Nucleic Acids

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Information about Nucleic Acids

Published on February 24, 2014

Author: drmustansar


PowerPoint Presentation: Nucleic Acids PowerPoint Presentation: Information encoded in a DNA molecule is transcribed via synthesis of an RNA molecule The sequence of the RNA molecule is "read" and is translated into the sequence of amino acids in a protein. Nucleic Acids Are Essential For Information Transfer in Cells Central Dogma of Biology: Central Dogma of Biology Replication DNA replication yields two DNA molecules identical to the original one, ensuring transmission of genetic information to daughter cells with exceptional fidelity. Transcription The sequence of bases in DNA is recorded as a sequence of complementary bases in a single-stranded mRNA molecule. Central Dogma of Biology: Central Dogma of Biology Translation Three-base codons on the mRNA corresponding to specific amino acids direct the sequence of building a protein. These codons are recognized by tRNAs (transfer RNAs) carrying the appropriate amino acids. Ribosomes are the “machinery” for protein synthesis. Nucleic Acids: Nucleic Acids First discovered in 1869 by Miescher. Found as a precipitate that formed when extracts from nuclei were treated with acid. Compound contained C, N, O, and high amount of P. Was an acid compound found in nuclei therefore named nucleic acid Nucleic Acids: Nucleic Acids 1944 Oswald, Avery, MacLeod and McCarty demonstrated that DNA is the molecule that carrier genetic information. 1953 Watson and Crick proposed the double helix model for the structure of DNA Nucleic Acids: Nucleic Acids Nucleic acids are long polymers of nucleotides. Nucleotides contain a 5 carbon sugar, a weakly basic nitrogenous compound (base), one or more phosphate groups. Nucleosides are similar to nucleotides but have no phosphate groups. PowerPoint Presentation: Pentoses of Nucleotides D-ribose (in RNA) 2-deoxy-D-ribose (in DNA) The difference - 2'-OH vs 2'-H This difference affects secondary structure and stability Nitrogenous Bases: Nitrogenous Bases Bases are attached by b-N-glycosidic linkages to 1 carbon of pentose sugar – (Nucleoside): Bases are attached by b-N-glycosidic linkages to 1 carbon of pentose sugar – (Nucleoside) Nucleosides: Nucleosides Base is linked via a b-N-glycosidic bond The carbon of the glycosidic bond is anomeric Named by adding -idine to the root name of a pyrimidine or -osine to the root name of a purine Conformation can be syn or anti Sugars make nucleosides more water-soluble than free bases PowerPoint Presentation: Anti- conformation predominates in nucleic acid polymers Nucleotides: Nucleotides Phosphate ester of nucleosides The plane of the base is oriented perpendicular to the plane of the pentose group: The plane of the base is oriented perpendicular to the plane of the pentose group PowerPoint Presentation: Other Functions of Nucleotides Nucleoside 5'-triphosphates are carriers of energy Bases serve as recognition units Cyclic nucleotides are signal molecules and regulators of cellular metabolism and reproduction PowerPoint Presentation: ATP is central to energy metabolism GTP drives protein synthesis CTP drives lipid synthesis UTP drives carbohydrate metabolism PowerPoint Presentation: Nucleotide monomers are joined by 3’-5’ phosphodiester linkages to form nucleic acid (polynucleotide) polymers Nucleic Acids: Nucleic Acids Nucleic acid backbone takes on extended conformation. Nucleotide residues are all oriented in the same direction (5’ to 3’) giving the polymer directionality. The sequence of DNA molecules is always read in the 5’ to 3’ direction Bases from two adjacent DNA strands can hydrogen bond: Bases from two adjacent DNA strands can hydrogen bond Guanine pairs with cytosine Adenine pairs with thymine Base pairing evident in DNA compositions: Base pairing evident in DNA compositions Base compositions experimentally determined for a variety of organisms PowerPoint Presentation: H-bonding of adjacent antiparallel DNA strands form double helix structure Properties of DNA Double Helix: Properties of DNA Double Helix Distance between the 2 sugar-phosphate backbones is always the same, give DNA molecule a regular shape. Plane of bases are oriented perpendicular to backbone Hydrophillic sugar phosphate backbone winds around outside of helix PowerPoint Presentation: Noncovalent interactions between upper and lower surfaces of base-pairs (stacking) forms a closely packed hydrophobic interior. Hydrophobic environment makes H-bonding between bases stronger (no competition with water) Cause the sugar-phosphate backbone to twist. View down the Double Helix: View down the Double Helix Sugar-phosphate backbone Hydrophobic Interior with base pair stacking Structure of DNA Double Helix: Structure of DNA Double Helix Right handed helix Rise = 0.33 nm/nucleotide Pitch = 3.4 nm / turn 10.4 nucleotides per turn Two groves – major and minor PowerPoint Presentation: Within groves, functional groups on the edge of base pairs exposed to exterior involved in interaction with proteins. Factors stabilizing DNA double Helix: Factors stabilizing DNA double Helix Hydrophobic interactions – burying hydrophobic purine and pyrimidine rings in interior Stacking interactions – van der Waals interactions between stacked bases. Hydrogen Bonding – H-bonding between bases PowerPoint Presentation: Charge-Charge Interactions – Electrostatic repulsions of negatively charged phosphate groups are minimized by interaction with cations (e.g. Mg 2+ )

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