Molecular Biology Chapter on Transcription

Learning Objectives

• Understand the transcription process of DNA into messenger RNA (mRNA) for protein synthesis.
• Describe transcription aspects: gene organization, transcription direction, transcription factors, and enzymes involved in prokaryotes and eukaryotes.
• Identify RNA modifications and the role of small nuclear ribonucleoproteins (snRNPs) in mRNA maturation.

Central Dogma of Molecular Biology

• Describes the flow of genetic information: DNA → RNA → Protein.
• Includes processes: replication, transcription, and translation.
• Highlights the importance of both transcriptional and translational control in gene expression.

Gene Expression

• Conversion of gene's coded information into functional cellular structures.
• Involves genes that are transcribed into mRNA, which may be translated into proteins, as well as those that produce non-coding RNAs (e.g., tRNA, rRNA).

Transcription in Bacteria

• Transcription requires RNA polymerase to synthesize mRNA from a DNA template.
• Consists of three phases: initiation, elongation, and termination.
• mRNA is synthesized in the 5' to 3' direction using the template strand of DNA.

Initiation of Transcription in Bacteria

• Begins at promoter regions (-35 box and -10 Pribnow box) where sigma subunit aids RNA polymerase binding.
• Opening of the DNA helix allows for mRNA synthesis.
• Sigma subunit dissociates once transcription begins.

Elongation and Termination in Bacterial Transcription

• The RNA polymerase core enzyme continues to add ribonucleotides to the growing mRNA strand.
• Termination occurs when RNA polymerase encounters a termination signal, leading to the formation of a hairpin loop in the RNA, causing polymerase to detach.

Eukaryotic Transcription Requirements

• Involves three types of RNA polymerases:
  • RNA polymerase I: Synthesizes rRNA.
  • RNA polymerase II: Synthesizes mRNA and non-coding RNAs (snRNA, miRNA).
  • RNA polymerase III: Synthesizes tRNA and some rRNA.
• Requires DNA template, transcription factors, and substrates (rNTPs).

Transcription Factors in Eukaryotes

• Essential for initiating and regulating transcription; classified as general and specific transcription factors.
• General transcription factors work with RNA polymerase to form the transcription initiation complex.
• Specific transcription factors modulate gene-specific transcription responses.

Transcription Process in Eukaryotes

• Cannot occur without RNA polymerase II binding to a promoter, facilitated by TFIID.
• Other factors, such as TFIIF and TFIIH, assist in transcription initiation and DNA unwinding.
• Genes are transcribed individually from their own promoters.

Clinical Significance

• α-amanitin (from Amanita phalloides) inhibits RNA polymerase II, affecting mRNA synthesis.
• Actinomycin D inhibits transcription by intercalating DNA, utilized in cancer treatment.

Post-Transcriptional Modifications

• Involves changes to pre-mRNA, including capping, polyadenylation, and splicing.
• snRNPs play a critical role in removing introns and maturing mRNA for translation.

This quiz focuses on key concepts in the molecular biology of gene expression, specifically the transcription phase. It covers the role of RNA polymerase, the arrangement of DNA, and the process of mRNA synthesis. Test your understanding of these fundamental biological processes!