INITIATION, ELONGATION AND TERMINATION
Initiation, elongation, and termination are the three stages in the process of transcription, which is the synthesis of RNA from a DNA template.
1) Initiation: This is the beginning of transcription. In this stage, an enzyme called RNA polymerase binds to the DNA at a specific sequence of nucleotides called the "promoter" region. The RNA polymerase opens up the DNA double helix at this point, exposing the nucleotides, and then begins to move along the DNA.
2) Elongation: This is the stage during which RNA polymerase moves along the DNA, synthesizing an RNA molecule that is complementary to one strand of the DNA template. As RNA polymerase moves along, it reads the DNA template and uses the nucleotides to build the RNA molecule.
3) Termination: This is the end of transcription. In this stage, RNA polymerase reaches a terminator sequence in the DNA, which signals the end of the gene being transcribed. At this point, RNA polymerase disengages from the DNA template, and the newly synthesized RNA molecule is released. The RNA molecule can then be used as a template for translation, the process by which proteins are synthesized.
Initiation, elongation, and termination are the three steps involved in the process of transcription, which is the synthesis of RNA from a DNA template. Let's go through each step one by one:
1. Initiation:
- The first step in transcription is initiation, where RNA polymerase enzyme recognizes and binds to a specific region on the DNA called the promoter.
- The promoter region contains a specific sequence of nucleotides that signals the start of transcription.
- Once the RNA polymerase binds to the promoter region, it begins to unwind and separate the DNA strands.
2. Elongation:
- After initiation, the elongation phase of transcription begins.
- In this phase, the RNA polymerase travels along the DNA template strand and adds complementary RNA nucleotides.
- As the RNA polymerase moves along the DNA template, it continuously synthesizes an RNA molecule by linking the RNA nucleotides together in a complementary sequence to the DNA template.
- The RNA chain grows in length as the RNA polymerase moves along the DNA template strand.
- Meanwhile, the DNA strands re-anneal behind the RNA polymerase.
3. Termination:
- The final step in transcription is termination.
- Termination involves the recognition of a specific termination signal on the DNA template sequence.
- Once the termination signal is encountered, the RNA polymerase and the newly synthesized RNA molecule are released from the DNA template.
- The released RNA molecule, called the primary transcript or pre-mRNA, is then ready for further processing and modification in eukaryotes before it can be used for protein synthesis.
In summary, initiation marks the start of transcription, elongation involves the synthesis of an RNA molecule using DNA as a template, and termination signals the end of transcription. These steps collectively allow the cell to transcribe DNA into RNA, providing a template for protein synthesis.