Final answer:
The hydrogen bonds between complementary bases are broken when mRNA separates from DNA, due to their relatively low strength which allows the DNA strands to easily 'unzip' during transcription.
Step-by-step explanation:
The type of bond that is broken when mRNA separates from DNA during transcription is the hydrogen bond between the complementary nitrogenous bases. These hydrogen bonds are weaker than the covalent bonds that hold the atoms within each sugar-phosphate backbone, making separation energetically feasible during normal cellular processes. The characteristic of the hydrogen bond that allows for this separation is its relatively low bond strength, which permits the DNA strands to 'unzip' and the mRNA to be synthesized based on the DNA template.
Temperature or chemicals can be used to induce this separation in the laboratory, a process known as DNA denaturation. This property is critical in biotechnology, allowing scientists to manipulate and analyze DNA and RNA. Finally, the helicase enzyme naturally facilitates the unzipping of DNA during replication by breaking these same hydrogen bonds.