Lecture Notes on Protein Synthesis

Introduction

• Protein Synthesis Overview
  • The process of creating proteins, specifically the formation of the polypeptide chain.
  • Occurs primarily on the ribosome and involves two main stages: transcription and translation.

Transcription

• Location: Occurs inside the nucleus.
• Purpose: To create a copy of a gene into messenger RNA (mRNA) because DNA is too large to leave the nucleus.
• Process: Key Steps
  1. DNA Unwinding:
     • DNA double helix unwinds, exposing two strands.
     • One strand acts as the template for mRNA.
  2. DNA Helicase:
     • Enzyme that breaks hydrogen bonds between DNA strands.
  3. RNA Nucleotides Alignment:
     • Free RNA nucleotides align with complementary DNA bases.
  4. RNA Polymerase:
     • Joins nucleotides together forming phosphodiester bonds.
     • Resulting strand is called pre-mRNA.
  5. Splicing:
     • Introns (non-coding sequences) are removed by spliceosome.
     • Results in mRNA formed of only exons (coding sequences).

Translation

• Location: Occurs in the cytoplasm.
• Purpose: To synthesize the polypeptide chain using mRNA and transfer RNA (tRNA).
• Process: Key Steps
  1. mRNA Attachment:
     • Modified mRNA exits nucleus and binds to ribosome at start codon.
  2. tRNA Function:
     • Each tRNA molecule has an anticodon and an amino acid attachment site.
     • Correct tRNA aligns with complementary mRNA codon.
  3. Ribosome Function:
     • Holds mRNA and tRNA in place for amino acid transfer.
  4. Peptide Bond Formation:
     • Amino acids from tRNA join via peptide bonds (requires enzyme and ATP).
  5. Ribosome Movement:
     • Ribosome shifts along mRNA, facilitating formation of peptide bonds between successive amino acids.
  6. Termination:
     • Stop codon on mRNA signals end of translation.
     • Ribosome detaches, releasing the polypeptide chain.

Post-Translation: Protein Folding

• Polypeptide chain undergoes folding and modifications at the Golgi body to form the final functional protein.

Conclusion

• Summary: Protein synthesis is essential for forming proteins, involving transcription and translation processes.
• Final Note: Understanding protein synthesis is crucial for higher-level biology topics.

Additional Resources: Links to videos mentioned in the lecture for further understanding of RNA and genetic code intricacies.