Lecture Notes: DNA Transcription and Translation

Overview

• Purpose: Understanding how DNA codes for organisms through transcription and translation.
• Key Concepts: Genetic code, transcription, translation, genes, proteins.

DNA Structure and Genes

• Chromosome: Long molecule with millions of base pairs.
• Genes: Special DNA portions coding for proteins.
  • Length varies, typically 10k-50k base pairs in humans.
  • Longest gene up to 2.5 million base pairs.

Transcription

• Definition: Process of converting DNA to mRNA using enzymes.
• Steps:
  • Initiation: RNA polymerase and transcription factors bind to the promoter sequence.
    • DNA strands are separated.
  • Elongation: RNA polymerase reads the antisense strand from 3' to 5'.
    • Synthesizes mRNA from 5' to 3'.
    • Uses ribose and uracil instead of deoxyribose and thymine.
  • Termination: RNA polymerase detaches after reaching the end of the gene.
• Outcome: mRNA carries genetic information from the gene.

RNA Processing

• Post-Transcriptional Modifications: mRNA undergoes modifications.
• Location: mRNA moves from nucleus to cytoplasm.

Translation

• Definition: mRNA is used to synthesize proteins.
• Codons:
  • Triplet groups of mRNA bases.
  • Each codon corresponds to specific anticodon on tRNA.
  • 64 possible codons from 4 bases, coding for amino acids.
  • Redundancy but no ambiguity in codon-amino acid mapping.
  • Start Codon: AUG (methionine).
  • Stop Codons: Three codons that terminate translation.

Translation Process

• Initiation:
  • Small ribosomal subunit binds to mRNA and initiator tRNA.
  • Large subunit forms the translation initiation complex.
• Elongation:
  • tRNA enters ribosome aligning with mRNA codon.
  • Amino acids covalently bond in sequence creating polypeptide chain.
• Termination:
  • Occurs at a stop codon.
  • Polypeptide released, enters cell organelles for folding and modification.

Importance

• Genes to Proteins: DNA transcribed to mRNA, mRNA translated to proteins.
• Proteins: Make up tissues, receptors, enzymes, fundamental to life.

• Conclusion: DNA is the blueprint for life, encoding the structure and function of living organisms through proteins.

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