Fig. 16-1 Figure 16.1 How was the structure of DNA determined?

With your partner: Comparing/Contrasting nitrogen bases in DNA Similarities Differences

With scissors and glue, cut out and paste the DNA bases onto a piece of paper, showing how these base pairs could bond together.

Adenine (A) Thymine (T) Guanine (G) Cytosine (C) Fig. 16-8 Figure 16.8 Base pairing in DNA Guanine (G) Cytosine (C)

Discuss with your buddy: What is the valence number for the phosphorus atom in the phosphate group? How do you know? How do we count carbons in deoxyribose sugar? To which carbon in deoxyribose does the: nitrogen base attach? the next nucleotide? the phosphate?

Sugar–phosphate backbone 5 end Sugar (deoxyribose) 3 end Fig. 16-5 Sugar–phosphate backbone 5 end Nitrogenous bases Purines Adenine Guanine PurAsGold Pyrimidines Cytosine Thymine Uracil PyCUT Carbons in Deoxyribose sugar Carbon 1 – bonds to nitrogen base Carbon 3 – bonds to next nucleotide Carbon 5 – bonds to phosphate group Thymine (T) Adenine (A) Figure 16.5 The structure of a DNA strand Cytosine (C) Phosphate DNA nucleotide Sugar (deoxyribose) 3 end Guanine (G)

5 end Hydrogen bond 3 end 1 nm 3.4 nm 3 end 0.34 nm 5 end Fig. 16-7a 5 end Hydrogen bond 3 end 1 nm 3.4 nm Figure 16.7 The double helix 3 end 0.34 nm 5 end (a) Key features of DNA structure (b) Partial chemical structure