The Role of Enzymes DNA replication is carried out by a series of enzymes. They first “unzip” a molecule of DNA by breaking the hydrogen bonds between base pairs and unwinding the two strands of the molecule. Each strand then serves as a template for the attachment of complementary bases.

DNA Polymerase The principal enzyme involved in DNA replication is called DNA polymerase. DNA polymerase is an enzyme that joins individual nucleotides to produce a new strand of DNA. DNA polymerase also “proofreads” each new DNA strand, ensuring that each molecule is a perfect copy of the original.

The Role of Enzymes DNA polymerase is an enzyme that joins individual nucleotides to produce a new strand of DNA.

Ligase Okazaki fragments need to be “welded” together DNA ligase bonds the Okazaki fragments, that make up the lagging strand, together

DNA Helicase DNA helicase separates double-stranded DNA into single strands allowing each strand to be copied DNA helicases unwind DNA at positions called origins where synthesis will be initiated DNA helicase continues to unwind the DNA forming a structure called the replication fork

DNA Helicase The process of breaking the hydrogen bonds between the nucleotide base pairs in double-stranded DNA requires energy helicases use the energy stored in ATP

RNA Primase Primase is an enzyme that synthesizes short RNA sequences called primers primers serve as a starting point for DNA synthesis on the lagging strand

RNA Primase Primase functions by synthesizing short RNA sequences that are complementary to a single-stranded piece of DNA, which serves as its template primers are necessary because DNA polymerases can only attach new DNA nucleotides to an existing strand of nucleotides primase serves to prime and lay a foundation for DNA synthesis

Telomeres The tips of chromosomes are known as telomeres. The ends of DNA molecules, located at the telomeres, are particularly difficult to copy. Over time, DNA may actually be lost from telomeres each time a chromosome is replicated. An enzyme called telomerase compensates for this problem by adding short, repeated DNA sequences to telomeres, lengthening the chromosomes slightly and making it less likely that important gene sequences will be lost from the telomeres during replication.