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. 1

Chapter 21 Nucleic Acids and Protein Synthesis

21.3 DNA 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)

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General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Complementary Base Pairs: A and TDNA contains complementary base pairs in which adenine is always linked by two hydrogen bonds to thymine (A−T).

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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)

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Double Helix of DNA

The DNA structure is adouble 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

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Write the complementary base sequence for the matching strand in the following DNA section:

Learning Check

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Write the complementary base sequence for the matching strand in the following DNA section:

Solution