DNA REPLICATION

The Roles of Enzymes in DNA ReplicationBy definition, DNA Replication is the process of making a copy of itself. In other words existing strands of DNA serve as templates (pattern) for building a new strand of DNA. DNA replication occurs during the (S) synthesis phase of the cell cycle, before a cell divides. This process includes three steps.

DNA ReplicationSTEP 1: Enzymes called DNA helicases unwind the DNA

molecules by breaking the hydrogen bonds between bases. The point at which the DNA molecule is separated is called the replication fork.

STEP 2: At the replication fork, enzymes called DNA polymerases move along each strand to add complimentary nucleotides to the exposed bases [according to ‘Base Pairing Rules’. . . A (adenine) pairs with T (thymine); and C (cytosine) pairs with G (guanine).

STEP 3: Once DNA replication is completed (DNA making a copy of itself), DNA polymerase is signaled to detach. This process produces two DNA molecules that are identical to the original molecule.

DNA ReplicationChecking for Errors:In the course of DNA Replication, errors sometimes occur and

the wrong nucleotide is added to the new strand. DNA polymerases help reduce the number of errors by “proofreading” the newly made DNA strands. If there is a mismatched nucleotide, polymerases will backtrack and remove the incorrect base, replacing it with the correct one.

The Rate of Replication: In prokaryotes, which have circular DNA, two replication

forks begin at a single point, meet in the middle. In eukaryotes, which have strands of DNA, there are

multiple replication forks which help speed up the process of replication.