Explain the process of elongation in transcription.

Elongation in transcription is the process where RNA polymerase synthesises the RNA transcript by adding nucleotides.

After the initiation phase of transcription, the process of elongation begins. This is the stage where the RNA polymerase enzyme starts to move along the DNA template strand, synthesising the RNA transcript by adding nucleotides to the 3' end of the growing RNA chain. This process continues until a termination signal is reached.

The RNA polymerase enzyme unwinds the DNA double helix just ahead of the transcription bubble, exposing the next section of the template strand to be transcribed. As the RNA polymerase moves along the DNA, it continuously adds nucleotides to the 3' end of the RNA transcript. These nucleotides are complementary to the DNA template strand, ensuring the correct sequence is transcribed.

The RNA polymerase also rewinds the DNA double helix behind it, maintaining the stability and integrity of the DNA molecule. This process of unwinding and rewinding continues as the RNA polymerase moves along the DNA, with the growing RNA transcript being extruded from the enzyme.

The rate of elongation can vary, but it is generally quite rapid, with RNA polymerase able to add hundreds of nucleotides to the RNA transcript every minute. This allows for the efficient production of RNA transcripts, which are essential for the synthesis of proteins and other cellular functions.

Elongation continues until the RNA polymerase encounters a termination signal in the DNA sequence. This signal triggers the end of transcription, with the RNA polymerase detaching from the DNA and releasing the completed RNA transcript. The DNA double helix then fully rewinds, returning to its original state.

In summary, elongation in transcription is a crucial process that allows for the synthesis of RNA transcripts from a DNA template. It involves the RNA polymerase enzyme moving along the DNA, adding nucleotides to the RNA transcript, and rewinding the DNA behind it. This process continues until a termination signal is reached, at which point the RNA transcript is complete and is released from the enzyme.