Lecture Notes on Protein Synthesis: Transcription

Overview of Protein Synthesis

• Protein Synthesis: Process of creating polypeptides (proteins) from DNA.
• Two Main Processes:
  1. Transcription: Gene is transcribed to produce mRNA.
  2. Translation: mRNA goes to ribosome; tRNA carries amino acids to form polypeptides.

Focus on Transcription

• Transcription Definition: Copying of a gene to produce mRNA.
• Gene and DNA Structure:
  • Genes are sections of DNA, which is double-stranded.
  • mRNA is single-stranded.

Process of Transcription

• Gene Unwinding: Only the specific section of DNA with the gene unwinds (unlike entire DNA unwinding in replication).
• Template Strand:
  • Only one DNA strand (template strand) is used.
  • Non-template strand is not used.
• Base Pairing:
  • RNA nucleotides pair with the DNA template strand.
  • Base Pairing Rules:
    • DNA base T pairs with RNA base A.
    • DNA base A pairs with RNA base U (uracil replaces thymine in RNA).

Example Base Sequences

• DNA Template: TAC-GGC-TTC-AAG-CGC-GCT-ACT
• Corresponding RNA Sequence: AUG-CCG-AAG-UUC-GCG-CGA-UGA

Role of RNA Polymerase

• RNA Polymerase: Enzyme that joins RNA nucleotides.
  • Functions similarly to DNA polymerase in DNA replication.
  • Moves along template strand and synthesizes mRNA from 5’ to 3’ direction.

Final Steps of Transcription

• mRNA Detachment:
  • Newly synthesized mRNA detaches from the template strand.
• DNA Reformation:
  • DNA rewinds into its original double-stranded form.