Which enzyme binds to DNA during transcription and separates the DNA strands?

• A. RNA polymerase
• B. DNA helicase
• C. DNA polymerase
• D. Topoisomerase

Answer: (A)

In transcription, the enzyme that binds to DNA and starts RNA synthesis is RNA polymerase. It attaches to promoter regions, melts a short stretch of the DNA to form a transcription bubble, and uses one DNA strand as a template to assemble a complementary RNA strand. This action effectively separates the DNA strands so the template can be read and the RNA can be built. The other enzymes have different primary roles: DNA helicase mainly unwinds DNA during replication, DNA polymerase synthesizes DNA rather than RNA, and topoisomerase relieves torsional stress from unwinding rather than being the main enzyme that separates the strands to begin transcription.