Transcription

Introduction

• Transcription is a vital process in gene expression.
• It involves the conversion of the genetic information encoded in DNA into a complementary RNA molecule, specifically mRNA (messenger RNA).

1. Initiation of Transcription

• Transcription begins in the nucleus when a gene needs to be expressed.
• RNA polymerase, an enzyme, initiates the process by binding to the DNA molecule at the gene's start site.

2. Unwinding the DNA Strand

• As RNA polymerase moves along the DNA strand, it unwinds the double helix.
• This unwinding process is crucial for exposing the DNA sequence to be transcribed.

3. Breaking Hydrogen Bonds

• Hydrogen bonds between the base pairs of DNA break as a result of the unwinding.
• This breaking of bonds allows the separation or unzipping of the two DNA strands.

4. Synthesis of Primary Transcript

• RNA polymerase synthesises a primary transcript of mRNA.
• This synthesis involves adding RNA nucleotides to the growing RNA strand.
• RNA nucleotides form hydrogen bonds with the exposed DNA strand, following the complementary base pairing rule (A-U and C-G).

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Transcription

5. Processing the Primary Transcript

• The primary transcript of mRNA may undergo post-transcriptional modifications.
• These modifications include the removal of introns (non-coding regions) and the addition of a 5' cap and a poly-A tail.
• These modifications result in the production of a mature transcript of mRNA.

6. Ready for Translation

• The mature mRNA transcript is now ready to leave the nucleus and travel to the ribosome.
• It carries the genetic information from the gene to the ribosome, where protein synthesis or translation will occur.

Summary

Transcription is the process of converting DNA into mRNA. It begins with the initiation of RNA polymerase at the gene's start site. The DNA strand is unwound, and hydrogen bonds break to expose the DNA sequence. RNA polymerase synthesises a primary transcript of mRNA, which may undergo post-transcriptional modifications to become a mature transcript. The mature mRNA molecule then leaves the nucleus and heads to the ribosome, where protein synthesis takes place. Transcription is a crucial step in gene expression and the production of functional proteins in cells.