1 review list the chemical components of dna relate cause and effect why are hydrogen bonds so...
TRANSCRIPT
1 Review List the chemical components of DNA Relate Cause and Effect Why are hydrogen bonds so
essential to the structure of DNA2 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 DNA3 Review Describe Watson and Crick’s model of the
DNA model
CH 12 DNA12.2 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. Interpret Tables Which organism has the highest percentage of adenine
2. Calculate If a species has 35% adenine in its DNA what is the percentage of the other three bases
3. What did the fact that A and T, and C and G, occurred in equal amounts suggest about the relationship among these bases