U01.01.010 Functional organization of a eukaryotic gene

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Learning Objectives

  • Identify the regulatory regions of a eukaryotic gene (Promoters, Enhancers, Silencers).
  • Distinguish between Exons and Introns during RNA processing.
  • Locate critical signaling sequences such as the TATA box and Polyadenylation signal.
  • Trace the flow of information from DNA to Mature mRNA to Protein.

1. DNA Regulatory Regions

The control of transcription involves specific DNA sequences located both near and far from the transcription start site.

  • Promoter: The region where RNA polymerase II and transcription factors bind. Contains the TATA box (TATAAA) and often a CAAT box.
  • Enhancers: DNA sequences that increase the rate of transcription. They can be located far upstream or downstream.
  • Silencers: DNA sequences that decrease the rate of transcription by binding repressor proteins.

2. The Open Reading Frame (ORF)

The ORF contains the actual instructions for the protein, but it is interrupted by non-coding segments in eukaryotes.

Component Description
Exons Coding regions that are Expressed. They remain in the mature mRNA.
Introns Non-coding regions that Intervene. They are spliced out.
5′ & 3′ UTR Untranslated Regions. They are transcribed but not translated; involved in mRNA stability and translation regulation.

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3. Transcription & RNA Processing

  • Transcription Start: Initiates at the 5′ end. The sequence begins with a 5′ Cap (added post-transcriptionally).
  • Splicing: Occurs at specific junctions. Introns usually begin with GU and end with AG (at the RNA level).
  • Polyadenylation: The Poly-A tail is added to the 3′ end following the AAUAAA consensus signal. This protects mRNA from degradation.

4. Translation Summary

  • Start Codon: AUG (Methionine in eukaryotes).
  • Stop Codons: UGA, UAA, or UAG. These terminate the peptide chain.

 

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