How are the hydrogen bonds broken during DNA replication? Is it done by the DNA polymerases?
During DNA replication, the hydrogen bonds between the complementary base pairs (adenine-thymine and cytosine-guanine) in the DNA molecule are indeed broken. This breaking of hydrogen bonds is a crucial step in the process of DNA replication. However, it is not directly done by DNA polymerases.
The DNA polymerases, such as DNA polymerase III in prokaryotes or DNA polymerase α, β, δ, and ε in eukaryotes, are the enzymes responsible for catalyzing the formation of new DNA strands by adding nucleotides to the growing DNA chain.
The hydrogen bond breaking in DNA replication is achieved by another group of enzymes called DNA helicases. These enzymes are responsible for unwinding and separating the two DNA strands at the replicating fork, creating a replication bubble.
DNA helicases use the energy from ATP hydrolysis to move along the DNA molecule, disrupting the hydrogen bonds between the base pairs and unwinding the double helix structure. This unwinding provides single-stranded DNA templates that can be used as templates for DNA synthesis.
After the hydrogen bonds are broken and the DNA helix is unwound, DNA polymerases come into play. They bind to the single-stranded DNA template and start synthesizing new complementary DNA strands by adding nucleotides according to the complementary base pairing rules. The newly synthesized DNA strands will eventually re-establish hydrogen bonds with the corresponding nucleotides on the template strands, forming a new, complete DNA double helix.
In summary, while DNA polymerases are responsible for synthesizing new DNA strands during replication, the breaking of hydrogen bonds between the base pairs is facilitated by DNA helicases.