RNA Transcription: Process and Stages
RNA Transcription: A Detailed Look
Transcription is the process of RNA synthesis, which occurs inside the cell nucleus. This process requires:
- A DNA strand that acts as a template.
- RNA polymerase (RNA-pol) enzyme.
- Ribonucleotide triphosphates (A, G, C, and U).
Ribonucleotides are linked via phosphodiester bonds. The overall process consists of three main stages: initiation, elongation, and termination.
Initiation
RNA polymerase recognizes specific sequences in the DNA that will be transcribed. These sequences signal the start of transcription and are known as promoter sites. The process involves these steps:
- Short sequences of nitrogenous bases are recognized.
- Helicase, an enzyme, causes the DNA double helix to unwind and open.
- This exposes the DNA bases.
- Ribonucleotides begin to bind to the exposed bases.
Elongation
During elongation, successive ribonucleotides are added to form the growing RNA chain. Key points about elongation:
- RNA polymerase “reads” the DNA template strand in the 3′ to 5′ direction.
- RNA synthesis occurs in the 5′ to 3′ direction.
- The synthesized RNA chain is complementary to the DNA template strand.
Termination
RNA polymerase recognizes a termination signal in the DNA, indicating the end of transcription. Termination involves:
- The closure of the “bubble” formed in the DNA.
- Separation of the RNA molecule from the RNA polymerase and the DNA template.
Post-transcriptional Modifications
- 3′ End: A sequence of adenine ribonucleotides (poly-A tail) is added.
- 5′ End: A cap is added, making it possible to identify the RNA molecule in the subsequent translation process.
Transcription is the process of RNA synthesis, which occurs inside the cell nucleus. This process requires:
- A DNA strand that acts as a template.
- RNA polymerase (RNA-pol) enzyme.
- Ribonucleotide triphosphates (A, G, C, and U).
Ribonucleotides are linked via phosphodiester bonds. The overall process consists of three main stages: initiation, elongation, and termination.
Initiation
RNA polymerase recognizes specific sequences in the DNA that will be transcribed. These sequences signal the start of transcription and are known as promoter sites. The process involves these steps:
- Short sequences of nitrogenous bases are recognized.
- Helicase, an enzyme, causes the DNA double helix to unwind and open.
- This exposes the DNA bases.
- Ribonucleotides begin to bind to the exposed bases.
Elongation
During elongation, successive ribonucleotides are added to form the growing RNA chain. Key points about elongation:
- RNA polymerase “reads” the DNA template strand in the 3′ to 5′ direction.
- RNA synthesis occurs in the 5′ to 3′ direction.
- The synthesized RNA chain is complementary to the DNA template strand.
Termination
RNA polymerase recognizes a termination signal in the DNA, indicating the end of transcription. Termination involves:
- The closure of the “bubble” formed in the DNA.
- Separation of the RNA molecule from the RNA polymerase and the DNA template.
Post-transcriptional Modifications
- 3′ End: A sequence of adenine ribonucleotides (poly-A tail) is added.
- 5′ End: A cap is added, making it possible to identify the RNA molecule in the subsequent translation process.
Transcription is the process of RNA synthesis, which occurs inside the cell nucleus. This process requires:
- A DNA strand that acts as a template.
- RNA polymerase (RNA-pol) enzyme.
- Ribonucleotide triphosphates (A, G, C, and U).
Ribonucleotides are linked via phosphodiester bonds. The overall process consists of three main stages: initiation, elongation, and termination.
Initiation
RNA polymerase recognizes specific sequences in the DNA that will be transcribed. These sequences signal the start of transcription and are known as promoter sites. The process involves these steps:
- Short sequences of nitrogenous bases are recognized.
- Helicase, an enzyme, causes the DNA double helix to unwind and open.
- This exposes the DNA bases.
- Ribonucleotides begin to bind to the exposed bases.
Elongation
During elongation, successive ribonucleotides are added to form the growing RNA chain. Key points about elongation:
- RNA polymerase “reads” the DNA template strand in the 3′ to 5′ direction.
- RNA synthesis occurs in the 5′ to 3′ direction.
- The synthesized RNA chain is complementary to the DNA template strand.
Termination
RNA polymerase recognizes a termination signal in the DNA, indicating the end of transcription. Termination involves:
- The closure of the “bubble” formed in the DNA.
- Separation of the RNA molecule from the RNA polymerase and the DNA template.
Post-transcriptional Modifications
- 3′ End: A sequence of adenine ribonucleotides (poly-A tail) is added.
- 5′ End: A cap is added, making it possible to identify the RNA molecule in the subsequent translation process.