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Biology
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12–1 DNA
Photo credit: Jacob Halaska/Index Stock Imagery, Inc.
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3. Griffith and Transformation
In 1928, British scientist Fredrick Griffith was trying to learn how certain types of bacteria caused pneumonia.
He isolated two different strains of pneumonia bacteria from mice and grew them in his lab.
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4. The Hershey-Chase Experiment
Alfred Hershey and Martha Chase studied viruses—nonliving particles smaller than a cell that can infect living organisms.
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5. The Hershey-Chase Experiment
Bacteriophages 
A virus that infects bacteria is known as a bacteriophage.
Bacteriophages are composed of a DNA or RNA core and a protein coat.
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6. The Hershey-Chase Experiment
When a bacteriophage enters a bacterium, the virus attaches to the surface of the cell and injects its genetic information into it.
The viral genes produce many new bacteriophages, which eventually destroy the bacterium.
When the cell splits open, hundreds of new viruses burst out.
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7. The Hershey-Chase Experiment
Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein.
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8. What is the overall structure of the DNA molecule?
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9. The Components and Structure of DNA
DNA is made up of nucleotides.
A nucleotide is a monomer of nucleic acids made up of 3 parts
five-carbon sugar called deoxyribose
a phosphate group
and a nitrogenous base.
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10. 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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11. 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. 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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13. The Components and Structure of DNA
X-Ray Evidence 
Rosalind Franklin used X-ray diffraction to get information about the structure of DNA.
She aimed an X-ray beam at concentrated DNA samples and recorded the scattering pattern of the X-rays on film.
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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14. The Components and Structure of DNA
The Double Helix 
Using clues from Franklin’s pattern, 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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15. 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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16. 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.
Quiz Tomorrow! Study!
HW: WB #17-28
Due Tomorrow!
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12–1
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12–1
Avery and other scientists discovered that
DNA is found in a protein coat.
DNA stores and transmits genetic information from one generation to the next.
transformation does not affect bacteria.
proteins transmit genetic information from one generation to the next.
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12–1
The Hershey-Chase experiment was based on the fact that
DNA has both sulfur and phosphorus in its structure.
protein has both sulfur and phosphorus in its structure.
both DNA and protein have no phosphorus or sulfur in their structure.
DNA has only phosphorus, while protein has only sulfur in its structure.
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12–1
DNA is a long molecule made of monomers called
nucleotides.
purines.
pyrimidines.
sugars.
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12–1
Chargaff's rules state that the number of guanine nucleotides must equal the number of
cytosine nucleotides.
adenine nucleotides.
thymine nucleotides.
thymine plus adenine nucleotides.
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12–1
In DNA, the following base pairs occur:
A with C, and G with T.
A with T, and C with G.
A with G, and C with T.
A with T, and C with T.
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