During elongation, which is one of the three steps of transcription, RNA polymerase, an enzyme, synthesizes RNA, a nucleic acid, by adding nucleotides, the building blocks of RNA, to the RNA strand. The template strand of DNA, the genetic material, serves as a guide for the RNA polymerase, determining the sequence of nucleotides in the RNA strand. As a result, the RNA molecule, a copy of a portion of the DNA sequence, is produced and gradually elongated when the RNA polymerase moves along the DNA template.
Mechanism of RNA Synthesis during Elongation
During the elongation stage of RNA synthesis, the growing RNA chain is elongated by the addition of nucleotides to the 3′ end of the RNA strand. This process is catalyzed by the enzyme RNA polymerase.
1. Initiation of Elongation
- RNA polymerase binds to the promoter region of the DNA template.
- The enzyme unwinds the DNA and creates a transcription bubble.
- The first nucleotide of the RNA chain is added by complementary base pairing with the template strand.
2. Elongation of the RNA Chain
- RNA polymerase moves along the DNA template, using the template strand as a guide.
- Nucleotides from the nucleoside triphosphate pool bind to the template strand through complementary base pairing.
- The enzyme catalyzes the formation of a phosphodiester bond between the 3′-OH group of the growing RNA chain and the incoming nucleotide.
- The newly added nucleotide becomes the 3′ end of the RNA chain.
3. Proofreading and Repair
- RNA polymerase has a proofreading function to ensure the accuracy of RNA synthesis.
- If an incorrect nucleotide is added, the enzyme can hydrolyze the bond between the nucleotide and the growing RNA chain, removing the incorrect nucleotide.
- Other proteins, called repair enzymes, can also remove incorrect nucleotides from the RNA chain.
4. Termination of Elongation
- RNA synthesis terminates when the RNA polymerase reaches a specific termination sequence in the DNA template.
- The termination sequence signals the enzyme to release the newly synthesized RNA molecule from the template strand.
- The RNA molecule is then capped and polyadenylated to protect it from degradation.
Table: Steps of RNA Elongation
| Step | Description |
|---|---|
| 1 | Initiation |
| 2 | RNA polymerase binds to the promoter region of the DNA template. |
| 3 | The enzyme unwinds the DNA and creates a transcription bubble. |
| 4 | The first nucleotide of the RNA chain is added by complementary base pairing with the template strand. |
| 5 | Elongation |
| 6 | RNA polymerase moves along the DNA template, using the template strand as a guide. |
| 7 | Nucleotides from the nucleoside triphosphate pool bind to the template strand through complementary base pairing. |
| 8 | The enzyme catalyzes the formation of a phosphodiester bond between the 3′-OH group of the growing RNA chain and the incoming nucleotide. |
| 9 | The newly added nucleotide becomes the 3′ end of the RNA chain. |
| 10 | Termination |
| 11 | RNA synthesis terminates when the RNA polymerase reaches a specific termination sequence in the DNA template. |
| 12 | The termination sequence signals the enzyme to release the newly synthesized RNA molecule from the template strand. |
| 13 | The RNA molecule is then capped and polyadenylated to protect it from degradation. |
Question 1:
How does RNA synthesis occur during elongation?
Answer:
During elongation in RNA synthesis, RNA polymerase moves along the DNA template strand in the 5′ to 3′ direction.
Question 2:
Explain the role of ribosomes in RNA elongation.
Answer:
Ribosomes are cellular structures that bind to the mRNA template and facilitate the addition of complementary nucleotides by tRNA molecules.
Question 3:
What is the difference between leading and lagging strands in RNA elongation?
Answer:
As RNA polymerase elongates the RNA strand on the leading strand, it unwinds the DNA helix ahead of it. The lagging strand is synthesized in short fragments (Okazaki fragments) by a different polymerase that must wait for the leading strand to be unwound.
Well, there you have it, folks! Now you know a little bit more about how RNA is synthesized during elongation. Thanks for sticking with me through all the science jargon. I know it can be tough to understand at times, but I hope you found this article helpful. If you have any other questions about this topic or any other science-related topics, please don’t hesitate to ask. And be sure to check back later for more informative and hopefully less confusing articles. Until next time, stay curious and keep exploring the wonders of science!