Lecture on Transcription and Translation: DNA to RNA to Protein

Introduction to Genes and Traits

• Genes: Instructions for traits; genetic material is DNA.
• DNA: Blueprint for organism characteristics (e.g., eye color, height, freckles).
• Polypeptides: Form from DNA; a polymer for protein leading to functional proteins.
• Protein Structure: Shape determines function, like a wheel rolls due to its round shape.

Gene Expression

• Molecular Function: Operation at the protein level (e.g., sodium-potassium production).
• Phenotype: External traits (e.g., brown hair, long nails).
• Types of Genes:
  • Protein-Coding Genes: Create polypeptides.
  • Non-Coding RNAs: Don't create polypeptides but are crucial for DNA structure.

Central Dogma of Biology

• DNA → RNA → Protein
• Transcription: Process from DNA to RNA.
  • Analogy: Recipe book (DNA) to specific recipe (RNA).
• Translation: RNA to protein; making an actual product (e.g., pie vs. recipe).

Transcription in Eukaryotes vs. Prokaryotes

• Eukaryotes: More complex, includes RNA processing.
  • Transcription: DNA in nucleus transcribes to RNA, undergoes RNA processing.
  • Translation: Process occurs in cytosol using ribosomes.
• Prokaryotes: Simpler process, all occurs in the cytosol without organelles.

Details of Transcription

• RNA Transcript: The copied RNA from a gene.
• RNA Types:
  • mRNA: Messenger RNA, carries the protein-making recipe.
  • tRNA: Transfer RNA, carries amino acids for translation.
  • rRNA: Ribosomal RNA, forms the ribosome structure.

Components of DNA for Transcription

• Promoter: Start site for transcription.
• Terminator: End site for transcription.
• Regulatory Sequences: Control transcription initiation.
• RNA Polymerase: Enzyme that synthesizes RNA.

Transcription Process in Bacteria

• Initiation: Sigma factor binds RNA polymerase to promoter, forming open complex.
• Elongation: RNA polymerase synthesizes RNA using DNA template strand.
  • Template Strand: Guides RNA synthesis; Coding Strand: Matches new RNA sequence.
• Termination: RNA polymerase reaches terminator, RNA transcript separates.

Eukaryotic Transcription

• Similar to prokaryotic but includes more steps and enzymes.
• RNA Polymerase Types:
  • RNA Polymerase II: Transcribes mRNA.
  • RNA Polymerase I & III: Transcribe non-structural genes.

RNA Processing (Eukaryotes)

• Pre-mRNA: Initial transcription product, includes introns and exons.
• Splicing: Removal of introns, leaving exons.
  • Introns: Non-coding sequences.
  • Exons: Coding sequences kept for protein synthesis.
• 5' Cap and 3' Poly-A Tail: Modify mRNA for stability and protection.

Conclusion

• Understanding of transcription and translation is crucial for grasping gene expression and protein synthesis.
• Different cellular processes and components play roles in expressing genetic information into functional proteins.