DNA structure and replication

Nature of science:

Making careful observations—Rosalind Franklin’s X-ray diffraction provided crucial evidence that DNA is a double helix. (1.8)

• 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.

• 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.

• 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.