Lecture Notes: DNA Transcription and Translation

Introduction

• Topic: Understanding how DNA codes for a particular organism
• Processes: Transcription and translation
• Purpose: To produce all proteins in an organism by reading the genetic code

DNA and Genes

• Chromosome: Long molecule with many base pairs
• Gene: Specific part of a chromosome that codes for proteins
  • Average length: 10,000 to 50,000 base pairs
  • Longest gene: 2.5 million base pairs

Transcription

• Definition: Process of producing mRNA from DNA
• Key Enzyme: RNA polymerase
• Process:
  1. Binding: RNA polymerase binds to promoter sequence on DNA with help of transcription factors
  2. Strand Separation: DNA strands are pried apart
  3. Template Strand (Antisense Strand): Used to generate mRNA
  4. Nontemplate Strand (Sense Strand): Not used for mRNA
  5. Synthesis Initiation: Begins at start codon
  6. Elongation: RNA polymerase moves along gene, synthesizing mRNA
  7. Termination: RNA polymerase detaches, DNA returns to original state
• Differences from DNA Replication:
  • RNA has ribose and uracil instead of deoxyribose and thymine
  • DNA is re-zipped as mRNA is synthesized

mRNA Processing and Translation

• mRNA Processing: Modifications before leaving nucleus
• Translation Location: Occurs in ribosomes in the cytoplasm

Translation

• Process:
  1. Initiation: mRNA binds to small ribosomal subunit, initiator tRNA binds to start codon
  2. Large Subunit Binding: Completes initiation complex
  3. Codon Reading: Each mRNA codon codes for tRNA anticodon
  4. Amino Acid Linkage: Amino acids linked to form polypeptide chain
  5. Termination: Occurs at stop codon, completed polypeptide released

Genetic Code

• Codons: Sets of three bases on mRNA
  • 64 possible codons (4 bases, 3 letters each)
  • Redundancy: Multiple codons for same amino acid, no ambiguity
  • Special codons:
    • Start Codon: AUG (Methionine)
    • Stop Codons: Terminate translation

Conclusion

• Outcome: DNA transcribed to mRNA, then translated to proteins
• Importance: Proteins make up muscle tissue, organ tissue, receptors, enzymes
• DNA's Role: Carries the genetic code for living organisms

Miscellaneous

• Contact: Professor Dave encourages subscribing to his channel and reaching out via email for more tutorials.