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