7.1: DNA structure and replication
Teaching time: 3 hours Practical time: 0 hours
key vocabulary
prior learning & retrieval practice
Review 2.6 DNA Structure
Review 2.7 DNA replication, transcription & translation
DNA Structure
Essential idea: The structure of DNA is ideally suited to its function.
S1: Analysis of results of the Hershey and Chase experiment providing evidence that DNA is the genetic material.
Exercise 1: Using the video, outline the Hershey and Chase experiment.
Exercise 2: Outline how the experiment provided evidence that DNA is the genetic material
NoS: Making careful observations—Rosalind Franklin’s X-ray diffraction provided crucial evidence that DNA is a double helix. (1.8)
A1: Rosalind Franklin’s and Maurice Wilkins’ investigation of DNA structure by X-ray diffraction.
Exercise 3: Using the video, Outline Franklin and Wilkin's investigation of DNA.
U2: DNA structure suggested a mechanism for DNA replication.
Exercise 4: Read the relevant section of your textbook and connect-extend-challenge. Explain complementary base pairing in terms of purines and pyrimidines and the number of hydrogen bonds.
You can see the original paper here and Watson and Crick's reference to a possible mechanism within it.
How can we remember which bases are:
purines and which are pyrimidines?
single and double rings?
bond with two or three hydrogen bonds?
DNA structure original paper.pdf
U1: Nucleosomes help to supercoil the DNA.
Exercise 5: Describe the structure of a nucleosome and explain how it helps to supercoil DNA into a chromatin fibre.
S1: Utilization of molecular visualization software to analyse the association between protein and DNA within a nucleosome.
Exercise 6: Read the article about the nucleosome on the right and connect-extend-challenge. Then use the visualiser on the left to examine the nucleosome more cloesly.
DNA Replication
U3: DNA polymerases can only add nucleotides to the 3’ end of a primer.
U4: DNA replication is continuous on the leading strand and discontinuous on the lagging strand.
U5: DNA replication is carried out by a complex system of enzymes.
U6: Some regions of DNA do not code for proteins but have other important functions.
Guidance from the syllabus:
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.
Exercise 7: Explain DNA replication and create a table of enzymes and their functions.
DNA Sequencing
A2: Use of nucleotides containing dideoxyribonucleic acid to stop DNA replication in preparation of samples for base sequencing.
Exercise 8: Watch this video and connect-extend-challenge. Outline the how sequencing uses dideoxyrbonucleic acid to stop DNA sequencing.
A3: Tandem repeats are used in DNA profiling covered in topic 3.5
