Gene Structure and Regulation: Lac Operon Introduction

Review of Gene Structure and Transcription/Translation Basics

  • Gene Representation and Promoter Location: A gene is a specific sequence of DNA. While not always depicted, the promoter region, which signals the start of transcription, is located upstream of the gene (before the 5′5' end of the coding strand, or to the left on a typical diagram). For transcription to occur, the promoter must be recognized.

  • Coding vs. Template Strand for RNA Synthesis:

    • The coding strand (or sense strand) has a sequence identical to the mRNA transcript (with T instead of U). Looking at the coding strand makes it easier to determine the RNA sequence directly.

    • The template strand (or antisense strand) is read by RNA polymerase to synthesize the mRNA. If only the template strand is provided, one must first determine its complementary sequence to infer the RNA, which takes longer.

  • Untranslated Regions (UTRs):

    • 5′5' UTR (Untranslated Region): This sequence is at the beginning of the mRNA transcript but is not translated into protein. It's located between the 5′5' cap and the start codon (AUG).

    • 3′3' UTR (Untranslated Region): This sequence is at the end of the mRNA transcript, after the stop codon, and is also not translated into protein. (Reference to a