RNA polymerase

Definition

RNA polymerase is an enzyme that synthesizes RNA from a DNA template during the process of transcription. It plays a crucial role in converting genetic information stored in DNA into RNA, which is necessary for protein synthesis and gene expression regulation. This enzyme interacts with various transcription factors and is essential for the transcription process in both prokaryotic and eukaryotic organisms.

5 Must Know Facts For Your Next Test

1. RNA polymerase catalyzes the addition of ribonucleotides to the growing RNA strand during transcription, following base-pairing rules with the DNA template.
2. In prokaryotes, a single type of RNA polymerase is responsible for synthesizing all types of RNA, while eukaryotes have three different RNA polymerases, each responsible for transcribing different classes of genes.
3. RNA polymerase requires various transcription factors to help it bind to the promoter region of genes, facilitating the initiation of transcription.
4. The enzyme not only synthesizes RNA but also proofreads the RNA strand as it is being formed to ensure accuracy.
5. Once transcription is complete, RNA polymerase detaches from the DNA and releases the newly synthesized RNA molecule for further processing or translation.

Review Questions

• How does RNA polymerase initiate transcription in prokaryotic cells, and what role do promoters play in this process?
  • In prokaryotic cells, RNA polymerase initiates transcription by binding to a specific region called the promoter located upstream of a gene. The promoter contains sequences that are recognized by the RNA polymerase and associated sigma factors, which help guide the enzyme to the correct start site. Once bound to the promoter, RNA polymerase unwinds the DNA helix and begins synthesizing RNA complementary to the DNA template strand.
• Discuss the differences in RNA polymerase function between prokaryotic and eukaryotic cells, focusing on their roles in transcription.
  • In prokaryotic cells, there is a single type of RNA polymerase that synthesizes all forms of RNA, including mRNA, tRNA, and rRNA. In contrast, eukaryotic cells have three distinct RNA polymerases: RNA polymerase I transcribes rRNA (excluding 5S rRNA), RNA polymerase II transcribes mRNA and some snRNA, while RNA polymerase III transcribes tRNA and other small RNAs. Eukaryotic RNA polymerases also require a more complex set of transcription factors for initiation compared to their prokaryotic counterpart.
• Evaluate the importance of RNA polymerase in gene regulation and expression, particularly in eukaryotic systems.
  • RNA polymerase plays a vital role in gene regulation and expression in eukaryotic systems by being influenced by various transcription factors that bind to enhancers or silencers located far from the gene. These interactions facilitate or inhibit the assembly of the transcription machinery at promoters. Additionally, post-transcriptional modifications such as capping, polyadenylation, and splicing, which occur after initial transcription by RNA polymerase II, are essential for producing functional mRNA. Thus, the regulation of RNA polymerase activity directly impacts gene expression and cellular function.

Related terms

Transcription: The process by which RNA is synthesized from a DNA template, resulting in the formation of messenger RNA (mRNA), which carries genetic information to ribosomes.

Promoter:

A specific DNA sequence located upstream of a gene that serves as a binding site for RNA polymerase and initiates the transcription process.

Ribosome: A cellular structure that facilitates the translation of mRNA into a polypeptide chain, ultimately forming proteins.