2.7 DNA replication, transcription and translation

Understandings:

• • 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.

• • Applications and skills:

    • Application: Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR).

    • Application: Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species.

    • Skill: Use a table of the genetic code to deduce which codon(s) corresponds to which amino acid.

      • • • Skill: Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA.

          • Skill: 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.

          • Skill: Deducing the DNA base sequence for the mRNA strand.