12.2_The_Structure_of_DNA
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Transcript 12.2_The_Structure_of_DNA
1 Review List the chemical components of DNA
Relate Cause and Effect Why are hydrogen bonds so
essential to the structure of DNA
2 Review Describe the discoveries that led to the
modeling of DNA
Infer Why did scientists have to use tools other than
microscopes to solve the structure of DNA
3 Review Describe Watson and Crick’s model of the
DNA model
CH 12 DNA
12.2 The Structure of DNA
Nucleic Acids and Nucleotides
DNA nucleotides are made up of
Deoxyribose
Phosphate
Nitrogen
base
DNA has four kinds of nitrogenous bases
Adenine (A)
Thymine (T)
Guanine
(G)
Cytosine (C).
Nucleic acids are a chain of nucleotides
Nucleotides can be joined in any order.
Solving the Structure of DNA
Chargaff’s Rules
Percentages of adenine [A] and thymine [T] bases
are almost equal in any sample of DNA
Same with guanine [G]
and cytosine [C]
A=T
C=G.
Franklin’s X-Rays
X-ray diffraction
X-shaped pattern showing
that the strands in DNA are
twisted
Angle of the X-shaped
pattern suggested two
strands
Width of X suggested width.
Watson and Crick
Used clues from
Franklin’s X-ray
Used Chargaff’s rules
Proposed structure for
double helix.
The Double-Helix Model
Antiparallel Strands
Hydrogen Bonding
Base Pairing.
Antiparallel Strands
Two strands of DNA run in opposite directions
A-T-C-G-C-G-A-T
T-A-G-C-G-C-T-A
Hydrogen Bonding
Relatively weak chemical
bonds
Allows for two strands to
separate.
Base Pairing
A binds with T
C binds with G.
1.
2.
3.
Interpret Tables Which organism has the highest
percentage of adenine
Calculate If a species has 35% adenine in its DNA
what is the percentage of the other three bases
What did the fact that A and T, and C and G,
occurred in equal amounts suggest about the
relationship among these bases