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Nucleic Acids
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
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Printed: November 6, 2015
AUTHORS
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
www.ck12.org
C HAPTER
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Chapter 1. Nucleic Acids
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Nucleic Acids
Describe the composition of a nucleic acid.
List the components of a nucleotide.
Identify significant differences between DNA and RNA.
Describe the shape of DNA.
Summarize significant roles of nucleic acids.
You may have heard that something is "encoded in your DNA." What does that mean?
Nucleic acids. Essentially the "instructions" or "blueprints" of life. Deoxyribonucleic acid, or DNA, is the unique
blueprints to make the proteins that give you your traits. Half of these blueprints come from your mother, and half
from your father. Therefore, every person that has ever lived - except for identical twins - has his or her own unique
set of blueprints - or instructions - or DNA.
Nucleic Acids
A nucleic acid is an organic compound, such as DNA or RNA, that is built of small units called nucleotides. Many
nucleotides bind together to form a chain called a polynucleotide. The nucleic acid DNA (deoxyribonucleic acid)
consists of two polynucleotide chains. The nucleic acid RNA (ribonucleic acid) consists of just one polynucleotide
chain.
An overview of DNA can be seen at http://www.youtube.com/watch?v=_-vZ_g7K6P0 (28:05).
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/199
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As you view DNA, focus on the following concept:
1. the structure and role of DNA.
Structure of Nucleic Acids
Each nucleotide consists of three smaller molecules:
1. sugar
2. phosphate group
3. nitrogen base
If you look at Figure 1.1, you will see that the sugar of one nucleotide binds to the phosphate group of the next
nucleotide. These two molecules alternate to form the backbone of the nucleotide chain. This backbone is known as
the sugar-phosphate backbone.
The nitrogen bases in a nucleic acid stick out from the backbone. There are four different types of bases: cytosine
(C), adenine (A), guanine (G), and either thymine (T) in DNA, or uracil (U) in RNA. In DNA, bonds form between
bases on the two nucleotide chains and hold the chains together. Each type of base binds with just one other type of
base: cytosine always binds with guanine, and adenine always binds with thymine. These pairs of bases are called
complementary base pairs.
FIGURE 1.1
Nucleic Acid.
Sugars and phosphate
groups form the backbone of a polynucleotide chain. Hydrogen bonds between
complementary bases hold two polynucleotide chains together.
The binding of complementary bases allows DNA molecules to take their well-known shape, called a double helix,
which is shown in Figure 1.2. A double helix is like a spiral staircase. The double helix shape forms naturally and
is very strong, making the two polynucleotide chains difficult to break apart.
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Chapter 1. Nucleic Acids
FIGURE 1.2
DNA Molecule. Bonds between complementary bases help form the double helix
of a DNA molecule.
The letters A, T,
G, and C stand for the bases adenine,
thymine, guanine, and cytosine. The sequence of these four bases in DNA is a
code that carries instructions for making
proteins. Shown is how the DNA winds
into a chromosome.
An animation of DNA structure can be viewed at http://www.youtube.com/watch?v=qy8dk5iS1f0 .
Roles of Nucleic Acids
DNA is also known as the hereditary material or genetic information. It is found in genes, and its sequence of bases
makes up a code. Between "starts" and "stops," the code carries instructions for the correct sequence of amino acids
in a protein (see Figure 1.3). DNA and RNA have different functions relating to the genetic code and proteins. Like
a set of blueprints, DNA contains the genetic instructions for the correct sequence of amino acids in proteins. RNA
uses the information in DNA to assemble the correct amino acids and help make the protein. The information in
DNA is passed from parent cells to daughter cells whenever cells divide. The information in DNA is also passed
from parents to offspring when organisms reproduce. This is how inherited characteristics are passed from one
generation to the next.
Summary
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DNA and RNA are nucleic acids. Nucleic acids are built of small units called nucleotides.
The bases of DNA are adenine, guanine, cytosine and thymine. In RNA, thymine is replaced by uracil.
In DNA, A always binds to T, and G always binds to C.
The shape of the DNA molecule is known as a double helix.
DNA contains the genetic instructions for the correct sequence of amino acids in proteins. RNA uses the
information in DNA to assemble the correct amino acids and help make the protein.
Explore More
Use this resource to answer the questions that follow.
• What is DNA? at http://learn.genetics.utah.edu/content/begin/dna/ .
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FIGURE 1.3
The letters G, U, C, and A stand for the bases in RNA. Each group of three bases makes up a code word, and
each code word represents one amino acid (represented here by a single letter, such as V, H, or L). A string of
code words specifies the sequence of amino acids in a protein.
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2.
3.
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Why is DNA referred to as the "instructions"?
Where is DNA located in the cell?
What do A, C, G and T refer to? How can only four letters tell the cell what to do?
What is a gene?
Review
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Identify the three parts of a nucleotide.
What is DNA?
What are complementary base pairs? Give an example.
Describe the shape of DNA.
How are DNA and RNA related to proteins?
References
1. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation. Structure of a nucleic acid . CC BY-NC 3.0
2. Marianna Ruiz Villarreal (LadyofHats) for the CK-12 Foundation. How DNA folds into chromosomes . CC
BY-NC 3.0
3. Madeleine Price Ball, modified by CK-12 Foundation. RNA codon and protein sequence . Public Domain
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