WEB TUTORIAL 3.3
Nucleic Acids
Text Sections
Section 3.8 Nucleotides and Nucleic Acids, p. 50
Introduction
Nucleic acids such as DNA and RNA are polymers of nucleotides. DNA serves as
the primary storage of genetic information in nearly all organisms. In this tutorial,
you'll learn about the structure of nucleotides and how these monomers are joined
together to form nucleic acids such as DNA.
Learning Objectives
•
•
•
Describe the structure of a DNA nucleotide.
Know the four nitrogenous bases found in DNA molecules.
Understand how a double helix is formed from two DNA strands.
Narration
Nucleotides are important molecules in and of themselves and also serve as building blocks for a couple of very important molecules. A nucleotide is a molecule
with three parts: A phosphate group, a sugar (either ribose or deoxyribose), and a
nitrogen-containing base
As molecules in their own right, some nucleotides, called adenosine phosphates,
function as chemical energy carriers. For example, a molecule called adenosine
triphosphate, or ATP provides the energy necessary to get things done in living
organisms.
Nucleotides also serve as the building blocks of deoxyribonucleic acid, or DNA—
the primary information-bearing molecule of life. Four bases are found in DNA
molecules: Guanine (G), Cytosine (C), Adenine (A), and Thymine (T). The
nitrogenous bases in DNA bond together according to rather strict base pairing
rules: adenine bonds with thymine through two hydrogen bonds, and guanine
bonds with cytosine through three hydrogen bonds. The term complementary is
used to describe these pairings.
The sugar and phosphate components of the DNA molecule also link together to
form the outer “rails” of the DNA molecule. Each resulting nucleotide polymer is
called a nucleic acid. In DNA, the two nucleotide strands wind around one another to form a double helix.
You should now be able to…
•
•
•
•
List the three components of a nucleotide.
Explain the importance of ATP.
Specify the rules for complementary base pairing.
Discuss the orientation of the nucleotide components in a DNA molecule.