Chapter 12.2 (Pg. 344-348):
The Structure of DNA
Deoxyribonucleic Acid (DNA)
- A nucleic acid made up of
nucleotides joined into long
chains by covalent bonds
- Nucleotides have 3 parts:
- Deoxyribose (5-carbon sugar)
- Phosphate group
- Nitrogenous base
Nitrogenous Bases
- Bases that contain nitrogen
- Four Types:
-
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
- Covalent bonds join nucleotides
together in many different orders
- Makes DNA backbone
Solving the Structure of DNA
- Erwin Chargaff:
- % of Adenine = % of Thymine
- % of Guanine = % of Cytosine
- Chargaff’s Rule: [A]=[T]; [G]=[C]
- Rosalind Franklin
- Shot X-Ray beams at DNA samples
- Hypothesized a spiral structure
- Watson and Crick
- Used Franklin’s x-ray pictures to
build a model of DNA
The Double-Helix Model
- Looks like a twisted ladder or
spiral staircase
- Sides of the ladder made up of
phosphate and sugar
- Each side, or strand, of DNA runs
antiparallel (opposite directions)
Base-Pairing Rule
- Bases held together by hydrogen
bonds
- A binds with T
- G binds with C
- Creates perfect fit in the center of
the helix
- Double-helix model explains
Chargaff’s rule of base pairing
(A=T; G=C)
Relationship Between DNA and Genes
- The combination of base letters
determines your traits
- Example: CATGAT = Red Hair
AGTCA = Blue Eyes
- DNA bases are like letters in a
word
- Multiple words make endless
combinations of sentences