WEB TUTORIAL 13.1
The Structure of DNA
Text Sections
Section 13.3 The Components of DNA and Arrangement, p. 206
Introduction
A single DNA strand is a polymer of nucleotides. Each nucleotide is composed of
a sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine). Thousands of these four nucleotides are bonded
together in a linear strand. Two DNA strands then hydrogen bond and twist together to form the double helix. During the process of semiconservative replication, the
DNA strands separate and serve as templates so that new DNA strands can be created by the enzyme DNA polymerase.
Learning Objectives
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Know the components that make up a DNA nucleotide.
Understand how DNA is replicated.
Discuss how a DNA double helix is formed.
Narration
The Structure of DNA
The building blocks of DNA are units called nucleotides. Nucleotides are composed of three types of component molecules: phosphate groups, the sugar
deoxyribose, and a nitrogenous base. There are four common bases: adenine (A),
guanine (G), thymine (T), and cytosine (C).
The DNA molecule consists of two separate chains of nucleotides, usually called
strands. Within each strand, the phosphate group of one nucleotide bonds to the
sugar of the next nucleotide in the strand. This bonding pattern produces a “backbone” of alternating, covalently bonded sugars and phosphates.
Each base extends from one backbone to the other to link up, via hydrogen bonds,
with a complementary base from the other side. Base pairing is complementary,
i.e., A always pairs with T, and G always pairs with C.
The two nucleotide strands in a DNA molecule are wound around one another to
form a double helix.
You should now be able to…
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List the 4 nitrogenous bases found in DNA.
Build a strand of DNA using the rules of complementary base pairing.
Explain where each component of a nucleotide is located in the DNA double helix.
Describe the semiconservative model of DNA replication.