Question

Explain the roles of DNA helicase, DNA polymerase, and DNA ligase in the process of DNA replication.

Short answer

DNA helicase unwinds the double-stranded DNA by breaking hydrogen bonds between base pairs, creating two single-stranded templates. DNA polymerase synthesizes new DNA strands complementary to the templates, using continuous leading strand synthesis and discontinuous lagging strand synthesis through Okazaki fragments. DNA ligase joins Okazaki fragments on the lagging strand, forming a continuous DNA molecule.

Step-by-step solution

1. DNA Helicase

DNA helicase is an enzyme that plays a crucial role in the process of DNA replication. Its primary function is to separate the two complementary strands of the DNA double helix by breaking the hydrogen bonds between the base pairs. This is important as it creates two single-stranded DNA templates, which serve as templates for the synthesis of new DNA strands.

2. DNA Polymerase

DNA polymerase is another essential enzyme involved in DNA replication. It is responsible for synthesizing new DNA strands complementary to the template strands. The DNA polymerase adds deoxyribonucleotides (nucleotides containing the sugar deoxyribose, a phosphate group, and one of the four nitrogenous bases) to the 3' end of the growing DNA strand, using the original template strand as a guide. DNA polymerases can only synthesize DNA in the 5' to 3' direction. This continuous synthesis is called the leading strand synthesis. For the lagging strand, DNA replication is discontinuous and occurs through the formation of Okazaki fragments. DNA polymerase synthesizes these fragments, which will later be joined together by DNA ligase.

3. DNA Ligase

DNA ligase is the enzyme responsible for joining together the Okazaki fragments formed during the replication of the lagging strand. It seals the nicks between the fragments by catalyzing the formation of a phosphodiester bond between the adjacent 3' hydroxyl and 5' phosphate ends of the DNA fragments. This creates a continuous DNA strand and ensures that the newly synthesized DNA is a complete and accurate copy of the original template strand. In summary, DNA helicase, DNA polymerase, and DNA ligase are essential enzymes involved in the process of DNA replication. They each play specific roles, with DNA helicase separating the double-stranded DNA, DNA polymerase synthesizing new DNA strands using the template strands, and DNA ligase linking the Okazaki fragments to form a continuous DNA molecule.