DNA transcription is the process of creating an RNA copy of a DNA sequence. Here's a breakdown of how it works:
The Key Player: RNA Polymerase
- The main enzyme responsible for DNA transcription is RNA polymerase.
- This enzyme moves along the DNA strand, unwinding the double helix at its active site. This allows access to the nucleotide bases.
- According to the reference, RNA polymerase (pale blue) moves stepwise along the DNA, unwinding the DNA helix at its active site.
The Process Step-by-Step
- Unwinding: RNA polymerase attaches to the DNA at a specific region called the promoter. It then begins to unwind the double helix.
- Base Pairing: As the DNA unwinds, RNA polymerase uses one strand of the DNA as a template. It adds free RNA nucleotides, pairing them with the complementary DNA bases:
- Adenine (A) in DNA pairs with Uracil (U) in RNA.
- Guanine (G) in DNA pairs with Cytosine (C) in RNA.
- Cytosine (C) in DNA pairs with Guanine (G) in RNA.
- Thymine (T) in DNA pairs with Adenine (A) in RNA.
- Elongation: The RNA polymerase continues to move along the DNA, adding nucleotides one by one, extending the RNA molecule.
- The reference notes the polymerase adds nucleotides (small "T" shapes) one by one.
- Termination: Transcription ends when the RNA polymerase reaches a specific termination signal in the DNA sequence. The newly formed RNA molecule is released, and the RNA polymerase detaches from the DNA.
- Processing (in Eukaryotes): The newly transcribed RNA, called pre-mRNA, undergoes modifications like splicing, capping, and polyadenylation to become mature mRNA ready for translation. This doesn't apply to all RNA types.
A Summary Table
| Step | Description | Enzyme Involved |
|---|---|---|
| Initiation | RNA polymerase binds to the DNA at the promoter and unwinds the double helix. | RNA polymerase |
| Elongation | RNA polymerase adds RNA nucleotides to the growing RNA strand, using the DNA as a template. | RNA polymerase |
| Termination | RNA polymerase reaches the termination signal, releases the RNA, and detaches from DNA. | RNA polymerase |
| Processing (Eukaryotes) | pre-mRNA undergoes modifications. | Various enzymes |
Key Takeaways
- Transcription is the creation of an RNA copy from a DNA template.
- RNA polymerase is the central enzyme that carries out this process.
- The process involves unwinding the DNA, pairing RNA nucleotides to the DNA template, and then releasing the newly synthesized RNA.
- In eukaryotes, the RNA often needs further modifications before being ready for translation.
