LEC 5 NOTES CELL BIO LEC

Transcription Overview

  • Transcription is the process of creating an RNA copy from a section of DNA.

  • This process is crucial for gene expression in eukaryotic cells.

Initiation of Transcription

  • Begins when several factors gather at the start of a gene.

  • The TBP (TATA-binding protein) subunit of the TF2D complex binds to a gene's promoter, particularly at the TATA box.

  • The gene to be transcribed extends to the left of the promoter in the visual representation.

  • Other general transcription factors assemble alongside RNA polymerase II, forming a complete transcription initiation complex.

Role of General Transcription Factors

  • TF2H is one of the general transcription factors that plays a crucial role in opening the DNA strands at the start site of transcription.

  • This exposure is necessary for RNA polymerase to access the DNA template strand.

  • The orientation of the promoter determines which DNA strand will serve as the template, as RNA polymerase can only synthesize RNA in the 5' to 3' direction.

  • Transcriptional regulators can interact with cis-regulatory DNA sequences, potentially located far (up to tens of thousands of nucleotides) from the core promoter.

Regulation of Transcription

  • A distal enhancer, when bound by its activator, can loop around to interact with the initiation complex, facilitating the activation of RNA transcription.

  • Upon activation, RNA polymerase is released from the general transcription factors and undergoes conformational changes that allow it to proceed to the elongation phase.

Elongation Phase of Transcription

  • As the RNA polymerase moves away from the promoter, it synthesizes RNA.

  • The RNA strand, which is a copy of the genetic information, exits at the top of the polymerase.

  • RNA polymerase unwinds the DNA's double helix, allowing ribonucleotide building blocks to enter through an intake pore.

  • These building blocks are then used to construct a complementary RNA transcript, copied nucleotide by nucleotide, from the DNA template strand.

  • Notably, the ribonucleotide base Uracil (U) is used in place of Thymine (T), which is found in DNA.

Visual Representation

  • The video displays the transcription process in near real-time, illustrating the dynamics of RNA synthesis and polymerase function during transcription.