Labeled diagram of DNA structure illustrating nucleotides, sugar, phosphate, and complementary base pairing.

9. Chargaff's rule states that the DNA of any species contains equal amounts of adenine and thymine and also equal amounts of guanine and cytosine.

10. Based on this information, scientist could predict that the base adenine pairs with thymine and the base guanine pairs with cytosine in the formation of the DNA molecule. This is called complementary base pairs. Thus one strand of DNA is complementary to the other strand (opposite/matching).

11. The bases are paired by hydrogen bonds along the axis of the molecule.

12. Wilkins and Franklin studied the structure of DNA using X-ray crystallography, a technique to examine molecules, and helped Watson and Crick determined that the shape of the molecule was a double helix.

13. Draw the basic structure of a nucleotide with its three parts.
- A phosphate group (circle or sphere)
- A five-carbon sugar (deoxyribose, pentagon shape)
- A nitrogenous base (rectangle or hexagon attached to sugar)

14. Write the complementary sequence to following DNA strand:
A A T T C G C C G G T A T T A G A C G T T
T T A A G C G G C C A T A A T C T G C A A

15. Use the image at the right to complete the follow:
Circle a nucleotide: (Circle one complete unit: phosphate + sugar + base)
Label the sugar and phosphate: (Label the pentagon as "sugar" and the circle/sphere as "phosphate")
Label the bases that are not already labeled: (Label the unlabeled rectangles as "T", "G", "C", "A" according to complementarity: opposite A is T, opposite T is A, opposite G is C, opposite C is G)