Lecture Notes: DNA Transcription and Translation

Introduction

• Topic: DNA transcription and translation
• Purpose: Understanding how DNA codes for organisms

Key Concepts

1. Genetic Code: DNA is read by enzymes to produce proteins
2. Chromosomes: Long molecules with base pairs, containing genes
3. Genes: Portions of DNA that code for proteins

Transcription Process

• Definition: Enzymes use DNA as a template to produce mRNA
• RNA Polymerase Role:
  • Binds to promoter sequence
  • Separates the DNA strands
  • Uses the template (antisense) strand to synthesize mRNA
  • Moves downstream, reading from 3' to 5', creating mRNA from 5' to 3'
  • Synthesizes mRNA with ribose and uracil instead of deoxyribose and thymine
  • Zips DNA back up as it goes
  • Detaches at termination, releasing mRNA

RNA Processing

• mRNA undergoes modifications before leaving the nucleus

Translation Process

• Definition: mRNA serves as a code for protein synthesis
• Codons: Triplets of bases on mRNA, each coding for an anticodon on tRNA
• tRNA:
  • Carries specific amino acids
  • Matches anticodons with mRNA codons
• Reading Frame: Arrangement of nucleotides into codons (64 possibilities due to 4 bases)
  • Redundancy exists, but no ambiguity
  • Special Codons: AUG (start), stop codons

Ribosome Function in Translation

• Small Ribosomal Subunit: Binds to mRNA and initiator tRNA
• Large Ribosomal Subunit: Completes the initiation complex
• Process:
  • tRNA's enter and exit, adding amino acids to growing polypeptide chain
  • Continues until stop codon is reached
  • Polypeptide is released and undergoes further folding/modification

Conclusion

• Two-Step Process: DNA is transcribed to mRNA, which is translated into protein
• Significance: DNA codes for the proteins that make up living organisms

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