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Series: Biology: DNA Structure Revealed


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About this Series

  • Lessons: 2
  • Total Time: 0h 22m
  • Use: Watch Online & Download
  • Access Period: Unlimited
  • Created At: 06/23/2009
  • Last Updated At: 11/03/2009

This two part series covers DNA's history and structure. Professor Wolfe explains the history behind the discovery of the strucutre of DNA. Molecules are too small to observe, and this means it was impossible to determine the molecular structure of DNA. In 1950, Franklin and Wilkins used X-ray defraction to create images of DNA, exposing a possible helical structure. They also determined 3 repetitive ratios, 0.34, 3.4, and 2.0, but did not know what these represented. This information was used by Watson and Crick to develop the first accurate approximation of the structure of DNA. They began with the belief that the structure was a double-helix and used molecular models, to piece together the structure. Watson and Crick discovered that the 0.34 nm number was the distance between each nucleotide, and the 3.4 nm number was 10 nucleotides. The 2.0 nm number they determined to be the diameter of the helix. They also discovered that purines and pyrimidines created a hydrogen bond across the double-helix. Using these dimensions and information, they created the model of DNA that has become the foundation for molecular genetics.

In 1953, Watson and Crick published their findings on the structure of DNA in the journal Nature. Knowing the structure of DNA allows us to understand how it works in the body. Professor Wolfe further explains their findings and how measurements from the X-ray defraction image helped define the structure of the DNA. These are the 0.34, 3.4, and 2.0 measurements that were observed in the image, but not understood. He also explains the bonding between the purines and pyrimidines. These are hydrogen bonds, formed in the middle of the double-helix. The sugar-phosphate chains are antiparallel. Finally, Professor Wolfe explains the four requirements of DNA, that it is informational, capable of replication, capable of communicating with cells, and capable of change, and how DNA meets all of these requirements.

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

About this Author

2174 lessons

Founded in 1997, Thinkwell has succeeded in creating "next-generation" textbooks that help students learn and teachers teach. Capitalizing on the power of new technology, Thinkwell products prepare students more effectively for their coursework than any printed textbook can. Thinkwell has assembled a group of talented industry professionals who have shaped the company into the leading provider of technology-based textbooks. For more information about Thinkwell, please visit or visit Thinkwell's Video Lesson Store at

Thinkwell lessons feature a star-studded cast of outstanding university professors: Edward Burger (Pre-Algebra through...

Lessons Included

Rosalind Franklin
~ ycamacho

You seem to have forgotten that Rosalind Franklin played a huge role in the discovery of DNA!!! Why was she not mentioned?

Below are the descriptions for each of the lessons included in the series:

Supplementary Files: