DNA replication is the process in which DNA is duplicated. This important process happens before the cell divides. In eukaryotes, replication takes place in the nucleus, whereas in prokaryotes, it takes place in the cytoplasm of the cell.
Initiation
– Initiation always occurs at the same spot on a DNA molecule and these are called origins of replication.
– Enzymes called helicase and topoisomerase work together to ‘unzip’ the double stranded DNA molecule.
– Other proteins are also present to hold the strands apart, keeping them separated.
– A replication fork is created.
Elongation
– RNA primase puts down and RNA primer, which helps to initiate replication
– DNA polymerase comes and adds complementary bases along the DNA strand. Adenine is paired with thymine, and cytosine is paired with guanine.
– DNA can only be made in the 5’-3’ direction and as a result, one strand (leading) is made continuously and one strand (lagging) is not.
Leading Strand
– DNA polymerase reads the original 3’-5’ DNA strand, synthesizing a 5’-3’ copy.
– This strand is made continuously.
Lagging Strand
– DNA polymerase does not work in the 5’-3’ direction on the original DNA strand and thus, the lagging strand is made discontinuously.
– RNA primase synthesizes an RNA primer and DNA polymerase synthesizes the strand in short segments called ‘Okazaki Fragments’.
– Gaps between fragments are then joined together by DNA ligase to form one complete strand.
Termination
– When DNA polymerase reaches the end of the strands.
– RNA primers are removed and the ends are not replicated as a result.
DNA is replicated in a semiconservative manner. That means each new DNA molecules consists of 1 strand of the original DNA and 1 strand of the newly synthesized DNA. With DNA replication, many different mechanism repair steps, which involve numerous proteins, occur to fix any possible errors that may have occurred during the replication process.
This article was written for you by Samantha, one of the tutors with Test Prep Academy.