Transcription and Translation Overview

Introduction

• Transcription: Process by which DNA is converted into mRNA (messenger RNA).
• Translation: Process of converting information from mRNA to synthesize proteins.
• Ribosome: The cellular organelle responsible for protein synthesis.

Transcription Process

1. Steps in Transcription:
   • Initiation: RNA polymerase binds to the promoter region of DNA.
     • Promoter Region: Short DNA sequence known as TATA box (TATAAA), located 25 nucleotides upstream of transcription start site.
   • Elongation: RNA polymerase adds nucleotides to growing mRNA strand.
     • Synthesizes mRNA from 5' to 3', while reading DNA from 3' to 5'.
     • Template (Anti-sense) Strand: Used by RNA polymerase to synthesize mRNA.
     • Sense (Coding) Strand: DNA strand not used in transcription.
   • Termination: RNA polymerase and mRNA separate from DNA.
     • Poly-A Tail: Added to 3' end of mRNA to prevent degradation.
     • 5' Cap: Added at the beginning to protect mRNA from enzymes.
     • RNA Splicing: Introns removed, exons remain to form mature mRNA.

Practice Problem

• DNA sequence to mRNA sequence conversion:
  • Read DNA 3' to 5' direction and write mRNA in 5' to 3'.
  • Base Pairing: G→C, C→G, A→U, T→A.

Translation Process

• mRNA to Protein Synthesis:
  • mRNA leaves nucleus, enters cytosol, interacts with ribosome.
  • mRNA codons match with tRNA anticodons to add specific amino acids.

1. Steps in Translation:
   • Initiation:
     • Start codon AUG (Methionine) binds to tRNA at P site in ribosome.
   • Elongation:
     • tRNA molecules enter at A site, and peptide bonds form between amino acids.
     • tRNA moves from P site to E site, loses amino acid, forms polypeptide chain.
   • Termination:
     • Stop codons (UAA, UAG, UGA) do not code for amino acids.
     • Release factors disassemble ribosome subunits, ending translation.
     • Protein moves to Golgi body for folding and functional shaping.

Conclusion

• Overview of transcription and translation processes.
• Essential understanding of molecular biology processes for protein synthesis.