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2.7 DNA replication, transcription and translation

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Description

Nature of science:
Obtaining evidence for scientific theories—Meselson and Stahl obtained evidence for the semi-conservative replication of DNA. (1.8)
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.
Guidance:
  • The different types of DNA polymerase do not need to be distinguished.
 Utilization:
Syllabus and cross-curricular links:
Biology
Topic 3.5 Genetic modification and biotechnology
Topic 7.2 Transcription and gene expression
Topic 7.3 Translation

Aims:
  • Aim 8: There are ethical implications in altering the genome of an organism in order to produce proteins for medical use in humans.

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