1. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.1 Chapter 21 Nucleic Acids and Protein Synthesis 21.3DNA Double Helix

2. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. Percentage of Bases in DNA In Chargaff’s rules for DNA of various organisms,  the percentage of adenine (A) is the same as the percentage of thymine (T)  the percentage of guanine (G) is the same as the percentage of cytosine (C) 2

3. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. Complementary Base Pairs: A and T DNA contains complementary base pairs in which adenine is always linked by two hydrogen bonds to thymine (A−T).

4. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.4 Complementary Base Pairs: G and C DNA contains complementary base pairs in which  guanine is always linked by three hydrogen bonds to cytosine (G−C)

5. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.5 Double Helix of DNA The DNA structure is a double helix that  consists of two strands of nucleotides that form a double helix structure like a spiral stair case  has hydrogen bonds between the bases A–T and G–C  has bases along one strand that complement the bases along the other

6. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.6 Write the complementary base sequence for the matching strand in the following DNA section: Learning Check

7. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.7 Write the complementary base sequence for the matching strand in the following DNA section: Solution