main enzyme required for the replication of DNA. It has the following four types

  • DNA Polymerase I: It removes the RNA primers and adds new nucleotides in their place.

  • DNA Polymerase II: It catalyzes the repair of nucleotide base pairs.

  • DNA Polymerase III: It is the primary enzyme required for the DNA replication process.

  • DNA Polymerase IV: It is the enzyme that helps a cell tolerate DNA damage.

  • DNA Polymerase V: It is the enzyme responsible for repairing DNA in bacterias.

DNA Replication starts by unwinding dsDNA with the help of the helicase enzyme to form a replication fork. The DNA has two strands. One strand runs in the direction 3'to 5' and is known as the leading strand. The other strand runs in the direction 5' to 3' and is known as the lagging strand of DNA.

After this, the RNA Primer attaches itself to the 3' end of the leading strand and then the synthesis of the new strand begins. This type of synthesis is known as Continuous.

DNA synthesis only takes place in the 5' to 3' direction.

In the lagging strand, RNA Primers attach at many different positions, and the synthesis of DNA takes place in small fragments. This type of synthesis is known as Discontinuous. The small fragments are later joined together by lipase enzyme to form a continuous strand.

Semi Conservative mode of DNA Replication

It was proposed by Watson and Crick and was proved by Matthew Meselson and Franklin Stahl in the Meselson-Stahl experiment.

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To learn more about DNA, make sure you check out my previous blog.

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