DNA Replication: Introduction

DNA replication is the process of producing two identical replicas from one original DNA molecule. This biological process occurs in all living organisms and is the basis for biological inheritance. DNA is made up of two strands and each strand of the original DNA molecule serves as template for the production of the complementary strand, a process referred to as semiconservative replication. Cellular proofreading and error-checking mechanisms ensure near perfect fidelity for DNA replication.

For the DNA synthesis two key substrate is required.

Substrate: The four deoxynucleoside triphosphates (dNTPs)—deoxyadenosine tri- phosphate (dATP), deoxyguanosine triphosphate (dGTP), deoxycytidine triphos-phate (dCTP), and deoxythymidine triphosphate (dTTP)—are needed as substrates for DNA synthesis.

Primer:template junction: second substrate for the DNA Synthesis is a particular arrangement of ssDNA and dsDNA called primer:template junction.

  • Template. DNA replication cannot occur without a template. A template is required to direct the addition of the appropriate complementary deoxynucleotide to the newly synthesized DNA strand. In semiconservative replication, each strand of parental DNA serves as a template. Then, each template strand and its newly synthesized complementary strand serve as the DNA in daughter cells.
  • Primer. DNA synthesis cannot start without a primer, which prepares the template strand for the addition of nucleotides. The primer must also have an exposed 3’OH because new nucleotides are added to the 3′ end of a primer that is properly base paired to the template strand of DNA, new synthesis is said to occur in a 5′ to 3′ direction.

The DNA synthesis that occurs during the process of replication is catalyzed by enzymes called DNA-dependent DNA polymerases. These enzymes depend on DNA to the extent that they require a DNA template. They are more commonly called DNA polymerases.