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12–1 DNA STRUCTURE
12–1 DNA
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The Components and Structure of DNA
What is the overall structure of the DNA molecule?
12–1 DNA
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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
1.Five-carbon sugar called deoxyribose
2.Phosphate group
3.Nitrogenous base.
12–1 DNA
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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 (the sides of the ladder) is formed by sugar and phosphate groups of each nucleotide.
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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.
12–1 DNA
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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.
12–1 DNA
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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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The Components and Structure of DNA
DNA Double Helix
12–1 DNA
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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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Avery and other scientists discovered that
a. DNA is found in a protein coat.
b. DNA stores and transmits genetic information from one generation to the next.
c. transformation does not affect bacteria.
d. proteins transmit genetic information from one generation to the next.
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The Hershey-Chase experiment was based on the fact that
a. DNA has both sulfur and phosphorus in its structure.
b. protein has both sulfur and phosphorus in its structure.
c. both DNA and protein have no phosphorus or sulfur in their structure.
d. DNA has only phosphorus, while protein has only sulfur in its structure.
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DNA is a long molecule made of monomers called
a. nucleotides.
b. purines.
c. pyrimidines.
d. sugars.
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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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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.
END OF SECTION