Transcription machinery—naming the active complex In molecular genetics, what is the term for the active complex consisting of RNA polymerase bound to a DNA template while synthesizing the nascent RNA strand (with a locally unwound region of DNA)?

Introduction / Context:
The question tests core vocabulary in gene expression. During transcription, RNA polymerase, the DNA template, and the newly forming RNA strand exist together in a dynamic complex. The local unwinding of DNA creates a short region where base pairing is temporarily disrupted to allow templated RNA synthesis.

Given Data / Assumptions:

• An enzyme (RNA polymerase) is engaged on a DNA template.
• A nascent RNA transcript is being elongated.
• There is a short window of locally melted DNA within which templating occurs.

Concept / Approach:
When RNA polymerase initiates and elongates RNA, it forms a moving “open complex.” The locally unwound DNA (typically about 12–17 base pairs) plus polymerase and nascent RNA is widely known as the transcription bubble. This contrasts with DNA replication, where two forks and a much larger region of unwound DNA form a replication bubble.

Step-by-Step Solution:
Recognize that the process described is RNA synthesis from DNA.Identify the structural state: a locally unwound DNA segment within the polymerase.Recall the standard term: transcription bubble (also called open complex).Select the corresponding option.

Verification / Alternative check:
Biochemical and structural studies (footprinting, cryo-EM) show polymerase encloses a melted DNA region where the RNA–DNA hybrid is formed, matching the definition of a transcription bubble.

Why Other Options Are Wrong:

• Replication bubble: Refers to DNA replication with bidirectional forks, not transcription.
• Translation bubble: No such term; translation occurs on ribosomes.
• None of these / Transcription fork: The accepted term is transcription bubble or open complex; “transcription fork” is not standard.

Common Pitfalls:
Confusing terms between replication and transcription or assuming large-scale DNA unwinding is required for transcription.

Final Answer:
Transcription bubble.