Transcription as the Synthesis of RNA Using a DNA Template
Definition
Transcription
Transcription is the process by which the genetic information encoded in a DNA sequence is copied into a complementary RNA sequence.
- It is the first step in gene expression, where genetic information flows from DNA → RNA → Protein.
- The key enzyme in transcription is RNA polymerase, which performs multiple tasks to create an RNA strand.
Step by Step Breakdown Of Transcription
Transcription occurs in three stages: initiation, elongation, and termination.
Stage 1: Initiation
- Transcription begins when RNA polymerase binds to a promoter, a specific DNA region (shown in green in the diagram) that signals the start of a gene.
- The promoter acts as a recognition site, directing RNA polymerase to the correct location on the DNA.
Stage 2: Elongation
- RNA polymerase unwinds the DNA double helix, separating the two strands:
- Template strand (3' to 5'): Used to synthesize RNA.
- Coding strand (5' to 3'): Has the same sequence as the RNA (except RNA uses uracil instead of thymine).
- RNA polymerase moves along the template strand, adding RNA nucleotides one by one in the 5' to 3' direction (shown as the pink mRNA strand growing in the diagram).
- This process relies on complementary base pairing:
- Adenine (A) on the DNA template pairs with Uracil (U) in RNA.
