6.Prokaryotic gene transcription, its steps, enzymes involved in its mechanism
Prokaryotic gene transcription is the process by which the genetic information encoded in DNA is transcribed into RNA molecules. This process occurs in the cytoplasm of prokaryotic cells and is essential for protein synthesis.
The steps involved in prokaryotic gene transcription are as follows:
1. Initiation: The first step in gene transcription is initiation. The RNA polymerase enzyme binds to a specific DNA sequence called the promoter region, which is located upstream of the gene to be transcribed. The RNA polymerase unwinds and separates the DNA strands, creating a transcription bubble.
2. Elongation: Once the RNA polymerase has bound to the promoter region, it moves along the DNA template strand in the 3' to 5' direction, synthesizing an RNA molecule in the 5' to 3' direction. As it moves, the RNA polymerase adds complementary RNA nucleotides that are base-paired with the exposed DNA template strand.
3. Termination: The final step in gene transcription is termination. In prokaryotes, there are two types of termination: Rho-dependent and Rho-independent termination. In Rho-dependent termination, a protein called Rho binds to the newly synthesized RNA molecule, causing the RNA polymerase to dissociate from the DNA template strand. In Rho-independent termination, specific DNA sequences on the RNA molecule form a hairpin loop followed by a string of uracil bases, which destabilizes the RNA-DNA hybrid and leads to RNA polymerase dissociation.
The enzymes involved in the mechanism of prokaryotic gene transcription include:
1. RNA polymerase: This enzyme is responsible for synthesizing RNA molecules from a DNA template. It binds to the promoter region and catalyzes the addition of RNA nucleotides to the growing RNA chain.
2. Sigma factor: In prokaryotes, RNA polymerase is associated with a sigma factor, which helps the enzyme recognize and bind to the promoter region on the DNA template strand.
3. Rho protein: This protein is involved in Rho-dependent termination. It binds to the newly synthesized RNA molecule and causes the RNA polymerase to dissociate from the DNA template.
Overall, prokaryotic gene transcription is a complex process that involves the interaction of various enzymes, such as RNA polymerase, sigma factor, and rho protein, to ensure accurate and efficient synthesis of RNA molecules from DNA templates.
Prokaryotic gene transcription is the process by which genetic information stored in DNA is copied into RNA molecules. The steps involved in prokaryotic gene transcription are initiation, elongation, and termination. Let's go through each step and discuss the enzymes involved in each mechanism.
1. Initiation:
- RNA polymerase: The enzyme responsible for initiating transcription. In prokaryotes, there is only one type of RNA polymerase that catalyzes the entire transcription process. It binds to the promoter region of the DNA, which marks the starting point for transcription.
- Promoter region: A specific DNA sequence located upstream (before) the gene, which signals the RNA polymerase to bind and start transcription.
2. Elongation:
- RNA polymerase: After binding to the promoter, RNA polymerase unwinds the DNA double helix and starts synthesizing the RNA molecule. It moves along the DNA template strand in a 3' to 5' direction while adding RNA nucleotides in a complementary manner to the DNA template.
3. Termination:
- Termination signal: A specific DNA sequence that signals the end of transcription. In prokaryotes, there are two types of termination signals: intrinsic termination and rho-dependent termination.
- Intrinsic termination: In this mechanism, a termination sequence in the DNA template strand causes the newly synthesized RNA to fold back on itself, forming a hairpin loop. This destabilizes the RNA-DNA hybrid, leading to the release of RNA polymerase and termination of transcription.
- Rho-dependent termination: This mechanism involves the Rho protein. It binds to the growing RNA molecule and helps dislodge the RNA polymerase from the DNA template, leading to termination.
So, in summary, the key enzymes involved in prokaryotic gene transcription are RNA polymerase, which carries out initiation, elongation, and termination of transcription, and the Rho protein for rho-dependent termination.
Prokaryotic gene transcription is the process by which genetic information in prokaryotic cells is copied from DNA to mRNA. It involves several steps and the involvement of different enzymes. Let's go through each step and the enzymes involved in this process:
1. Initiation:
- The first step is the binding of RNA polymerase to the promoter region of the DNA.
- The RNA polymerase recognizes the specific sequence of DNA called the promoter and binds to it.
- The enzyme responsible for this binding is the RNA polymerase holoenzyme, which consists of a core enzyme and a sigma factor.
2. Promoter Clearance:
- Once the RNA polymerase is bound to the promoter, it initiates the separation of DNA strands, forming a transcription bubble.
- The sigma factor helps in the separation of the strands.
- In this step, the RNA polymerase also synthesizes a short RNA primer that is complementary to the DNA template strand.
3. Elongation:
- After the promoter clearance, the RNA polymerase moves along the DNA template strand in a 3' to 5' direction.
- It adds complementary RNA nucleotides to the growing RNA chain in a 5' to 3' direction.
- The enzyme responsible for building the RNA chain is the RNA polymerase itself.
4. Termination:
- The termination of transcription occurs when the RNA polymerase reaches a specific termination sequence in the DNA template strand.
- There are two types of termination: intrinsic termination and rho-dependent termination.
- In intrinsic termination, the termination sequence contains a specific region called a termination hairpin, which causes the RNA polymerase to pause and eventually release the RNA transcript.
- In rho-dependent termination, an additional protein called the rho factor is involved. The rho factor tracks along behind the RNA polymerase and aids in the termination process.
In summary, the key enzymes involved in prokaryotic gene transcription are the RNA polymerase holoenzyme, RNA polymerase itself, and the sigma factor. These enzymes work together to initiate transcription, clear the promoter, elongate the RNA chain, and eventually terminate transcription at specific sequences in the DNA template strand.