Understanding the Process of Transcription

Sep 20, 2024

Lecture Notes: Transcription

Introduction

  • Transcription is unrelated to cell replication processes like DNA replication, mitosis, or cell division.
  • It is the first step in using the genetic code in DNA to synthesize proteins.

Importance of Transcription

  • DNA Location: Instructions for proteins are in DNA, located inside the nucleus.
  • Protein Synthesis Site: Proteins are made outside the nucleus in ribosomes (in cytoplasm or rough ER).
  • Function of Transcription: Transfers genetic code from DNA to ribosome via messenger RNA (mRNA).

Process of Transcription

  • Enzyme Involved: RNA polymerase attaches to a gene, a DNA segment containing protein-building code.
  • Structure of Genes: Genes have sequences of nitrogenous bases dictating amino acid order in proteins.
  • Codons: Groups of three bases in a gene code for specific amino acids, referred to as codons.

Steps in Transcription

  1. RNA Polymerase Action: Unwinds and separates DNA helix into two strands:
    • Template Strand: Read by mRNA.
    • Non-template Strand: Not transcribed.
  2. Base Pairing Rule: RNA polymerase assembles free nucleotides into RNA using the template strand:
    • Thymine in DNA pairs with Adenine in RNA.
    • Cytosine pairs with Guanine.
    • Guanine pairs with Cytosine.
    • Adenine pairs with Uracil (RNA contains uracil instead of thymine).

Completion of Transcription

  • mRNA Formation: mRNA is a complementary copy of the non-template DNA strand.
  • mRNA Transport: Small enough to exit nucleus via nuclear pore and travel to ribosome.

Protein Synthesis

  • Next Step: At ribosome, the actual protein-building process called translation occurs (covered separately).

Summary

  • Transcription: Copying genetic code for a protein into mRNA.
  • Gene: DNA segment with protein-building instructions.
  • Codon: Three-base group in a gene, coding for a specific amino acid.
  • RNA Polymerase: Unwinds DNA strands for transcription.
  • mRNA: Copy of DNA's non-template strand with uracil substituted for thymine.

Note: The detailed translation process, which follows transcription, will be covered separately.