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