6- Translation

• Genome


  All the genes in a cell
• Messenger RNA (mRNA)


  The RNA copy of the base sequence of a gene that moves to the cytoplasm
• Genetic code


  The series of triplets (codons) in mRNA that determine the amino acid sequence of a polypeptide
• Features of the genetic code

  • Degenerate (more than one triplet for most amino acids)
  • Non-overlapping (no base is read more than once)
  • Universal (same triplets encode the same amino acids in most organisms)
• Start codon


  The triplet that determines where to start translating the mRNA molecule
• Stop codons


  The three triplets that determine where translation stops
• Transfer RNA (tRNA)


  The RNA molecule that carries amino acids to the ribosome during translation
• Translation


  1. mRNA binds to small ribosome subunit

  2. tRNA with anticodon complementary to start codon attaches

  3. Second tRNA with anticodon complementary to next codon attaches

  4. Peptide bond forms between amino acids

  5. Ribosome moves to next codon

  6. First tRNA released

  7. Process continues until stop codon reached
• Ribosomes contain proteins and ribosomal RNA
• Peptide bond formation is catalyzed by the enzyme peptidyl transferase, which is part of the ribosomal RNA
• Energy from ATP is required for peptide bond formation
• Multiple ribosomes can attach to an mRNA and translate it simultaneously, allowing rapid production of multiple polypeptide molecules
• Once a polypeptide is correctly folded, it can carry out its function in the cell