Transcription

This lesson covers transcription — the first stage of gene expression in which DNA is used as a template to synthesise messenger RNA (mRNA). Understanding transcription is essential for the Edexcel A-Level Biology specification (9BI0, Topic 7).

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What Is Transcription?

Transcription is the process by which the nucleotide sequence of the template strand of DNA is used to produce a complementary mRNA molecule. It takes place in the nucleus of eukaryotic cells.

Transcription is the first step in the central dogma of molecular biology:

DNA → mRNA → Protein

The central dogma can be visualised as follows:

graph LR
    A["DNA"] -->|"Transcription<br/>(RNA polymerase)"| B["mRNA"]
    B -->|"Translation<br/>(ribosomes)"| C["Protein"]
    A -->|"Replication<br/>(DNA polymerase)"| A

The enzyme responsible for catalysing transcription is RNA polymerase. In eukaryotes, RNA polymerase II is the enzyme that transcribes protein-coding genes.

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The Steps of Transcription

1. Initiation