Biology: Translation in Protein Synthesis

Translation

• Translation is the process by which genetic information encoded in mRNA is used to synthesize proteins.
• This process takes place in the ribosomes, which are the cellular structures responsible for protein synthesis.
• Translation is the second step in the central dogma of molecular biology.

Stages of Translation

• Initiation: mRNA binding, start codon recognition, tRNA binding, and formation of initiation complex.
  • mRNA binding: The small subunit of the ribosome binds to the mRNA near its 5’ end.
  • Start codon recognition: The start codon (AUG) on the mRNA is recognized, which codes for the amino acid methionine.
  • tRNA binding: A specific initiator tRNA carrying methionine binds to the start codon through complementary base pairing.
  • Formation of initiation complex: The large subunit of the ribosome joins the small subunit, forming the complete ribosome and initiating the translation process.

Elongation

• Codon recognition: The ribosome moves along the mRNA, and each codon on the mRNA is recognized by a corresponding tRNA carrying the appropriate amino acid.
• Peptide bond formation: The ribosome facilitates the formation of a peptide bond between the amino acid carried by the tRNA in the P site and the amino acid carried by the tRNA in the A site.
• Translocation: The ribosome moves one codon down the mRNA, shifting the tRNA with the growing polypeptide chain to the P site and the now empty tRNA to the E site.

Termination

• Stop codon recognition: Translation continues until the ribosome encounters a stop codon (UAA, UAG, or UGA) on the mRNA.
• Release of polypeptide: Release factors bind to the ribosome at the stop codon, prompting the release of the completed polypeptide chain from the tRNA in the P site.
• Disassembly of ribosome: The ribosomal subunits, mRNA, and release factors dissociate, freeing the newly synthesized protein and allowing the ribosomal subunits to be reused for another round of translation.

Components

• mRNA: Carries the genetic code from DNA, specifying the sequence of amino acids in the protein.
• tRNA: Transfer RNA molecules bring the appropriate amino acids to the ribosome, each with an anticodon that pairs with a specific mRNA codon.
• Ribosome: The molecular machine that facilitates the synthesis of proteins, composed of rRNA and proteins, with three binding sites for tRNA: A site, P site, and E site.
• Aminoacyl-tRNA synthetase: Enzymes that attach the correct amino acid to its corresponding tRNA.
• Initiation, elongation, and release factors: Proteins that assist in the various stages of translation.

Codons

• Codons: A sequence of three nucleotides on the mRNA that corresponds to a specific amino acid or a stop signal.
• There are 64 possible codons.
• Redundancy: Multiple codons can code for the same amino acid, providing some tolerance for mutations.
• Start codon: AUG, which codes for methionine and signals the start of translation.
• Stop codons: UAA, UAG, and UGA, which signal the end of translation.