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