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7.1 DNA structure and replication

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Description

Nature of science:
Making careful observations—Rosalind Franklin’s X-ray diffraction provided crucial evidence that DNA is a double helix. (1.8)
Understandings:
  • Nucleosomes help to supercoil the DNA.
  • DNA structure suggested a mechanism for DNA replication.
  • DNA polymerases can only add nucleotides to the 3’ end of a primer.
  • DNA replication is continuous on the leading strand and discontinuous on the lagging strand.
  • DNA replication is carried out by a complex system of enzymes.
  • Some regions of DNA do not code for proteins but have other important functions.
Applications and skills:
  • Application: Rosalind Franklin’s and Maurice Wilkins’ investigation of DNA structure by X-ray diffraction.
  • Application: Use of nucleotides containing dideoxyribonucleic acid to stop DNA replication in preparation of samples for base sequencing.
  • Application: Tandem repeats are used in DNA profiling.
  • Skill: Analysis of results of the Hershey and Chase experiment providing evidence that DNA is the genetic material.
  • Skill: Utilization of molecular visualization software to analyse the association between protein and DNA within a nucleosome.
 Theory of knowledge:
  • Highly repetitive sequences were once classified as “junk DNA” showing a degree of confidence that it had no role. To what extent do the labels and categories used in the pursuit of knowledge affect the knowledge we obtain?
Utilization:
Syllabus and cross-curricular links:
Biology
Topic 2.6 Structure of DNA and RNA

Aims:
  • Aim 6: Students could design models to illustrate the stages of DNA replication.
Guidance:
  • Details of DNA replication differ between prokaryotes and eukaryotes. Only the prokaryotic system is expected.
  • The proteins and enzymes involved in DNA replication should include helicase, DNA gyrase, single strand binding proteins, DNA primase and DNA polymerases I and III.
  • The regions of DNA that do not code for proteins should be limited to regulators of gene expression, introns, telomeres and genes for tRNAs.

 

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