Chap. 10 : Nucleic Acids & Protein Synthesis I. DNA – deoxyribonucleic acid - function – store and use information to direct activities of the cell and to make exact copies of itself. - function – store and use information to direct activities of the cell and to make exact copies of itself.

- made up of repeating subunits called nucleotides - made up of repeating subunits called nucleotides A. Nucleotide A. Nucleotide - made up of 3 parts : - made up of 3 parts : 1. 5 – carbon sugar called deoxyribose 1. 5 – carbon sugar called deoxyribose 2. phosphate group (PO) 2. phosphate group (PO) 3. nitrogen base – what causes DNA to 3. nitrogen base – what causes DNA to vary in all living things. vary in all living things.

-- 4 different bases : -- 4 different bases : 1. adenine (A) 1. adenine (A) 2. guanine (G) 2. guanine (G) 3. thymine (T) 3. thymine (T) 4 cytosine (C) 4 cytosine (C) B. Double Helix - nucleotides bond together to form strands. 2 strands bond together in the shape of a spiral twist called a double helix. Discovered by Watson and Crick (1953) - nucleotides bond together to form strands. 2 strands bond together in the shape of a spiral twist called a double helix. Discovered by Watson and Crick (1953) Called purines (double rings) Called pyrimidines (single rings )

** Structure of DNA ** Structure of DNA H H H Sides made up of a sugar and phosphate. Held together by a covalent bond. Sides joined together by weak hydrogen bonds Purine base Pyrimidine base

Called complementary strands because : Adenine always bonds with Thymine (AT) Adenine always bonds with Thymine (AT) Cytosine always bonds with Guanine (CG) Cytosine always bonds with Guanine (CG) A-T-G-G-C-C-A-A-C-G-T-A A-T-G-G-C-C-A-A-C-G-T-A T-A-C-C-G-G-T-T-G-C-A-T T-A-C-C-G-G-T-T-G-C-A-T