Biology
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Chapter 12 DNA
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12–1 DNA
Avery and DNA
What did scientists discover about the
relationship between genes and DNA?
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12–1 DNA
Avery and DNA
Scientists discovered that the nucleic
acid DNA stores and transmits the
genetic information from one generation
of an organism to the next.
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12–1 DNA
The Components and Structure of DNA
What is the overall structure of the DNA
molecule?
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12–1 DNA
The Components and Structure of DNA
The Components and Structure of DNA
DNA is made up of nucleotides.
A nucleotide is a monomer of nucleic acids made
up of a five-carbon sugar called deoxyribose, a
phosphate group, and a nitrogenous base.
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The Components and Structure of DNA
There are four
kinds of bases in
in DNA:
• adenine
• guanine
• cytosine
• thymine
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The Components and Structure of DNA
The backbone of a DNA chain is formed by sugar
and phosphate groups of each nucleotide.
The nucleotides can be joined together in any order.
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12–1 DNA
The Components and Structure of DNA
Chargaff's Rules
Erwin Chargaff discovered that:
• The percentages of guanine [G] and cytosine
[C] bases are almost equal in any sample of
DNA.
• The percentages of adenine [A] and thymine
[T] bases are almost equal in any sample of
DNA.
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12–1 DNA
The Components and Structure of DNA
The Double Helix
Using clues from other scientists, James
Watson and Francis Crick built a model that
explained how DNA carried information and
could be copied.
Watson and Crick's model of DNA was a
double helix, in which two strands were
wound around each other.
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The Components and Structure of
DNA
DNA Double Helix
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The Components and Structure of
DNA
Watson and Crick discovered that hydrogen bonds
can form only between certain base pairs—adenine
and thymine, and guanine and cytosine.
This principle is called base pairing.
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12–1
DNA is a long molecule made of monomers
called
a. nucleotides.
b. purines.
c. pyrimidines.
d. sugars.
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12–1
Chargaff's rules state that the number of
guanine nucleotides must equal the number of
a. cytosine nucleotides.
b. adenine nucleotides.
c. thymine nucleotides.
d. thymine plus adenine nucleotides.
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12–1
In DNA, the following base pairs occur:
a. A with C, and G with T.
b. A with T, and C with G.
c. A with G, and C with T.
d. A with T, and C with T.
Go to Section 12-2
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