Here's a detailed explanation:
Initiation:
1. RNA polymerase first recognizes and binds to specific DNA sequences called promoters. These promoters signal the start of a gene and provide the necessary cues for transcription to begin.
2. The enzyme assembles at the promoter region, along with other transcription factors, to form a transcription initiation complex.
3. Once bound to the promoter, RNA polymerase undergoes a conformational change, facilitating the unwinding of the DNA double helix. This creates a transcription bubble, exposing two DNA strands.
Elongation:
4. RNA polymerase starts transcribing the DNA sequence from the 5' (five prime) end to the 3' (three prime) end. It synthesizes a complementary RNA molecule based on the DNA template strand.
5. As RNA polymerase moves along the DNA, it reads the sequence of nucleotides in the template strand and sequentially adds complementary RNA nucleotides (A, U, C, and G) to the growing RNA molecule.
6. The base-pairing rules apply, ensuring that adenine (A) pairs with uracil (U), cytosine (C) with guanine (G), and so on. This process results in the elongation of the RNA molecule, forming an RNA transcript that faithfully copies the DNA sequence, excluding the thymine (T), which is replaced with uracil (U) in RNA.
Termination:
7. RNA polymerase continues to transcribe the DNA until it reaches a termination signal, which is usually a specific DNA sequence. These signals cause the enzyme to dissociate from the template strand, leading to the release of the newly formed RNA transcript.
8. Once RNA polymerase detaches, the two DNA strands reanneal to their original double-helical structure.
The RNA product generated during transcription may undergo further modifications, such as splicing, capping, and polyadenylation, before it becomes a mature messenger RNA (mRNA) that can direct protein synthesis.
