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AP Biology Nucleic Acids Function: store & transmit hereditary information Examples: RNA (ribonucleic acid) DNA (deoxyribonucleic acid) Structure: AP Biology monomers = nucleotides Nucleotides 3 parts nitrogen base (C-N ring) pentose sugar (5C) ribose in RNA deoxyribose in DNA AP Biology PO4 group 2005-2006 Types of nucleotides 2 types of nucleotides different Nitrogen bases purines double ring N base adenine (A) guanine (G) pyrimidines single ring N base cytosine (C) thymine (T) AP Biology uracil (U) 2005-2006 Building the polymer AP Biology 2005-2006 Nucleic polymer Backbone sugar to PO4 bond phosphodiester bond new base added to sugar of previous base polymer grows in one direction N bases hang off the sugar-phosphate backbone Why is this important? AP Biology 2005-2006 RNA & DNA RNA single nucleotide chain DNA double nucleotide chain N bases bond in pairs across chains spiraled in a double helix double helix 1st proposed as structure of DNA in 1953 by James Watson & Francis Crick (just celebrated 60th anniversary) AP Biology Pairing of nucleotides Nucleotides bond between DNA strands H bonds purine :: pyrimidine A :: T 2 H bonds G :: C 3 H bonds Why is this important? AP Biology 2005-2006 Information polymer Function series of bases encodes information like the letters of a book stored information is passed from parent to offspring need to copy accurately stored information = genes genetic information AP Biology 2005-2006 AP Biology 2005-2006 DNA molecule Double helix H bonds between bases join the 2 strands A :: T C :: G Why is it important that the strands are bonded by H bonds? AP Biology Copying DNA Replication 2 strands of DNA helix are complementary have one, can build other have one, can rebuild the whole why is this a good system? when in the life of a cell does replication occur? mitosis AP Biology meiosis DNA replication “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” James Watson Francis Crick 1953 AP Biology 2005-2006 1953 | 1962 Watson and Crick … and others… AP Biology 2005-2006 Maurice Wilkins… and… AP Biology 1953 | 1962 2005-2006 Rosalind Franklin (1920-1958) AP Biology Interesting note… Ratio of A-T::G-C affects stability of DNA molecule 2 H bonds vs. 3 H bonds biotech procedures more G-C = need higher T° to separate strands high T° organisms many G-C parasites many A-T (don’t know why) AP Biology Macromolecule Review AP Biology Carbohydrates Structure / monomer monosaccharide Function energy raw materials energy storage structural compounds glycosidic bond Examples AP Biology glucose, starch, cellulose, glycogen Lipids Structure / building block glycerol, fatty acid, cholesterol, H-C chains Function energy storage membranes hormones Examples AP Biology ester bond (in a fat) fat, phospholipids, steroids 21 Proteins Structure / monomer amino acids levels of structure Function enzymes transport signals defense ◆ structure ◆ receptors ◆ peptide bond Examples AP Biology digestive enzymes, membrane channels, insulin hormone, actin Know the Differences Between Levels of Protein Structure! Denaturation of Proteins 24 Changing Tertiary Structure… 25 Denaturation and the Active Site 26 Nucleic acids Structure / monomer nucleotide Function information storage & transfer Examples AP Biology DNA, RNA phosphodiester bond Why does ethanol precipitate DNA? DNA is negatively charged because of phosphate backbone Ion-dipole interactions between water and phosphate stabilize DNA structure Lots of ethanol removes water of hydration around phosphates Na+ ions (from salt) step in and force changes in DNA structure, leading to precipitation Wiki article on ethanol precipitation very helpful 28 29 Denatured (precipitated) DNA 30 Grid In Question on Nucleic Acids A scientist extracts DNA from the nucleus of cells and sequences it. The scientist determines that 27% of the nucleotide bases are guanine. What percentage of the bases are thymine? In DNA, G=C and A=T If 27% are G, then 27% are C: 54% G=C Therefore 46% of bases are A=T; 23% thymine and 23% adenine 31 Practice Grid-in 2 A sample of DNA contains 21% adenine. What percentage of the DNA is cytosine? 32