Transcription in prokaryotes

Summary

This video explains the process of transcription in prokaryotes, detailing the role of RNA polymerase in synthesizing RNA from DNA. It covers the enzyme’s structure, including its five subunits (beta prime, beta, alpha 1, alpha 2, and Omega), and the necessity of the Sigma factor for initiating transcription. The process is broken down into three stages: formation of the closed complex, the open complex, and abortive initiation. It also discusses two types of transcription termination: row-independent and row-dependent, with an emphasis on their mechanisms, including the formation of hairpin structures and the role of the row protein in termination.

Takeaways

• 😀 Transcription is enzymatically similar to DNA replication, with RNA polymerase synthesizing a complementary RNA strand, while DNA polymerase works with DNA.
• 😀 RNA polymerase has five subunits: beta prime, beta, alpha 1, alpha 2, and Omega, each with specific roles in RNA synthesis and enzyme assembly.
• 😀 The Sigma factor is essential for initiating transcription, helping RNA polymerase bind specifically to the promoter region of DNA.
• 😀 The RNA polymerase holoenzyme, which includes the Sigma factor, consists of six subunits in total.
• 😀 The initiation of transcription involves three steps: closed complex formation, open complex formation, and abortive initiation.
• 😀 In the closed complex, RNA polymerase binds to the double-stranded DNA promoter. In the open complex, the DNA unwinds near the transcription start site.
• 😀 Unlike DNA polymerase, RNA polymerase does not require a primer to begin transcription.
• 😀 Abortive initiation occurs when RNA polymerase creates short RNA stretches that are released due to the Sigma factor blocking the RNA exit channel.
• 😀 Elongation begins when the Sigma factor is released, and RNA polymerase continues to synthesize the RNA strand.
• 😀 Transcription termination in prokaryotes can be row-independent or row-dependent, with intrinsic terminators and the row factor playing key roles in the process.

Q & A

What is the main similarity between transcription and DNA replication?

Both transcription and DNA replication involve enzymes that synthesize new strands of nucleic acid complementary to a DNA template. However, the key difference lies in the type of nucleotides used: DNA polymerase adds deoxyribonucleic acids (dNTPs) during replication, while RNA polymerase adds ribonucleotides during transcription.

What is the role of RNA polymerase in transcription?

RNA polymerase is the enzyme responsible for synthesizing RNA during transcription. It binds to the DNA template and creates an RNA strand by adding ribonucleotides complementary to the DNA sequence.

What are the subunits of bacterial RNA polymerase?

Bacterial RNA polymerase consists of five subunits: beta prime, beta, alpha 1, alpha 2, and Omega. Beta prime is the largest subunit and contains the active site for RNA synthesis, while Omega helps in assembling and stabilizing the RNA polymerase.

What is the function of the Sigma factor in transcription?

The Sigma factor is a protein that assists RNA polymerase in binding to the promoter region of DNA. This binding is necessary for the initiation of transcription, and the Sigma factor ensures the specificity of RNA polymerase's interaction with the promoter.

What are the three main steps in the initiation of transcription?

The three steps in the initiation of transcription are: 1) formation of the closed complex (RNA polymerase binds to the promoter), 2) formation of the open complex (DNA strands unwind near the transcription start site), and 3) the phenomenon of abortive initiation (where RNA polymerase starts and releases short RNA stretches).

Why does RNA polymerase not require a primer to initiate transcription?

Unlike DNA polymerase, which requires a primer to begin DNA replication, RNA polymerase does not need a primer for transcription. It can initiate RNA synthesis directly at the promoter region of the DNA template.

What is abortive initiation in transcription?

Abortive initiation occurs when RNA polymerase synthesizes short RNA sequences that are released before elongation proceeds. This happens because the Sigma factor blocks the RNA exit channel of RNA polymerase, preventing the elongation process from starting immediately.

What happens during the elongation phase of transcription?

During elongation, once the Sigma factor is released, RNA polymerase moves along the DNA template, adding ribonucleotides to the growing RNA strand. This phase continues as long as RNA polymerase transcribes the gene.

What are the two modes of termination in bacterial transcription?

The two modes of termination in bacterial transcription are row-independent and row-dependent termination. Row-independent termination relies on the RNA's ability to form a hairpin structure that causes RNA polymerase to stop, while row-dependent termination requires the row protein to bind to the RNA and assist in releasing the RNA from the polymerase.

What is the role of the row protein in row-dependent termination?

The row protein is an ATP-dependent helicase that binds to single-stranded RNA rich in cytosine residues. It translocates along the RNA, unwinding the RNA-DNA hybrid, and helps release the RNA from the RNA polymerase to terminate transcription.