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The Structure of DNA
Photo credit: Jacob Halaska/Index Stock Imagery, Inc.
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2. The Components and Structure of DNA
What is the overall structure of the DNA molecule?
DNA is the abbreviation for deoxyribonucleic acid
It is a polymer made up of nucleotides (monomers).
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3. The Components and Structure of DNA
A nucleotide has 3 parts:
five-carbon sugar called deoxyribose
a phosphate group
a base made with nitrogen
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4. The Components and Structure of DNA
There are four kinds of bases in in DNA:
adenine
guanine
cytosine
thymine
DNA is made up of nucleotides. Each nucleotide has three parts: a deoxyribose molecule, a phosphate group, and a nitrogenous base. There are four different bases in DNA: adenine, guanine, cytosine, and thymine.
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5. The Components and Structure of DNA
The backbone of a DNA chain is formed by alternating sugar and phosphate groups of each nucleotide.
The bases connect in the center.
The nucleotides can be joined together in any order to make a long strand of DNA.
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6. The Components and Structure of DNA
How did we discover the structure of DNA? 
Rosalind Franklin used X-ray diffraction to get information about the structure of DNA.
The X-ray pattern gave clues that helped other scientists figure out the shape of the molecule.
This X-ray diffraction photograph of DNA was taken by Rosalind Franklin in the early 1950s. The X-shaped pattern in the center indicates that the structure of DNA is helical.
Photo credit: ©Cold Spring Harbor Laboratory Archives/Peter Arnold, Inc.
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7. The Components and Structure of DNA
The Double Helix 
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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What is the principle of base pairing?
Watson and Crick also discovered the two strands in the double helix are held together by hydrogen bonds.
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10. The Components and Structure of DNA
Watson and Crick discovered that these bonds can form only between certain base pairs
adenine and thymine (A & T)
guanine and cytosine (C & G)
(Way to remember = apple tree, chewing gum)
This principle is called base pairing.
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11. The Components and Structure of DNA
DNA Double Helix
DNA is a double helix in which two strands are wound around each other. Each strand is made up of a chain of nucleotides. The two strands are held together by hydrogen bonds between adenine and thymine and between guanine and cytosine.
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12. The Components and Structure of DNA
What are 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.
C = G; A = T
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