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DNA Structure (2.6/7.1)

DNA Webquest: Tour of the basics

7.1 Nucleosome Activity:

 Visit the following website and check out some of the proteins 

-Click on the 3D images.  Look at the different folding patterns.

2.6 Structure of DNA and RNA

Nature of science:

Using models as representation of the real world—Crick and Watson used model making to discover the structure of DNA. (1.10)


The nucleic acids DNA and RNA are polymers of nucleotides.

DNA differs from RNA in the number of strands present, the base composition and the type of pentose.

DNA is a double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs.

Applications and skills:

Application: Crick and Watson’s elucidation of the structure of DNA using model making.

Skill: Drawing simple diagrams of the structure of single nucleotides of DNA and RNA, using circles, pentagons and rectangles to represent phosphates, pentoses and bases.


In diagrams of DNA structure, the helical shape does not need to be shown, but the two strands should be shown antiparallel. Adenine should be shown paired with thymine and guanine with cytosine, but the relative lengths of the purine and pyrimidine bases do not need to be recalled, nor the numbers of hydrogen bonds between the base pairs.

Theory of knowledge:

The story of the elucidation of the structure of DNA illustrates that cooperation and collaboration among scientists exists alongside competition between research groups. To what extent is research in secret ‘anti-scientific’? What is the relationship between shared and personal knowledge in the natural sciences?

Essential Idea: Genetic information in DNA can be accurately copied and can be translated to make the proteins needed by the cell.

7.1 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.

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?


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.

Essential idea: Information stored as a code in DNA is copied onto mRNA.