Explain the process of termination in transcription.

Termination in transcription is the process where RNA synthesis ends when the RNA polymerase reaches a termination signal.

In the process of transcription, the DNA strand is used as a template to synthesise a complementary RNA strand. This process is carried out by an enzyme called RNA polymerase. The termination of transcription is the final stage of this process, where the synthesis of the RNA strand is stopped. This occurs when the RNA polymerase reaches a specific sequence of nucleotides on the DNA template strand known as the termination signal or terminator sequence.

The termination signal is a specific sequence of nucleotides in the DNA that signals the end of the gene. When the RNA polymerase encounters this sequence, it causes the RNA polymerase to detach from the DNA template and release the newly synthesised RNA strand. The exact mechanism of termination can vary depending on the type of cell and the specific gene being transcribed.

In prokaryotic cells, there are two main types of termination: Rho-dependent and Rho-independent. Rho-dependent termination involves a protein factor called Rho that binds to the RNA and moves along it until it reaches the RNA polymerase, causing it to detach from the DNA. Rho-independent termination, on the other hand, involves the formation of a hairpin loop in the RNA that destabilises the interaction between the RNA polymerase and the DNA, causing the polymerase to detach.

In eukaryotic cells, the process is slightly different. The termination signal is followed by a sequence of adenine nucleotides, known as a polyadenylation signal. When the RNA polymerase reaches this signal, it continues to synthesise the RNA for a short distance before proteins associated with the polymerase recognise the signal and cleave the RNA, releasing it from the transcription machinery.

In summary, termination in transcription is a crucial step that signals the end of RNA synthesis. It involves specific sequences in the DNA that signal the RNA polymerase to stop transcription and release the newly synthesised RNA strand. The exact mechanism can vary, but the end result is the same: the completion of a new RNA molecule.