2.7  DNA Replication, Transcription & Translation

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Essential Idea:

Genetic information in DNA can be accurately copied and

can be translated to make the proteins needed by the cell


  • The replication of DNA is semi-conservative and depends on complementary base pairing
  • Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds
  • DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template
  • Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase
  • Translation is the synthesis of polypeptides on ribosomes
  • The amino acid sequence of polypeptides is determined by mRNA according to the genetic code
  • Codons of three bases on mRNA correspond to one amino acid in a polypeptide
  • Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA


  • Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR)
  • Production of human insulin in bacteria as an example of the universality of the genetic code allowing for gene transfer between species


  • Use a table of the genetic code to deduce which codon(s) correspond to which amino acid
  • Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA
  • Use a table of mRNA codons and their corresponding amino acids to deduce the sequence of amino acids coded by a short mRNA strand of known base sequence
  • Deducing the DNA base sequence for the mRNA strand