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

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

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

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

7. 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?

8. Sugar–phosphate backbone 5 end Sugar (deoxyribose) 3 end
Fig. 16-5
Sugar–phosphate backbone  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)  end
Guanine (G)

9. 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