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IB DNA Structure Lab

DNA is the hereditary information found in humans, plants, protists, bacteria and all other living organisms.  Additionally, it is what makes each organisms on this planet unique.  The structure of DNA is referred to as a double helix because it is made of two strands of sugar and phosphates linked by nitrogen bases.  DNA is amazing in its ability to replicate and ensure that after mitosis each new cell contains an exact copies of the original DNA strand.  The structure of DNA was discovered 1953 by Watson and Crick, but multiple other scientists made discoveries that led to their findings[1]; Rosalind Franklin also had a significant contribution to our understanding of DNA today.



  1. Cut the two different colored long cord sweets into short lengths of approximately 2 cm. These will represent the deoxyribose sugar and phosphate; pick a different color to for each to use throughout your model building.  These represent the molecules that form the sides (backbone) of the DNA model.
  2. Use the needle and thread to string alternate lengths of the alternate colors of cord sweets together lengthwise.  Make two strands with 12 pieces each.
  3. Assign a different color of gum drops to each of the DNA base pairs: Adenine, Thymine, Cytosine, and Guanine. Write what base pairs the colors represent below.
  4. Thread two different color gum drops onto a toothpick; make sure that the sweets pair as DNA does.
  5. Place one toothpick stick with sweets between each alternate length of cord sweet to join the two sides.  
  6. Carefully hold each end of the cord sweets and twist slightly to represent the DNA double helix.
  7. Take a picture of your DNA double helix.
  8. Eat your delish DNA double helix, Happy Holidays!

Conclusion & Analysis:

  1. Identify which color gum drops were used for each nucleotide base
  1. Adenine:
  2. Guanine:
  3. Cytosine:
  4. Thymine:
  1. Draw a picture of a DNA double helix (both sides) with 3 base pairs (you can pick which bases to use).  Label each part of your drawing

  1. How are DNA nucleotides linked together and how are nitrogen bases held together?

  1. What is the difference between a purine and pyrimidine?  Give two examples of each.

  1. How does complementary base pairing and hydrogen bonds provide for the double helix structure of DNA?

[1] Pray, Leslie A. "Discovery of DNA Structure and Function: Watson and Crick." Nature Publishing Group, 2008. Web. 23 Oct. 2012.