Lecture Notes: Protein Synthesis

Introduction

• Topic: Protein synthesis
• Presenter: Miss Estrich
• Platform: Biology educational video

Overview of Protein Synthesis

• Purpose: Process where proteins are made, i.e., formation of a polypeptide chain or primary sequence of a protein.
• Location: Begins in the nucleus, primarily occurs on the ribosome.
• Stages:
  • Transcription: Occurs in the nucleus.
  • Translation: Occurs in the cytoplasm on ribosomes.

Details of Protein Synthesis

Transcription

• Location: Inside the nucleus.
• Purpose: To create a copy of the gene of interest because DNA cannot leave the nucleus and is vulnerable to cytoplasmic enzymes.
• Process:
  1. Unwinding of DNA: DNA helicase unwinds the DNA double helix, exposing two strands by breaking hydrogen bonds.
  2. Template Strand: One DNA strand acts as a template to make mRNA (single-stranded).
  3. Complementary Base Pairing: Free RNA nucleotides pair with complementary DNA bases.
  4. RNA Polymerase: Joins nucleotides together by phosphodiester bonds.
  5. Formation of pre-mRNA: Needs modification before leaving the nucleus.
  6. Splicing: Removal of introns (non-coding regions) by spliceosome, leaving exons (coding regions).

Translation

• Location: In the cytoplasm.
• Purpose: Creation of a polypeptide chain (primary sequence of a protein).
• Process:
  1. Attachment to Ribosome: Modified mRNA attaches to a ribosome at the start codon (first three mRNA bases).
  2. Role of tRNA: Each tRNA, with an anticodon, brings a specific amino acid.
  3. Complementary Pairing: tRNA anticodon pairs with mRNA codon.
  4. Peptide Bond Formation: Amino acids linked by peptide bonds, requiring an enzyme and ATP.
  5. Ribosome Movement: Moves along mRNA, aligning tRNA with matching anticodons.
  6. Stop Codon: Translation ends when ribosome reaches stop codon (last three bases on mRNA).
  7. Detachment: Ribosome detaches, releasing finished polypeptide chain.

Conclusion

• Protein Synthesis Result: Formation of primary sequence of protein.
• Further Processing: Polypeptide chain undergoes folding/modifications in the Golgi body to form the final protein structure.
• Further Learning: Links to related videos on RNA and genetic code.

• Note: For more insights on alternative splicing and why DNA has non-coding regions, additional research is suggested as it's not covered in AQA specification.

End of Notes