Source :

http://www.accessexcellence.org/RC/AB/WYW/wkbooks/SFTS/activity1.php

8 : 55 p.m. 27/11/2011

1. What nucleotides can form a stable hydrogen bond with the adenine nucleotide? (Adenine and thymine.) With the cytosine nucleotide? (Cytosine

and

guanine.) 

2. How can the nucleotide pairs be arranged so the width of the pairs is always the same? (Adenine with the keto form of thymine and cytosine with the keto form of guanine.) Is this important? (Yes.) Why or why not? (It allows the width between phosphate strands to remain consistent.)

3. Edwin Chargaff found that within human DNA the amounts of adenine and thymine were approximately equal and the amounts of guanine and cytosine were also approximately equal. If adenine paired with guanine, would Chargaff's findings hold? (Maybe.) What if adenine paired with thymine? (Yes.) If adenine paired with cytosine? (Maybe.)

Extension

Cytosine and adenine also form tautomers called imino and amino forms. Have students research the structure of these forms. Ask students to try to create models of base pairs using the alternate forms.