Essential idea: The structure of DNA is ideally suited to its function.
From reactive bases that bond easily with their complements to the nucleoside tri-phosphates that can with them the energy to bond and build a strand of DNA. The structure of DNA is ideally suited to replicating itself and storing information.
Understandings, applications and skills
| 7.1.U1 | Nucleosomes help to supercoil the DNA. |
| 7.1.U2 | DNA structure suggested a mechanism for DNA replication. |
| 7.1.U3 | DNA polymerases can only add nucleotides to the 3’ end of a primer. |
| 7.1.U4 | DNA replication is continuous on the leading strand and discontinuous on the lagging strand. [Details of DNA replication differ between prokaryotes and eukaryotes. Only the prokaryotic system is expected.] |
| 7.1.U5 | DNA replication is carried out by a complex system of enzymes. [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.] |
| 7.1.U6 | Some regions of DNA do not code for proteins but have other important functions. [The regions of DNA that do not code for proteins should be limited to regulators of gene expression, introns, telomeres and genes for tRNAs.] |
| 7.1.A1 | Rosalind Franklin’s and Maurice Wilkins’ investigation of DNA structure by X-ray diffraction. |
| 7.1.A2 | Use of nucleotides containing dideoxyribonucleic acid to stop DNA replication in preparation of samples for base sequencing. |
| 7.1.A3 | Tandem repeats are used in DNA profiling. |
| 7.1.S1 | Analysis of results of the Hershey and Chase experiment providing evidence that DNA is the genetic material. |
| 7.1.S2 | Utilization of molecular visualization software to analyse the association between protein and DNA within a nucleosome. |
[Text in square brackets indicates guidance notes]
Starter
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Drew Berry talks at TEDxCaltech about his visualization of Biology with a particular focus on DNA. These examples show how the unseeable molecules can be visualised and hence better understood.
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A fast paced introduction (and refresher of core content) from Hank Green
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Presentation and notes
The presentation is designed to help your understanding. The notes outline is intended to be used as a framework for the development of student notes to aid revision.
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Weblinks
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DNA Structure
DNA by Khan Academy DNA Anatomy by John Kyrk Build a DNA Molecule by learn.genetics DNA Replication DNA Replication by St Olaf College DNA Replication by Wiley DNA Replication visualisation style animation by HHMI DNA Double Helix Game by Nobelprize.org DNA Replication (a detailed animation) by John Kyrk DNA Packaging DNA Molecule: how DNA is packaged by the DNA Learning Center Nucleosomes The 3D packaging of nuclear chromosomes by W H Freeman Chromatin remodelling by McGraw and Hill DNA packaging visualisation by HHMI |
Hershey and Chase Experiment
Hershey and Chase Experiment by McGraw and Hill The Hershey-Chase Experiment by Access Excellence The Hershey and Chase Experiments by John Kimball X-Ray diffraction of DNA Franklin's X-Ray diffraction by the DNA Learning Center Base sequencing How to sequence the human genome - Mark J. Kiel |
Nature of science
Making careful observations—Rosalind Franklin’s X-ray diffraction provided crucial evidence that DNA is a double helix. (1.8)
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?
The amount of noncoding (aka junk) DNA in different organisms varies hugely. Over 98% of the human genome is noncoding DNA, while only about 2% of a typical bacterial genome is noncoding DNA. With such variance and such a high proportion of DNA being noncoding the noncoding DNA was never truly ignored. In early DNA research the focus was very much on coding DNA as it's effect was more easily measured by the polypeptides and proteins generated by expression. noncoding DNA is now a controversial area of research and one with no definite answer.
Though we know that noncoding DNA has roles to play particularly in relation to transcription regulation we definitely don't know the whole story. Onions for example have a genome five times larger than humans with far more noncoding DNA than our known. This raises two obvious and unanswered questions: Do onions need all that noncoding DNA? If so what role does it play?
One thing we know for sure - we have a lot still to learn about DNA, how DNA carries information and more crucially how DNA is expressed.
Read the articles below to find out more:
The amount of noncoding (aka junk) DNA in different organisms varies hugely. Over 98% of the human genome is noncoding DNA, while only about 2% of a typical bacterial genome is noncoding DNA. With such variance and such a high proportion of DNA being noncoding the noncoding DNA was never truly ignored. In early DNA research the focus was very much on coding DNA as it's effect was more easily measured by the polypeptides and proteins generated by expression. noncoding DNA is now a controversial area of research and one with no definite answer.
Though we know that noncoding DNA has roles to play particularly in relation to transcription regulation we definitely don't know the whole story. Onions for example have a genome five times larger than humans with far more noncoding DNA than our known. This raises two obvious and unanswered questions: Do onions need all that noncoding DNA? If so what role does it play?
One thing we know for sure - we have a lot still to learn about DNA, how DNA carries information and more crucially how DNA is expressed.
Read the articles below to find out more:
