During transcription elongation, what happens?

• A. RNA polymerase detaches from DNA and rebinds anew.
• B. First NTPs are added to initiate RNA synthesis.
• C. RNA polymerase reads the template 5'→3' and synthesizes RNA 3'→5'.
• D. RNA polymerase adds nucleotides to the growing RNA, reads the template 3'→5', and synthesizes RNA 5'→3'.

Answer: (D)

During transcription elongation, the enzyme remains bound to the DNA and extends the RNA chain by adding nucleotides one by one. It reads the template strand in the 3' to 5' direction and builds the new RNA in the 5' to 3' direction, adding nucleotides that are complementary to the template. This combination—adding nucleotides to the growing RNA, reading the template 3'→5', and synthesizing RNA 5'→3'—precisely describes elongation.

The other scenarios correspond to other phases or incorrect directions: detaching and rebinding reflects initiation/ promoter clearance or termination steps rather than elongation; initiating with the first NTPs is initiation; and reading the template in the 5'→3' direction with RNA synthesis in the 3'→5' direction reverses the correct order of operations for transcription.