DNA Structures


  1. Describe the structure of DNA. Identify the following: Base, nucleotide, 5’end, 3’end, phosphate, deoxyribose, ribose, major groove, minor groove, double helix.
  2. Compare and contrast the chemical structures of DNA and RNA.
  3. Predict the sequence of one strand of DNA given the sequence of the complementary strand.
  4. Recognize the difference between DNA, chromatin, chromatid, chromosome, and genome.
  5. Describe how proteins are used to compact eukaryotic chromosomes.

Source material

Nucleic Acids and DNA Double Helical Structure modified from Openstax Biology, 2e, by Mary Ann Clark, Matthew Douglas, and Jung Choi. Selections from Chapter 3.5 (Nucleic Acids) and Chapter 14.2 (DNA Structure and Sequencing). Access for free at OpenStax.

Chromatin compaction modified from Online Open Genetics (Nickle and Barrette-Ng), available through Biology LibreTexts.


Genetics is the study of the inheritance of traits from parent to offspring, from generation to generation. Humans have long been aware that the characteristics of an individual plant or animal in a population could be passed down through the generations: Offspring tend to look more like their biological parents than unrelated adults. Humans also knew that some characteristics (such as the size or color of fruit) varied between individuals and that agricultural crops and domestic animals could be bred for the most favorable traits. Knowledge of these hereditary properties has been of significant value in the history of human development. However, human understanding of how these traits are inherited is a relatively new science.

It all comes down to DNA: the genetic material.

A common saying in biology is “structure dictates function”, or, sometimes, “form follows function”. In everyday terms, this means that the structure of an object – be it a part of an organism, part of a cell, or a molecule – determines what that object can be used for. To use an analogy: a wheel must be round to roll.

Until the mid-1950s, it was very difficult for scientists to imagine how a chemically simple molecule like DNA could possibly store enough information to build a biologically complex organism like a human. And it was even more difficult to understand how that information could be shared from generation to generation. The structure of DNA, however, once understood, immediately suggested how genetic information could be transmitted. The structure of the molecule made it possible.

The story of DNA structure also illustrates how modern science works, with each generation of researchers building on the work of previous generations and their own contemporaries: Each new insight is dependent on what has come before. Although James Watson and Francis Crick are the most well-known names in the history of DNA structure, their insights were dependent on the work of many other researchers as well.

In this module, we will look at the chemical structure of DNA as well as a few key experiments in the decades of work that led up to the determination of DNA structure.


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