DNA (Deoxyribonucleic Acid)

DNA is made up of repeating molecules called NUCLEOTIDES. Phosphate Group N Nitrogenous base (A, G, C, or T) CH2 O C1 C4 C3 C2 5 Sugar (deoxyribose)

Watson & Crick proposed… DNA had specific pairing between the nitrogen bases: ADENINE – THYMINE CYTOSINE – GUANINE DNA is made of 2 long strands of nucleotides arranged in a specific way called the “Complementary Base-Pair Rule”

DNA Double Helix “Rungs of ladder” Nitrogenous Base (A,T,G or C) “Legs of ladder” Phosphate & Sugar Backbone

Nitrogenous Bases PURINES 1. Adenine (A) 2. Guanine (G) PYRIMIDINES 3. Thymine (T) 4. Cytosine (C) A or G T or C

Chargaff’s Rule Adenine must pair with Thymine Guanine must pair with Cytosine Their amounts in a given DNA molecule will be about the same. H-bonds T A G C

(1961) Watson & Crick proposed… …DNA controlled cell function by serving as a template for PROTEIN structure 3 Nucleotides = a triplet or CODON (which code for a specific AMINO ACID) AMINO ACIDS are the building blocks of PROTEINS

DNA Double Helix P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A