Select all that apply
Choose all statements that accurately describe the transcription bubble.
Multiple select question.
It contains an RNA-DNA hybrid, about 8-10 bp long
It moves along the DNA at a rate of about 50nt/sec
It is stationary, with the DNA strand slowly threaded through it at a rate of about 50nt/sec
The growing RNA is compacted within a specialized compartment inside the bubble
The growing RNA strand protrudes from the bubble
The newly made RNA within the bubble makes a single nucleotide contact with DNA at the 3′ end
The Correct Answer and Explanation
The correct answers are:
- ✅ It contains an RNA-DNA hybrid, about 8–10 bp long
- ✅ It moves along the DNA at a rate of about 50 nt/sec
- ✅ The growing RNA strand protrudes from the bubble
Explanation:
The transcription bubble is a temporary unwound region of DNA formed during transcription, where RNA polymerase synthesizes a complementary RNA strand from the DNA template. It is an essential structure that ensures accurate and efficient transcription by allowing access to the template strand.
✅ 1. It contains an RNA-DNA hybrid, about 8–10 bp long
This is true. Within the transcription bubble, the newly synthesized RNA strand forms a short RNA-DNA hybrid with the template strand, typically 8–10 base pairs in length. This hybrid is stabilized within the active site of RNA polymerase and plays a crucial role in transcription fidelity.
✅ 2. It moves along the DNA at a rate of about 50 nt/sec
This is also true. In prokaryotes like E. coli, the RNA polymerase progresses along the DNA template at approximately 50 nucleotides per second under normal conditions. In eukaryotes, the rate may vary but is generally in a similar range during the elongation phase.
❌ 3. It is stationary, with the DNA strand slowly threaded through it at a rate of about 50 nt/sec
This is false. The transcription bubble moves with the RNA polymerase as it travels along the DNA template. The idea of the polymerase being stationary while the DNA is threaded through it is not accurate in the context of cellular transcription.
❌ 4. The growing RNA is compacted within a specialized compartment inside the bubble
This is false. The growing RNA is not compacted within the bubble; instead, it extends out of the RNA polymerase complex. There is no special compartment for RNA compaction within the bubble.
✅ 5. The growing RNA strand protrudes from the bubble
This is true. As RNA synthesis proceeds, the RNA strand exits through a channel in the RNA polymerase enzyme, protruding from the transcription complex. Only the 3’ end remains within the bubble as it is being actively extended.
❌ 6. The newly made RNA within the bubble makes a single nucleotide contact with DNA at the 3′ end
This is false. The RNA-DNA hybrid within the bubble is longer than a single nucleotide—it typically spans about 8–10 base pairs. Therefore, it is not limited to a single nucleotide contact.