6 DNA Structure and Replication

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					                                 C H A P T E R
                                DNA Structure
                                and Replication
 How are traits stored
 in chromosomes?
 Why is DNA called the       When a pianist sits down at the           chemicals in the cells of all
 “code of life”?             piano, he or she can strike the           organisms can be combined to form
 How do cells copy genetic   88 piano keys in millions of different    molecules of DNA. Although the
 information?                combinations to make music. The           DNA molecule can hold an enormous
                             number of combinations in which the       amount of genetic information, it is
                             keys can be played together is as         based on a simple code. You will
                             endless as the number of composers        learn how to read this code and then
                             who have written, or will write,          model your own DNA molecules. You
                             music. The difference between music       will also learn how the DNA
                             and noise, however, depends on            molecule is used as a template to
                             striking the keys in a particular         form new molecules of DNA. Finally,
                             sequence. Every keyboard is the           you will explore recent genetic
                             same; the difference from one song to     technologies, such as DNA
                             the next is how the notes are arranged.   fingerprinting and cloning, and learn
                                All organisms are formed from the      how they are used to identify
                             same chemicals, and yet they all look     individuals.
                             so different. The key is how the
                             chemicals in their cells are arranged.
                             Just as different combinations of
                             piano keys make different tunes, the
                             chemicals in cells can be arranged in          How is genetic information
                             a variety of ways to produce the               organized in DNA?
                             many thousands of characteristics.
                             For example, people share many
                             characteristics. They have a similar
                             body shape and structure. This is
                             because they are made of the same
                             chemical compounds. However, there
                             is considerable variation from person
                             to person. People vary in height, eye
                             colour, hair colour, and other traits.
                             This variation occurs because the
                             chemical compounds can be arranged
                             in different combinations. The
                             organization of these chemical
                             compounds forms the basis for
                             genetic variation.
                                In this chapter, you will find out
                             what kinds of scientific research led
                             to the discovery of the DNA
                             molecule. You will learn how


 6.1 The Structure of DNA    186   Investigation 6-A: DNA            6.2 DNA Replication      199
                                   Extraction                  192
 Thinking Lab: Evidence                                              MiniLab: Modelling DNA
 for Nucleotide Pairs        190   MiniLab: Reading the Code   195   Replication              200
 MiniLab: Nucleotide Model   191   Thinking Lab: Reading a           Thinking Lab: Genetic
                                   DNA Fingerprint             197   Technologies             203


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