Notes on Translation in Molecular Biology

Introduction to Translation

• Overview of the Central Dogma of Molecular Biology
  • DNA replication leads to the transcription of DNA into mRNA, which is then translated into proteins (polypeptide chains of amino acids).

Understanding tRNA vs. mRNA

• mRNA (messenger RNA):
  • Carries the genetic blueprint from DNA for protein synthesis.
• tRNA (transfer RNA):
  • Transports specific amino acids to the ribosome based on the mRNA sequence. Each tRNA has an anticodon complementary to mRNA codons.

The Genetic Code

• Comprised of codons (triplet codes) which specify amino acids.
• Codons:
  • 64 possible codons (from combinations of the 4 nucleotides) but only 20 amino acids, indicating code degeneracy.
  • Allows for silent mutations where changes in codons may not affect amino acid sequence.

Protein Structure Levels

• Primary Structure:
  • Sequence of amino acids in a polypeptide chain.
• Secondary Structure:
  • Local folding into structures such as alpha-helixes and beta-sheets.
• Tertiary Structure:
  • Overall 3D shape of a polypeptide.
• Quaternary Structure:
  • Interaction of multiple polypeptides to form a functional protein.

Key Components in Translation

• Translation Machinery:
  • Ribosomes (composed of rRNA and proteins).
  • tRNA molecules, charged by tRNA synthetases.
• Binding Sites in Ribosomes:
  • A site: Holds the tRNA with the next amino acid.
  • P site: Holds the tRNA with the polypeptide chain.
  • E site: Exit site for tRNA.

Stages of Translation

• Initiation:

  • mRNA binds to the ribosome; the start codon (AUG) signifies where translation begins.
  • Prokaryotic Initiation: Involves the Shine-Dalgarno sequence which aligns mRNA with the ribosome.
  • Eukaryotic Initiation: Uses a 5' cap followed by scanning for AUG using Kozak's rule.

• Elongation:

  • Sequential addition of amino acids to the growing polypeptide chain.
  • Peptide bonds are formed between amino acids via a condensation reaction.

• Termination:

  • Occurs when a stop codon (UAG, UAA, UGA) is reached.
  • Release factors facilitate the release of the newly synthesized polypeptide and disassemble the ribosome.

Importance of Sequences in Translation

• Recognition of key sequences (start and stop codons) is crucial in both prokaryotes and eukaryotes for initiating and terminating translation.
• Essential for understanding the relationships between DNA, mRNA, and the resulting polypeptide chain.

Summary

• The final product of translation is a polypeptide that folds into a protein, driven by the genetic code provided by mRNA.
• Recall the roles of mRNA, tRNA, and ribosomes in the process, as well as the significance of the sequences involved.